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Title (dcterms:title)
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Eng
Reproductive Success and Population Stability of Seven Raptor Species Following the Great Colorado Flood of 2013
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Date (dcterms:date)
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2016
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Creator (dcterms:creator)
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Eng
Hruska, Rhianna M
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Subject (dcterms:subject)
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Eng
Environmental Studies
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extracted text (extracttext:extracted_text)
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REPRODUCTIVE SUCCESS AND POPULATION STABILITY
OF SEVEN RAPTOR SPECIES FOLLOWING
THE GREAT COLORADO FLOOD OF 2013
by
Rhianna M. Hruska
A Thesis
Submitted in Partial Fulfillment
of the Requirements for the Degree
Master of Environmental Studies
The Evergreen State College
June 2016
©2016 by Rhianna Hruska. All rights reserved.
This Thesis for the Master of Environmental Studies Degree
by Rhianna M. Hruska
has been approved for
The Evergreen State College
by
________________
Kevin Francis, Ph.D.
Director, Graduate Program on the Environment
Member of the Faculty
______________
Date
ABSTRACT
Reproductive Success and Population Stability of Seven Raptor Species Following the
Great Colorado Flood of 2013
Rhianna M. Hruska
Keywords: Raptor Monitoring, Raptor Reproductive Success, Bald Eagle, Osprey, Great
Horned Owl, Red-Tailed Hawk
Raptor monitoring data has been recorded on seven raptor species in Longmont,
Colorado from 2012 to 2015. These species are Bald Eagle (Haliaeetus leucocephalus),
Red-Tailed Hawk (Buteo jamaicensis), Osprey (Pandion haliaetus), Great Horned Owl
(Bubo virginianus), Cooper’s Hawk (Accipiter cooperii), Swainson’s Hawk (Buteo
swainsoni), and the Barn Owl (Tyto alba). The observations were collected by staff and
volunteers for the City of Longmont’s Open Space division. In early September 2013, a
flash flood damaged infrastructure and natural habitat in Longmont, Colorado. This
thesis looks at the changes in the reproductive success of these raptor species after the
Great Colorado Flood of September 2013. The impact of natural disasters on raptor
populations has been rarely studied, and this research will enhance the understanding of
how raptor populations change in response to a major flood event. With climate change
implications on the rise, this study could be vital for informing raptor population
management strategies for cities.
Table of Contents
Table of Contents……………………………………………………………………......vi
List of Figures………………………………………………………...……………….... ix
List of Tables……………………………………………………………………………..x
Acknowledgements………………………..…………..……………………………..….xi
Preface……...……………………………………………………………………………..1
Chapter 1: Introduction: The City of Longmont and its Raptors….….……………..2
Chapter 2: Raptor Monitoring Data Literature Review…………………..…………..8
Raptor Monitoring Data…………………………………………………………...9
Raptor Monitoring Techniques and Considerations………………………………9
Raptor Monitoring and Citizen Science Data Collection………………………..11
The Great Colorado Flood of 2013………………………………………………12
Birds and Climate Change……………………………………………………….13
Raptors and Natural Disaster…………………………………………………….14
Literature Review Conclusion……………………………………………...........15
Chapter 3: Methods: Longmont Raptor Monitoring Volunteer Program………….17
Site Description…………………………………………………………………..21
Development History of Longmont…………………………………………...…22
Great Colorado Flood of 2013 Infrastructure Damages to Longmont…………...23
Determining Which Species to Include in this Study……………………………25
Differences Between Monitoring Years…………………………………………25
Geographic Information Systems (GIS)………………………………................26
Chapter 4: Raptor Species Nesting Behaviors……………………..…………………28
Bald Eagle (Haliaeetus leucocephalus)…………………….………......………..28
Osprey (Pandion haliaetus)…………………………………………………...…29
Red-Tailed Hawk (Buteo jamaicensis)…………………………………….….…30
Great Horned Owl (Bubo virginianus)…………………………………………..31
Barn Owl (Tyto alba)…………………………………………………………….31
vi
Cooper’s Hawk (Accipiter cooperii)……………………………………………..32
Swainson’s Hawk (Buteo swainsoni)…………………………………..………...33
Chapter 5: Results and Discussion……………………………………………….……34
1. Research Question…………………………………………………………...34
2. Reproductive Success………………………………………………………..35
3. Raptor Populations and the Flood of September 2013………………………35
Results………………………………………………………………..35
Discussion…………...………………………………………………………36
4. Chicks Successfully Fledged by Year………………………………………..37
Chicks Successfully Fledged in 2012………………………………...37
Chicks Successfully Fledged in 2013……………………………..….38
Chicks Successfully Fledged in 2014………………………………...39
Chicks Successfully Fledged in 2015…………………………...……40
5. Nests Observed for all Four Years………………………………………...…41
6. Nest Failures from 2012 to 2015…………………………………………….42
Nest Failure by Species……………………………………………....42
Nest Failure by Year…………………………………………………43
7. Nest Occupation Changes from 2012 to 2015…………………………….…44
Changes in Species in Each Nest………………………….…………44
Nests that were Consistently Occupied by the Same Species…....…..44
Changes in Nest Occupation……………………………………...….44
8. Nest Densities for BAEA, GHOW, OSPR, and RTHA………………...……45
Nest Density for Bald Eagles……………………………………..….45
Nest Density for Great Horned Owls………………………………...46
Nest Density for Ospreys……………………………………….……47
Nest Density for Red-Tailed Hawks………………………………….48
9. Observation Time Per Nest from 2012 to 2015……………………...………50
10. Conclusion………………………………………………………………...…55
11. Appendix: Reproductive Success by Raptor Species………………………..56
Chapter 6: Recommendations and Further Research……………………………..…57
Recommendations: Photo Point Monitoring and Habitat Quality……………….57
Photo Points and Raptor Nests…………………………………………….……..59
Raptor Nest Cameras…………………………………………………………….59
Further Research: Nest Density and Spatial Location…………………..……….60
Chapter 7: Conclusion………………………………………………………………….63
vii
Appendix…………………………………………………………………………..…….66
Reproductive Success by Species………………………………………………..66
Bald Eagle………………………………………………………………..66
Red-Tailed Hawk…………………………………………………….…..66
Osprey……………………………………………………………………67
Great Horned Owl…………………………………………………...…..68
Cooper’s Hawk…………………………………………………….…….68
Swainson’s Hawk…………………………………………………...……68
Barn Owl………………………………………………………...……….69
References………...……………………………………………………………………..70
viii
List of Figures
Figure 3.1. Completed City of Longmont Raptor Monitoring Volunteer Form……..….21
Figure 3.2. City of Longmont Bike Map……….…………….………………...……….24
Figure 3.3. Greenways in the City of Longmont……………………………….….……24
Figure 3.4. Nest Minutes/Hours Observed Per Year from 2012 to 2015………………..26
Figure 5.1. Number of Fledglings Per Year Per Species from 2012 to 2015……...……37
Figure 5.2. Fledgling Success in Nests Monitored for Four Years…………….….…….42
Figure 5.3. Observation Minutes and Hours by Longmont Staff and Volunteers………50
ix
List of Tables
Table 1.1. American Ornithological Union 4 Letter Code for 7 Raptor Species……....…4
Table 5.1. Chicks Successfully Fledged in 2012……………………………………..…37
Table 5.2. Chicks Successfully Fledged in 2013…………………………….….………38
Table 5.3. Chicks Successfully Fledged in 2014………………………….…………….49
Table 5.4. Chicks Successfully Fledged in 2015………………...……………………...40
Table 5.5. Bald Eagle Nest Density, Nearest Two Nests………...………………..…….45
Table 5.6. Great Horned Owl Nest Density, Nearest Two Nests…………………..……46
Table 5.7. Osprey Nest Density, Nearest Two Nests…………………...……………….47
Table 5.8. Red-Tailed Hawk Nest Density, Nearest Two Nests………………...………48
Table 5.9. Minutes Observed Per Nest from 2012 to 2015………………………….…..53
x
Acknowledgements
I am incredibly grateful for the opportunity to complete a graduate thesis. My
writing and research skills have grown immensely from this experience. My MES thesis
stemmed from the support of my family, professors, colleagues, and friends. To my
parents, Gary and Arunee Hruska, and my twin brothers, Randy and Ryan Hruska, who
are continuously supportive of my pursuits in higher education.
Many thanks to my thesis reader, Professor Kevin Francis, for supporting me
since my first day in MES, and for providing invaluable advice throughout the entire
thesis process. A thesis is an overwhelming task, and he helped me break it down step by
step until completion. I am grateful to Professor Erin Martin, for the thorough comments
on my writing, which helped me articulate my ideas throughout my time in MES. The
many times we discussed my thesis greatly influenced and determined my final thesis
research questions.
This thesis topic would not have been possible without the generosity of the City
of Longmont, Colorado and its Open Space division staff. I am happy to have interned
for Lauren Poulos, who taught me everything I know about photo point monitoring and
volunteer coordination, and who kindly sponsored my MES internship during the summer
of 2015. I am glad to have worked with Longmont’s Natural Resources Specialist Jim
Krick, who provided me with the necessary data, materials, and observations to run my
analyses for this thesis. I am also grateful to fellow University of California, Santa Cruz
alum and Longmont City Planner Ian Colby, for the guidance on Longmont’s
cartography and development. Lastly, I appreciate all the City of Longmont volunteers
who dedicated their time to the raptor monitoring volunteer program from 2012 to 2015.
The participation of all these volunteers ensures the detailed tracking of reproductive
success in raptor nests throughout the city, and their time and meticulous observations
have provided most of the on-the-ground data for this thesis.
To Evergreen Writing Center staff member Dr. Michael Radelich, thank you for
benevolently working one-on-one with me to improve the style and detail in my writing.
I brought draft after draft to Dr. Radelich’s office and his writing expertise has defined
this thesis to become more clear and eloquent than it would have been otherwise.
To my MES Fall 2014 cohort, all of your perspectives are appreciated and have
shaped my graduate experience at Evergreen. To my peer review group, Hannah
Trageser, Heather May, and Ryan Hobbs, thank you for all your advice on my drafts
throughout the thesis process.
To my co-workers and dear friends, Stephen D’Annibale, Anna Rhoads, and
Jonas Upman, for all your encouragement during the ups and downs of my graduate
studies. Stephen D’Annibale, I could not have completed my GIS maps without your
quick-witted problem-solving abilities and patient guidance. Anna Rhoads, you are
always there for me whenever I need someone to talk to, and you never hesitate to lend
your time, home, tea, and adorable, furry cats to my assistance whenever I need it. Our
many MES writing sessions at various Olympia coffee shops have led to the development
of this thesis. Jonas Upman, your drive continues to inspire me and your trust in my
abilities is much appreciated throughout the many academic goals I set for myself.
xi
Preface
I chose to focus my Master of Environmental Studies thesis on the City of
Longmont, Colorado after interning with the city’s Natural Resources Department
Volunteer Coordinator. Over the course of my internship during the summer of 2015, I
learned the protocols for the raptor and photo point monitoring volunteer programs. This
thesis and the research involved is a result of my experience working with the staff and
volunteers that summer and the information from the City of Longmont’s raptor
monitoring data set.
This thesis looks at the reproductive success of seven raptor species in Longmont,
Colorado. Chapter 1 introduces the Great Colorado Flood of 2013 and its effects on
Boulder County, the seven raptor species, and the main thesis research question. Chapter
2 covers the literature available on the Great Colorado Flood of 2013, raptor reproductive
success studies, raptor monitoring techniques, and citizen science contributions. This
chapter also highlights a gap in the literature for studies on the impact of natural disasters
on raptors. Chapter 3 reviews the raptor monitoring volunteer program observation
protocols. Chapter 4 details the nesting behaviors and relevant life history characteristics
that are important to keep in mind when looking at the reproductive success of a raptor
species. Chapter 5 analyzes the reproductive success of each species over the four years
of monitoring. This chapter also goes over the nests that failed over the course of the
raptor monitoring program. Chapter 6 explores the idea of combining two already
existing City of Longmont volunteer programs, raptor monitoring and photo point
monitoring, to provide more information to the raptor monitoring volunteer program.
This chapter also covers recommendations for future areas of research. The raptor
monitoring dataset could also be used to determine the nest density and spatial location of
nests in Longmont. Chapter 7 reinforces the importance of raptor monitoring in cities,
citizen science efforts, and the increasing implications of climate change on wildlife.
This thesis is a reference point for other studies on the impact of natural disasters,
especially flooding, on raptor species.
1
Chapter 1: Introduction: The City of Longmont and its Raptors
City of Longmont Open Space Vision:
Connecting people with our natural resources;
Respecting our environment;
Defining our community
Balancing our growth;
Treasuring our children’s future;
Protecting what we value.
On September 9, 2013, heavy rains started pouring down on the Front Range of
Colorado. The rain continued for a week, forming a 500-year flood which worked its
way through seventeen Colorado counties, with Boulder County being one of them. A
500-year flood means that there was a 0.2% chance that a flood of that magnitude would
occur in a year. The flood resulted in over a billion dollars of infrastructure damage and
eight lives lost and six missing (A. Smith, National Climatic Data Center, 2014, personal
communication; NWS 2014) (Gochis et al. 2015). Residents of Boulder County had not
experienced a flash flood of this magnitude in decades, and had no recent memory of how
to cope with the damage that had suddenly been inflicted on their communities (Albright
& Crow, 2015). Monetary aid was provided by the Federal Emergency Management
Agency (FEMA) and the rebuilding of lost infrastructure began shortly after the flood
waters receded. Cities impacted by the flood held public meetings on a variety of
recovery topics, like stream restoration or land use, to engage residents regarding the
direction of future recovery efforts (Albright & Crow, 2015).
Communities have moved forward since the natural disaster, and these
improvements can be visibly seen through several infrastructure projects like bridges
being rebuilt and recreational trails being re-established.
2
What has not been addressed is the impact of the flood on Boulder County’s
wildlife. The effects of natural disasters on avian species have not been extensively
studied. Birds are a colorful part of an ecosystem and are often admired and appreciated
by their observers. The stability of their populations must be monitored to ensure that
these avian species are not struggling to survive in Boulder County.
The flood left a lasting impression on the residents of Northeastern Colorado and
they have many stories to tell of their experiences during and after the flood. This thesis
focuses on the City of Longmont, Colorado and the impacts of the flood of 2013 on seven
raptor populations being monitored by Longmont’s Public Works and Natural Resources
department Open Space division staff. The seven raptor species are: Bald Eagle
(Haliaeetus leucocephalus) (BAEA), Red-Tailed Hawk (Buteo jamaicensis) (RTHA),
Osprey (Pandion haliaetus) (OSPR), Great Horned Owl (Bubo virginianus) (GHOW),
Barn Owl (Tyto alba) (BNOW), Swainson’s Hawk (Buteo swainsoni) (SWHA), and
Cooper’s Hawk (Accipiter cooperii) (COHA). The acronyms for each species are the
four-letter codes designated by the American Ornithologists’ Union. These birds of prey
are influential species in Boulder County. These raptor species all have an International
Union for Conservation of Nature status of Least Concernhos, which means that the
species population has been evaluated and does not fit into the other categories (like
Threatened or Critically Endangered).
3
Species (Common Name)
Species (Scientific Name)
AOU Four Letter Code
Bald Eagle
Haliaeetus leucocephalus
BAEA
Red-Tailed Hawk
Buteo jamaicensis
RTHA
Osprey
Pandion haliaetus
OSPR
Great Horned Owl
Bubo virginianus
GHOW
Cooper’s Hawk
Accipiter cooperii
COHA
Swainson’s Hawk
Buteo swainsoni
SWHA
Barn Owl
Tyto alba
BNOW
Table 1.1. American Ornithological Union (AOU) 4 Letter Code
for the Seven Raptor Species
Since the Great Colorado Flood of September 2013, human behaviors have
changed to reflect the drastically altered environment they reside in. For example, the
Sunset Bridge, a bridge right next to the City of Longmont Sunset Campus, was heavily
damaged by the 500-year flood and the bridge was not reopened for use by pedestrians,
cyclists, and vehicles until May 2016. Since the bridge was blocked off and no longer
accessible, residents began commuting using alternate routes when navigating the area,
which eventually turned into habit as residents learned where they could and could not
drive their vehicles through Longmont. This change in behavior can also be noticed in
the cycling community. Sandstone Ranch, a historic house and public open space in the
City of Longmont, has seen less bike traffic through the greenway since the pedestrian
bridge that connects the ranch and the greenway was destroyed by the flood. The
Sandstone Ranch staff reminisce on the days before the flood when residents would often
bike from the suburbs of town to have picnics at Sandstone Ranch. Since the bridge was
4
taken out, fewer residents frequent the public open space, and if they do, they will drive
to the ranch instead.
There are significant differences in how people have adapted to the scattered
infrastructural damage that is evident throughout Longmont. Taking this change into
account, wildlife populations may have had a similar measurable impact since habitat has
been noticeably altered by the flood. Trees were felled, the Saint Vrain Creek (the main
creek that runs across Longmont) changed course, and habitat quality was compromised
by the natural disaster.
For the past few years, flooding has been a major issue in the Front Range of
Colorado, which is the urban corridor along the east side of the Rocky Mountain range,
and the raptor monitoring observation program can determine how the frequent flooding
is impacting the raptor species in Longmont. The increasing flood occurrences are a
reflection of changing climate and research needs to be done on how the raptors are
responding to these climate events. Climate change could be directly impacting the prey
availability, range, and habitat quality of raptors in Colorado. This work would advance
scholarship because unanticipated large-scale flood events may happen elsewhere and
this study could be a much needed reference point for analyzing how raptors respond to
natural disaster.
The raptor monitoring data was collected to give the Open Space staff members
an idea of what may be occurring with the raptor populations and they are interested in
seeing the patterns that arise from the past four years of observations. Recommendations
can be made for what data was particularly useful for different kinds of analyses for this
thesis. This could influence data collection for future years of raptor monitoring in
5
Longmont. This research is also important because it includes citizen science.
Volunteers that watch over a nest for a few months develop more of a connection to the
raptors and often share their insights with passerby who may ask what they are observing
through their binoculars.
The City of Longmont Natural Resources Department will be able to utilize this
thesis to inform the structure of their raptor monitoring program and policies. This thesis
could also shape the volunteer program to focus on nests of concern or to train the
volunteers to look out for other avian behaviors or environmental factors while they are
making their observations. From this thesis, City of Longmont staff will have more
information on the trends that may be occurring in the different raptor populations and
can focus their efforts on each species.
The main research question for this thesis is: How have raptor populations in
Longmont been impacted by the Great Colorado Flood of September 2013? One subquestion is: What was the reproductive success of each of the raptor species monitored in
Longmont, Colorado from 2012-2015? Another sub-question is: What is the approximate
nest density of the Bald Eagle, Great Horned Owl, Osprey, and Red-Tailed Hawk nests in
Longmont, Colorado? These questions will be answered using Geographic Information
Systems software, JMP Pro 12 statistics and graph building software, and raptor
monitoring observations by City of Longmont, Colorado staff and volunteers.
Chapters 3 and 4 will discuss the background information of the seven raptor
species being monitored and a description of the City of Longmont as a study area. A
literature review will cover the use of citizen science in avian research, previous natural
disaster and raptors studies, prey and habitat requirements of raptors, and information on
6
the 2013 Colorado Front Range Flood. The methods section will detail the protocols
established by the City of Longmont raptor monitoring volunteer program to collect the
reproductive success data. The discussion will cover raptor nesting behaviors that relate
to the research question in this study. The results will go over which species occupied
different nests and how many nests failed each year. The conclusion will include
recommendations for future areas of study and raptor monitoring programs in cities.
7
Chapter 2: Raptor Monitoring Data Literature Review
The City of Longmont, Colorado, is in the Northeastern portion of Boulder
County. The main creeks in Longmont are Left Hand Creek, Boulder Creek, and St.
Vrain Creek. A study conducted by Albright and Crow (2015) looked at the community
outreach efforts conducted by seven Colorado cities, including Longmont, heavily
affected by the flood of 2013. The research was looking at steps taken after the flood and
policy changes to increase resilience in case a devastating flash flood were to occur
again.
Avian monitoring data has been used to answer a wide array of research questions
in a variety of fields. Monitoring data allows researchers to track changes in bird
populations over time. This literature review will explore the versatility of monitoring
data and the power of citizen science observations in bird counts. It will review the
literature available on the Colorado Flood of September 2013, with a focus on its impacts
on the City of Longmont. The influence of natural disasters on raptors will be reviewed.
The effects of climate change on birds will be discussed, especially in relation to flood
events. Monitoring techniques relevant to the species in this thesis will be brought up
and kept in mind throughout data analysis. The City of Longmont raptor monitoring data
can be utilized to determine the reproductive success and nest density of seven species
before and after the flood. The conclusion of this chapter will describe the gap in the
literature that this thesis intends to address.
8
Raptor Monitoring Data
Looking at Raptor Monitoring data overall, the information gathered has been
analyzed in various ways. The literature is extensive and raptor monitoring data
continues to answer significant research questions. One of the benefits to collecting years
of raptor monitoring data is that the raptor populations can be analyzed by year or over
time. In the case of my research, the four years of data from Longmont, Colorado could
help inform the city’s environmental management policies. I have raptor monitoring
observations from two years before the flood and two years after the flood. My research
question focuses on the impact of the flood on the reproductive success of raptors in
Longmont.
Most of the literature available uses raptor monitoring data to look at nest density,
nest occupation, reproductive success, behavior, or proximity to urban areas. Raptors
have also been studied for species interactions or dietary preferences. The literature has
encompassed a variety of different raptor species depending on where in the world the
research was carried out. What is lacking in the literature is research on the impact of
natural disasters on raptors. Much of this is due to the fact that natural disasters are
incredibly unpredictable and raptor monitoring data may not have been collected in an
area before a natural disaster occurs. It is also possible that raptor monitoring
observations may be recorded for years and a natural disaster may not have happened
within the years the data has been collected.
Raptor Monitoring Techniques and Considerations
City of Longmont Open Space staff members divide their time between multiple
natural resources projects that need to be completed throughout the year. In order to meet
9
these deadlines, staff spend at least five minutes observing a raptor nest before either
moving on to observe another nest or shifting to a separate task, like the removal of
invasive plants. The staff recognize the need to rely on citizen science to accumulate
longer and more frequent observations of a nest.
For the field of raptor monitoring, a minimum of two raptor nest observations
needs to be made in order to determine nest productivity (Bird and Bildstein 2007). The
first observation would be when the raptors start nesting and the second right before the
chicks fledge (Bird and Bildstein 2007). It can be challenging to determine an ideal time
to conduct the two observations since raptor species often nest at different times (Bird
and Bildstein 2007). An example of this can be seen in the nesting preferences of two
species in this Longmont, Colorado study: Great Horned Owl (Bubo virginianus)
(GHOW) and Red-Tailed Hawk (Buteo jamaicensis) (RTHA). Great Horned Owls do
not build their own nests and often use the nests of other species, particularly Red-Tailed
Hawks (Olendorff 1973, Stokes and Stokes 1989, Hammond and Pearson 1993). The
nesting behavior of the Great Horned Owls usually does not interfere with that of RedTailed Hawks since Great Horned Owls nest earlier than Red-Tailed Hawks do
(Olendorff 1973, Stokes and Stokes 1989). The two observations of raptor nests, at the
beginning and end of the nesting season, could potentially miss a species or nest if done
too early or too late in the nesting cycle.
Aerial surveys to determine reproductive success are often best if two overall
observations are going to be made since the level of accuracy when counting chicks can
be better depending on the species being monitored (Bird and Bildstein 2007). The
success of this aerial technique varies depending on the size of the nests and the tendency
10
for a species to nest at open sites, which applies to species such as Ospreys (Pandion
haliaetus) (OSPR) and Bald Eagles (Haliaeetus leucocephalus) (BAEA) (Poole 1989,
Hammond and Pearson 1993, Bird and Bildstein 2007). Since not all species nest at open
sites, especially Great Horned Owls, which are known to nest on cliffs, aerial surveys are
not always the best way to assess the populations of some raptors (Stokes and Stokes
1989, Bird and Bildstein 2007). In Longmont, Great Horned Owls will nest in the cliff
sides of city owned Sandstone Ranch. Since City of Longmont staff are monitoring
multiple raptor species each year, citizen science is preferable for tracking the
productivity of adult raptor pairs each nesting season.
Raptor Monitoring and Citizen Science Data Collection
My raptor monitoring observation data was collected by City of Longmont staff
and volunteers. Since the City of Longmont Open Space division only has a few staff
members, the majority of my data set was collected with the help of citizen science
efforts. Not as many raptor monitoring articles are written with volunteer observations
compared to staff or scientist observations, but the publishing of citizen science research
has previously been done in Boulder County, Colorado (Blumstein 1989, Jones 1989,
Gietzen 1996). The Boulder County Nature Association is a non-profit that has been
surveying raptors since 1983 (Jones 1989). Their observations are collected by
volunteers and have been published in collaboration with university researchers in
Colorado and neighboring states (Blumstein 1989, Jones 1989).
The Christmas Bird Count (CBC) is a dataset that attributes its success solely to
citizen science efforts. The CBC occurs between December 14 to January 5 every year
and local counts happen on one day that falls between those dates. The CBC makes it
11
possible for scientists to look at changes in bird populations, particularly distribution and
abundance, over time (Dunn, E., Francis, C., & Blancher, P. et al. 2005). “The [CBC],
conducted by the National Audubon Society (NAS) since 1900, constitutes the longestrunning and geographically most widespread survey of bird life in the Western
Hemisphere (Dunn, E. et al. 2005). This citizen science reliant data set, with “more than
50, 000 observers [participating] each year,” has provided a valuable opportunity to better
understand bird species in the winter (Dunn, E. et al. 2005). Although the CBC is an
incredible resource to scientists, due to its duration, one of the challenges of the CBC
data is the change in protocol over time (Dunn, E. et al. 2005). Though Longmont’s
raptor observations are much shorter than the CBC, even the four year span the volunteer
program encompasses presents its opportunities and challenges. One benefit is that there
is a myriad of observations on raptor nests throughout the city. One challenge is the
differences in the number of volunteers and observation effort each year. Since the
program started in 2012, raptor monitoring observations were collected before the
September 2013 flood, making it possible to gauge the reproductive success of multiple
raptor species in relation to the 500-year flood.
The Great Colorado Flood of September 2013
The Great Colorado Flood of September 2013 was a powerful natural disaster that
provides a unique opportunity to design a natural experiment. Much of the literature on
this flood focuses on the meteorological factors that occurred to cause a flood of this
magnitude. Other than weather effects, there is also literature on the potential policy
changes that could be made and the economic impacts of the flood on the Colorado Front
12
Range (Albright & Crow 2015). The impacts on wildlife from the flood have not been
studied.
In 2015, Gochis et al. published a comprehensive meteorological analysis of the
weather events associated with the Great Colorado Flood of September 2013 (Gochis, D.,
Schumacher, R., Friedrich, K. et al. 2015). From September 9-13, 2013, Colorado
received record rainfall, which led to a 500-year flood that caused over two billion U.S.
dollars worth of damage and resulted in eight fatalities (A. Smith, National Climatic Data
Center, 2014, personal communication; NWS 2014) (Gochis et al. 2015). “Of the 18
counties designated for assistance, Boulder County was hardest hit in terms of damages
receiving more than $33 million in state and federal reconstruction grants (FEMA) and
over 150 miles of road were destroyed in Boulder County alone (28 Sep, Daily Camera)”
(Gochis et al. 2015).
Birds and Climate Change
Since this study is on the effects of a flood on raptors, it is important to look at the
research being done on climate change and its impacts on avian populations. In a 2004
study by Humphrey Q. P. Crick, the impact of weather on bird populations is explored
using multiple case studies of species from different guilds that reside around the world
(Crick 2004). “Extreme weather events, such as prolonged frozen spells and droughts,
can have catastrophic effects on bird populations, including long-term effects on whole
cohorts (Stenseth et al. 2002)” (Crick 2004). Crick’s research provides case studies from
multiple bird families and does not just focus on raptors (Crick 2004). What is not
covered in this particular study is the impact of a natural disaster like flooding. The study
13
reviewed other articles with research from around the world in the field of birds and
climate change in order to draw its conclusions.
Lastly, the article brings up the important point of frequency of climate change
events and their potential long term impacts on birds (Crick 2004). Increased flood
events are occurring in many regions in the world and this study in Colorado can be a
reference point. Though my data set encompasses four years, this research would add to
the literature by describing what may be occurring to raptors in the Front Range of
Colorado and allow for long-term studies to be conducted if the frequency of flooding in
the region continues to increase.
Raptors and Natural Disaster
What is not often studied is the response of raptor populations to natural disaster
or other sudden environmental stressors. The most common natural disasters
incorporated into the raptor monitoring literature are high wind and storm events
(Penteriani, V., Mathiaut, M., and Boisson, G. 2002; Martinez, J., Jimenez-Franco, M.,
Zuberogoitia, I., et al. 2013). A study conducted in the Southeast of Spain focused on the
impact of strong winds and heavy snowfall on three different raptor populations
(Martinez, J. et al. 2013). Having three raptor populations allowed for a one-way
ANOVA analysis in their study (Martinez et al. 2013). Another study in France looked at
“windthrow effects on density, productivity, nesting stand choice, and fidelity in
Northern Goshawks” (Penteriani, V. et al. 2002). Both studies in Europe found that the
species under study had stable populations after the high wind natural disaster events
(Penteriani et al. 2002, Martinez et al. 2013). The high winds destroyed nests and felled
trees, but the raptors would either build new nests or fix up the damaged ones (Penteriani
14
et al. 2002, Martinez et al. 2013). The raptor populations were relatively stable after the
natural disasters (Penteriani et al. 2002, Martinez et al. 2013). Since studies on the
impacts of natural disasters on raptors are so rare, the Martinez et al. study cited research
on other animals being impacted by wind events (2013). The references of the study
included research that had been conducted on insects, bettongs, and bears (Martinez et al.
2013). The impacts of natural disasters on wildlife in general would be beneficial to
focus on since climate change events around the world affect wildlife in different ways.
There is a significant gap in the literature in regards to raptor populations and
their responses to heavy flood events. Studies have been conducted on flood control
projects and impacts on bird species (Shapiro, A., Montalbano III, F., & Mager, D. 1982).
In central Florida, Shapiro et al. focused on southern Bald Eagle nesting activity and
whether a flood control project impacted the raptors. They found “a 74% decrease in the
annual number of active territories […] following construction of this flood control
project […] where disruption of aquatic ecosystems […] was most severe” (Shapiro et al.
1982). There was a measurable negative impact on the southern Bald Eagle populations
(Shapiro et al. 1982). Even though this case was not a natural disaster, the planned
disturbance shows the effects that anthropogenic changes in the environment can have on
raptor species (Shapiro et al. 1982). Cities need to manage their urban expansion in order
to limit anthropogenic impacts on raptors.
Literature Review Conclusion
The use of volunteers for monitoring raptor populations within cities allows for
observations to be recorded that would not have been available otherwise. Monitoring
before a natural disaster occurs, like a flood event, provides data before a sudden change
15
occurs in the local environment. Raptor monitoring data can answer a wide variety of
research questions and cities can tailor their data collection to what they are most
interested in learning about their migratory or resident raptor species.
16
Chapter 3: Methods: Longmont Raptor Monitoring Volunteer Program
In 2012, the City of Longmont Natural Resources Department’s Open Space
Division staff members started a raptor monitoring volunteer program. There are
approximately five Open Space staff members whose time is divided between multiple
environmental projects around Longmont. The staff are too busy balancing all of these
projects to watch the raptor nests as often as they would prefer. This is where citizen
science comes in.
Though the use of citizen science has been greatly beneficial for the Open Space
division, training and working with the volunteers also takes time. The Natural
Resources budget does not allow for the hiring of another staff member to supervise these
volunteer coordination programs. Due to this budgetary restraint, the City of Longmont
applied for grant funding to create a Volunteer Coordinator position for 2015. This
position is especially useful after the flood, since much restoration work still needs to be
carried out around the city. The volunteer coordinator managed projects such as raptor
monitoring, restoration crew, adopt-a-rose garden, and various one-day restoration
events. The volunteer programs greatly benefitted from having a point person to contact
whenever volunteers needed to submit any forms or developed questions about a
volunteer program.
City of Longmont Open Space staff check the raptor nests every year to see if a
specific nest is active or not for that year. Most new nests are often located in two ways:
when the staff members are at a site for other work responsibilities, or if a resident calls
to let the department know that a raptor nest has been established in the area. The staff
monitor the birds with powerful binoculars or spotting scopes for about five minutes or
17
more. Detailed notes are taken during each observation. When checking if the nests are
active or not, the staff look for signs of raptor chicks in the nest, raptors flying or
perching near the nest, or a raptor incubating eggs in a nest.
The raptor monitoring volunteer program creates the chance for Longmont
residents to get more involved and feel connected to their community. The volunteers do
not need prior experience in order to join the program. This provides members of the
community with the opportunity to learn more about their local environment. Once staff
members have checked on the nests, active and inactive nests are assigned to volunteers.
The volunteers are asked to watch each nest(s) that they are assigned once a week for
thirty minutes at a time. The thirty minutes does not have to be at the same time each
week and volunteers often do not watch the nests at the same time throughout the season.
Many volunteers will watch a nest more than once a week or for longer than thirty
minutes as well. Many volunteers have completed multiple years in the raptor
monitoring program.
Both staff and volunteers fill out an official City of Longmont Raptor Monitoring
Volunteer form for each time they observe an individual nest. The sheet asks for
summary data to keep track of the reproductive success of the raptors. There is also a
section at the top to track date/time and weather conditions; that way if a chick is lost,
there are weather records to determine if harsh conditions may have been a factor. Notes
are taken by the observer to try and determine whether the chicks will be fledging soon,
or if the raptor male and female are properly caring for their chicks, or if the adult raptor
pair are displaying regular parenting behavior. The raptor monitoring process has also
been vital in determining any anthropogenic disturbances that may flush the raptors from
18
their nests. For example, raptors could be flushed from a nest by people who approach
the nest to try and get a closer look or take pictures.
When recruiting for the raptor monitoring volunteer program, the Longmont staff
will reach out to residents in various ways. The first method is flyers that are posted
around Longmont and brought to city-sponsored community events, like Longmont’s
Rhythm on the River, which happens each summer. The second is email outreach on
local list-servs such as the Boulder County Nature Association. Lastly, current
volunteers that are registered on Volgistics, the software that the volunteer coordinator
used for summer 2015 to manage and recruit volunteers, are contacted via a monthly
newsletter that lists the upcoming volunteer opportunities. The newsletter also details
how volunteers can sign themselves up for these one-day or multiple day events.
For the raptor monitoring volunteer program, City of Longmont staff train the
volunteers individually on the specific nest(s) that they are assigned to. Volunteers
receive a raptor monitoring handbook that provides them with information and
photographs on fledgling development, so that while the chicks are developing, the
volunteers can estimate how old they are. The handbook also describes safe practices
while observing, including bringing proper footwear and plenty of water. Along with the
handbook, City of Longmont staff would train a volunteer on a nest by bringing them to
the nest site. That way the volunteers learn how to identify the nest with the guidance of
staff members who are available to answer any questions they may have. This also
develops a connection between the staff member and the volunteer so the volunteer
would be more comfortable communicating with Open Space staff if any questions come
up after the training. Observation points for each nest have already been pre-determined
19
by City of Longmont staff members. The volunteer is shown where their specific
observation point for viewing each nest is, so that way monitoring occurs far enough
away from the nests that the breeding pair and chicks will not be disturbed by a
volunteer’s presence.
The completed volunteer forms are emailed to an Open Space staff member. The
raptor monitoring forms are then organized into folders on the Natural Resources server.
The 2012-2014 staff and volunteer raptor monitoring forms had already been input into a
yearly excel spreadsheet. I took all the forms from 2015 and input the information into a
2015 spreadsheet. I then compiled all the data from 2012-2015 and created a master
spreadsheet. From there, I went through the approximately 1,300 observations and
created a master summary data sheet of the 70 raptor nests. I also determined the number
of volunteers and the total observation time for each year. I will utilize all of this
information to determine the reproductive success of the seven raptor species monitored
in Longmont, Colorado.
20
Figure 3.1. Completed City of Longmont Raptor Monitoring Volunteer Form
Site Description
According to the 2010 Census, the City of Longmont, Colorado has a population
of about 86, 270. Longmont was founded in 1871 and is currently 27.6 square miles. It
is the 13th largest city in Colorado and includes the first new urbanist development
(Prospect New Town) in the state. Longmont continues to expand and develop; the city
21
is especially focusing on incorporating the tech industry whenever possible to provide
more jobs for its residents. There are twenty-six public parks scattered throughout the
city for people and wildlife to enjoy.
Development History of Longmont
Ian Colby, a city planner for the City of Longmont, provides a synopsis of
Longmont’s history and development:
Longmont [was] originally envisioned as a farming community, the arid climate
required an extensive ditch system to bring the water to the crops. The waters
from the mountains to the west would rush down during the spring, filling the St
Vrain and Left Hand Creeks as they flowed east into the plains below. Man [-]
made ditches diverting from these creeks would then irrigate the crops.
Originally, the town was subdivided over a square mile with a Main Street
running up the middle. The site was carefully chosen so that the St Vrain River
and the future railroad ran on the south side of this square. As the agricultural
economy of Longmont grew, the St Vrain Creek attracted the attention of a more
industrialized agricultural economy. Various canneries, mills, and train depots
deposited themselves on the edge of the St Vrain to take advantage of the water it
provided for industry. […] The Longmont site was chosen because the nearby
town of Burlington, directly on the river, had been virtually eradicated by a flood
a couple years before [.]
The flood of 2013 has spawned two big developmental plans for the City [:]
First, the Public Works department has undertaken […] massive projects to
"channelize" the St Vrain, trying to increase the flow as it moves down the river
rather than halting anywhere within the City limits and flooding the City again.
The City Manager's office, in conjunction with City Planning's update to the City
Comprehensive Plan, is also trying to revamp the St Vrain River by converting it
away from a decaying industrial area and into a walkable, open space/mixed use
area.
Development in the City continues to be focused mainly on further suburban
detached home development in the SW part of town (near the major employment
parks and Boulder) and on developing as much affordable apartment housing as
can be approved […]
As we're moving into the future, we obviously want a more walkable and less
zoned City with more development of housing; open space, especially along our
ditch greenways and "greenbelt" surrounding the City is valued by the Citizens a
22
great deal; there's no market for commercial or industrial in the City; and our
Public Works department continues to focus on preventing another flood.
Great Colorado Flood of 2013 Infrastructure Damages to Longmont
The City of Longmont’s Public Works and Natural Resources Department
calculated the major damages to the city from the Great Colorado Flood of September
2013 to be as follows:
Storm Drainage
Water Utility
Parks, Trails, Greenways
Street System, Bridges
Sewer Utility
Electric Utility
Fleet Infrastructure
Twin Peaks Golf Course
$90 million
$25.5 million
$20 million
$4 million
$2.6 million
$840, 000
$350, 000
$250, 000
The total damage inflicted on the City of Longmont by the Great Colorado Flood of 2013
was $148 million.
23
Figure 3.2. City of Longmont Bike Map, Courtesy of the City of Longmont
Figure 3.3. Greenways in the City of Longmont, Courtesy of the City of Longmont
24
Determining Which Species to Include in this Study
Nine raptor species are represented in the City of Longmont Raptor Monitoring
Dataset: Bald Eagle, Osprey, Great Horned Owl, Barn Owl, Red-Tailed Hawk, Cooper’s
Hawk, Swainson’s Hawk, Northern Harrier (also known as the Hen Harrier) (Circus
cyaneus), and Burrowing Owl (Athene cunicularia). Though there are nine species total,
not all of them have been monitored enough to be able to answer the research questions
in my study. The Burrowing Owl only has one observation in the data set, which means
there was only one observation during one season, so it would not be sufficient to answer
any changes in reproductive success or nest density. The Northern Harrier was never
observed to have chicks successfully fledge and had the second fewest total observations.
Due to the lack of observations, I will not be comparing the Northern Harrier or the
Burrowing Owl to the other seven raptor species, and I am not including these species in
the overall analysis. The other seven species were observed to have fledged chicks at
some points during the four years of study.
Differences Between Monitoring Years
Over the four years of monitoring, staff and volunteers may accumulate a better
understanding of which nests are active and where to look for the adult pairs that may be
nesting at each location. Due to this factor, it is possible that more adult pairs are being
accounted for, since there is continuing knowledge of these nests. Volunteers who
monitor the raptors for more than one season could also have a better eye for tracking the
raptors and taking notes on the behaviors of the adults and chicks. Nests found in future
nesting seasons could contribute to the data of the following years of raptor
monitoring. This increase in monitored nests each year also causes the number of
25
fledged chicks and pairs monitored to be higher than previous years. Another way that
the data could be impacted by volunteers is if the volunteer stopped observing the nest in
the middle of the season or if their notes are sparse or incomplete. Though the addition
of newly discovered nests or an increase in the number of volunteers may not be
consistent; it is most important that the raptors are being sufficiently monitored.
Figure 3.4. Nest Minutes/Hours Observed Per Year from 2012 to 2015
Geographic Information Systems (GIS)
The City of Longmont Open Space staff provided me with a GIS layer that
included all of the raptor nests in Longmont, Colorado, whether they were active or not.
I used the global positioning system coordinates of each nest to accurately pinpoint their
locations on the GIS layer. These points were especially important in answering the nest
density research question.
26
For the nest densities, I marked the locations of the active nests for all four years
of monitoring for four species in the data set. These species were the Bald Eagle, Great
Horned Owl, Osprey, and Red-Tailed Hawk. For each active nest of a species, I
measured the nearest two nests. I chose to measure the nearest two nests, since many of
the nests are along creeks or waterways and the nearest two nests are often the nests on
either side of the creek. I measured the nearest two nests whether they were occupied or
not.
I did not include any GIS maps or screenshots of the nest location map in my
thesis, since this could potentially compromise the safety of the nesting raptors in
Longmont. If a map of the nest locations were to be released, there is a possibility that
people may find the nests and disturb the raptors.
27
Chapter 4: Raptor Species Nesting Behaviors
Bald Eagle (Haliaeetus leucocephalus)
As our national bird, the Bald
Eagle is a widely recognized
American symbol. Bald Eagles
are frequently featured on nest
cams, and often the general public
will tune in to watch the adults
take care of their chicks. Bald
Eagle populations are still recovering from the effects of the usage of the chemical
dichlorodiphenyltrichloroethane (DDT), and though their numbers are steadily
increasing, it is still vital to monitor their population stability.
Once an adult Bald Eagle pair establishes a territory and builds a nest, they
commonly return to the same territory every year, even if the habitat quality has been
compromised or resources are limited (Stokes and Stokes, 1989). In those cases, the pair
will occupy the territory, which ranges from about half to two miles, during nesting
season, but will not breed (Stokes and Stokes, 1989). This could potentially have a
negative impact on the Bald Eagle population in the immediate area, especially if the pair
does not breed for multiple years in a row. Even if the pair do have chicks, if resources
are limited, then the oldest chick may be the only one to survive the nesting season
(Stokes and Stokes, 1989). A natural disaster, such as a major flood, could possibly
cause damage to a Bald Eagle’s territory and change their local habitat.
28
Along with habitat quality and prey availability, people can disturb a Bald Eagle
nest if they venture too close to the nest location. Bald Eagles prefer isolation from
people and will leave their nests if people come near. When the adult Bald Eagles fly
from the nest, the chicks become exposed to the current weather conditions and are not as
protected from other threats as well. Curious passersby often take pictures of these
magnificent eagles, but usually do not realize that they are putting the chicks in
danger. While City of Longmont raptor monitoring volunteers are observing the nest(s)
that they are assigned to, they also look out for any people who may be approaching
raptor nests. If someone is getting too close to a nest, the volunteer will ask them to keep
their distance from the nest and explain why it is important to do so. The volunteers
write down these instances in their raptor monitoring observation form.
Another important part of a Bald Eagle’s ability to successfully nest is the
proximity of the nest to water. Bald Eagles primarily feed on fish, so close proximity to
water allows them to provide for their chicks without expending too much energy.
Osprey (Pandion haliaetus)
Unlike Bald Eagles, Ospreys do not mind human presence.
The Ospreys in Longmont commonly nest in urban
environments, like golf courses or suburban
neighborhoods. Nest 5 is located in the Twin Peaks Golf
Course on the Westside of Longmont. The Osprey nest is
on top of a light pole on one end of the golf course. The
elevation of the nests keeps the chicks safe from predators
that reside on the ground. Ospreys primarily feed on fish and live near waterways. They
29
prefer shallow waterways, since they cannot dive more than about three feet below the
water’s surface (Poole, 1989). Ospreys nest within twelve miles of accessible fishing
since their diet is about 99% fresh or salt water fish (Poole, 1989). They live for about
15-20 years (Poole, 1989). The success of Osprey chicks is heavily reliant on the
availability of resources. Osprey chicks will often hatch days apart and a clutch will
typically be about one to four chicks (Poole, 1989). When food is readily available, the
chicks will share the food, but when resources are scarce, the oldest chicks often
dominate the younger chicks and the younger chicks will sometimes starve to death
(Poole, 1989). This life history characteristic is especially worrisome in the face of
natural disaster since resources may be compromised by the disaster event.
Red-Tailed Hawk (Buteo jamaicensis)
Red-Tailed Hawks are year-long residents
throughout most of the United States. They are
generalists that are often found soaring above
open habitats. Red-Tailed Hawks hunt for
mammals and are also known to consume other
birds and snakes (Blumstein, 1989). The adult
Red-Tailed Hawk pair will build the nest together in about a week (Blumstein, 1989).
The nest is often placed at the top of a tree, though Red-Tailed Hawks have been known
to sometimes place their nests on anthropogenic structures (Blumstein, 1989). RedTailed Hawks have a clutch size of about one to five eggs (Blumstein, 1989). A RedTailed Hawk pair will often return to a nest they had already built, unless a Great Horned
30
Owl or other raptor species is in the nest. If the previous nest is occupied, the Red-Tailed
Hawk pair will construct a new nest (Blumstein, 1989 and Stokes and Stokes, 1989).
Great Horned Owl (Bubo virginianus)
Great Horned Owls do not build their
own nests and this species relies on the
already built nests of other hawks in
order to have chicks (Olendorff, 1973
and Stokes and Stokes, 1989). Great
Horned Owls frequently use RedTailed Hawk nests. The Great Horned
Owls often nest before Red-Tailed
Hawks do and this nesting behavior
usually will not affect the reproductive
success of the Red-Tailed Hawks (Olendorff, 1973 & Stokes and Stokes, 1989). If Great
Horned Owls or Red-Tailed Hawks start nesting at different times it can potentially
impact the population stability of either species.
Barn Owl (Tyto alba)
The Barn Owl is a nocturnal raptor that feeds on small mammals
like rats. Since they are nocturnal, it is more difficult to track
their populations compared to other diurnal raptors. Barn Owls
will hunt several prey items and store them at the nest before the
chicks hatch. Barn Owls usually have a clutch of at least two
31
eggs and can have up to about eleven eggs (Bunn, Warburton, and Wilson, 1982). Barns
Owls utilize both natural and anthropogenic structures to build their nests. Barn Owls
often reuse nests that have already been built, and the Barn Owl adult pairs do not always
return to the same nest every year, but may end up using a different nest built by a
different pair of Barn Owls a year or more prior to that nesting season (Bunn, Warburton,
and Wilson, 1982). Barn Owls have been known to nest in close proximity, but will
often fly great distances to find prey items, especially if resources are scarce that year
(Bunn, Warburton, and Wilson, 1982). Since they primarily feed on small mammals, the
owls are not as reliant on a nearby water source like an Osprey or Bald Eagle pair would
be.
Cooper’s Hawk (Accipiter cooperii)
Cooper’s Hawks primarily feed on medium sized
avian species like Mourning Doves or European
Starlings (Jones, 1989). Cooper’s Hawks that live
in the west will also eat small mammals (Jones,
1989). They prefer forest environments, but can
sometimes be found in suburbs as well. Males will build the nest in about two weeks
(Jones, 1989). The clutch size is usually about two to six eggs (Jones, 1989). Cooper’s
Hawks prefer to build their nests in trees and the nests are usually high up in the trees.
32
Swainson’s Hawk (Buteo swainsoni)
Swainson’s Hawks primarily feed on
rodents, reptiles, rabbits, and insects
(Olendorff, 1973). In late Fall, they will
migrate from the lower 48 states to winter
in Argentina (Olendorff, 1973). Since
Swainson’s Hawks migrate long distances,
their diets can vary depending on what
resources are available in the region they are currently in (Olendorff, 1973). They prefer
open landscapes and nesting in trees, though they will sometimes use anthropogenic
structures like telephone poles. Swainson’s Hawks have also been known to dislocate
Red-Tailed Hawks that try to nest in a nest that was originally built by Swainson’s
Hawks (Olendorff, 1973). The Swainson’s Hawks may have just been starting to leave
the United States when the flood of 2013 hit Colorado in early September.
33
Chapter 5: Results and Discussion
1. Research Question
The main research question for this thesis is: How have raptor populations in
Longmont been impacted by the Great Colorado Flood of September 2013? One subquestion is: What was the reproductive success of each of the raptor species monitored in
Longmont, Colorado from 2012-2015? Another sub-question is: What is the approximate
nest density of the Bald Eagle, Great Horned Owl, Osprey, and Red-Tailed Hawk nests in
Longmont, Colorado?
Since there are two years of data collected before and after the flood, the data
informs the research question. The data can tell us what species occupied a nest during a
particular year and whether or not the pair had chicks. If the pair did have chicks, the
data can show whether the chicks fledged or failed that year.
This chapter presents the results of this thesis in various sections. The first
section addresses the reproductive success of raptors in Longmont, Colorado by year.
The second section details the changes in nest occupancy and account for the nest failures
that appear in the data set. Change in nest occupancy is when a nest is occupied by a
different species in the next nesting season. Nest failure is when the chicks successfully
hatch, but perish before they are fully grown. For the third section, I measured the nest
densities of the Bald Eagle, Great Horned Owl, Osprey, and Red-Tailed Hawk nests in
Longmont using Geographic Information Systems software. To evaluate whether
increased monitoring efforts are responsible for observed increases in raptor population, I
calculated the minutes observed per nest and include a table with the minutes per year.
The measurement of monitoring effort is important because the results may be skewed
34
towards the 2015 monitoring year, since almost half of the observations are from that
nesting season. I conclude with an assessment of how the raptors responded to the
September 2013 flood event. I discuss what has been previously reflected in the
literature and how these results align with other natural disaster and raptor studies.
2. Reproductive Success
Reproductive Success is when a species has viable offspring. A fledged chick is
when a chick is successfully able to leave a nest and subsist on its own. The sections in
this chapter show chicks fledged per each year of monitoring. The results of chicks
fledged per species are included in the Appendix.
3. Raptor Populations and the Flood of September 2013
Results
After the Great Colorado Flood of September 2013, the monitoring data suggests
that Longmont’s raptor populations have not been negatively affected by this flood. The
number of overall fledglings either stayed stable or grew tremendously. Monitoring for
reproductive success allows the City of Longmont to gauge the population size of raptor
species in the area. Great Horned Owl, Osprey, and Red-Tailed Hawk populations
displayed a positive trend over the four years. Bald Eagle populations were stable
throughout the four years. The three other species, Cooper’s Hawk, Swainson’s Hawk,
and the Barn Owl, did not have enough fledglings to show a significant difference
between populations before and after the flood.
Overall, the number of successfully fledged raptor chicks is increasing over time.
In 2012, 22 chicks fledged. In 2013, eight more chicks fledged than the previous year,
with 30 successful chicks total this year. In 2014, the overall number of chicks fledged
35
jumped by 17 chicks for a total of 47. In 2015, 67 raptor chicks successfully fledged,
which was an increase of 20 from the previous nesting season. Over the four years of
monitoring, raptor populations in Longmont appear to be either stable or growing.
Discussion
The raptors have been resilient to the Great Colorado Flood of September 2013
and it can be inferred that none of the raptor species populations are dropping after the
flood. This conclusion reflects the literature on natural disasters and their impacts on
raptors. In the literature, raptors are often resilient after facing sudden natural disasters,
like strong wind storms (Martinez et al., 2013 and Pentarini et al., 2002). The raptor
populations in Longmont are likely stable or increasing and the flood does not seem to
have negatively impacted their populations.
36
Figure 5.1. Number of Fledglings per Year per Species from 2012-2015
4. Chicks Successfully Fledged by Year
Chicks Successfully Fledged in 2012
Species
Nest Number
Number of Fledged
Chicks
Barn Owl
13
4
Red-Tailed Hawk
4, 7, 9, 18, 21
8
Osprey
6, 15, 19
7
Bald Eagle
8, 10
3
Table 5.1. Chicks Successfully Fledged in 2012
In 2012, there was a total of 22 fledglings that were monitored in 15 different
nests. Four species: Barn Owls, Red-Tailed Hawks, Ospreys, and Bald Eagles had
37
fledglings. There were four Barn Owl fledglings, eight Red-Tailed Hawk fledglings,
seven Osprey fledglings, and three Bald Eagle fledglings. For Barn Owls, there were
four fledglings in Nest 13. For Red-Tailed Hawks, Nests 4 and 21 each had one chick
and Nests 7, 9 and 18 each had two chicks. For Ospreys, Nest 6 had three chicks. Nests
15 and 19 had two chicks each. For Bald Eagles, Nest 8 had one chick and Nest 10 had
two chicks.
Chicks Successfully Fledged in 2013
Species
Nest Number
Number of Chicks
Fledged
Red-Tailed Hawk
4, 9, 20, 21, 25, 33, 34, 36,
38, 39
18
Great Horned Owl
22, 26, 30, 35, 41
7
Osprey
6
3
Swainson’s Hawk
27, 37
2
Table 5.2. Chicks Successfully Fledged in 2013
In 2013, there was a total of 32 raptor chicks monitored that successfully fledged.
There were 26 active nests. These nests were active, but not all of them successfully had
chicks. This was also the first year that Swainson’s Hawks and Great Horned Owls had
chicks fledging in this data set. Four species had chicks this year.
Overall there were 18 Red-Tailed Hawk chicks, seven Great Horned Owl chicks,
three Osprey chicks, and two Swainson’s Hawk chicks. For Red-Tailed Hawks, Nest 4
and 36 had one chick. All of these nests had two chicks each: Nest 9, 20, 21, 25, 33, 34,
38, and 39. For Great Horned Owls, Nest 22, Nest 26, and Nest 35 each had one chick.
38
Nest 30 and 41 had two chicks each. For Ospreys, Nest 6 had three chicks. For
Swainson’s Hawks, Nests 27 and 37 had one chick each.
Chicks Successfully Fledged in 2014
Species
Nest Number
Number of Chicks
Fledged
Red-Tailed Hawks
3, 4, 9, 17, 20, 21, 25, 29,
26
33, 34, 45, 47
Osprey
2, 5, 6, 19
8
Great Horned Owl
22, 42, 43, 44
7
Bald Eagle
8, 10
4
Swainson’s Hawk
14
2
Table 5.3. Chicks Successfully Fledged in 2014
Since the Great Colorado Flood of September 2013, the results found in the last
two years of monitoring depict what happened to the raptor populations after the impact
of the flood. In 2014, there was a total of 47 chicks monitored that successfully fledged.
There were 28 active nests in 2014. There were 26 Red-Tailed Hawks. There were eight
Osprey chicks, seven Great Horned Owl chicks, four Bald Eagle chicks, and two
Swainson’s Hawk chicks. Five species had chicks in 2014. For the Red-Tailed Hawks,
Nests 3, 20, and 45 each had three chicks. Nests 4, 9, 17, 21, 25, 33, 34, and 47 each had
39
two chicks. Nest 29 was the only Red-Tailed Hawk nest that had one chick that year.
For Ospreys, Nests 2, 5, 6, and 19 each had two chicks. For Great Horned Owls, Nests
22 and 42 each had one chick. Nest 43 had three Great Horned Owl chicks. Nest 44 had
two chicks. For Bald Eagles, Nest 8 and Nest 10 had two chicks. For Swainson’s
Hawks, Nest 14 had two chicks.
Chicks Successfully Fledged in 2015
Species
Nest Number
Number of Chicks
Fledged
Red-Tailed Hawk
3, 21, 22, 25, 32, 33, 36,
21
51, 65
Great Horned Owl
12, 40, 42, 44, 47, 49, 66,
18
67
Bald Eagle
10, 58
4
Cooper’s Hawk
68
2
Osprey
4, 5, 6, 17, 19, 26, 50, 54
22
Table 5.4. Chicks Successfully Fledged in 2015
In 2015, there were 67 total raptor fledglings. There were 42 active nests in 2015.
There were 22 Osprey chicks. There were 21 Red-Tailed Hawk chicks. Great Horned
Owl chick numbers increased from seven in 2014 to 18 in 2015. There were four Bald
40
Eagle chicks and two Cooper’s Hawk chicks. There were five raptor species that had
chicks in 2015. For the Ospreys, Nests 4, 19, 26, and 50 each had three chicks. Nests 5,
17, and 54 each had two chicks. Nest 6 was the only Osprey nest that had one chick. For
Red-Tailed Hawks, Nests 3 and 51 each had one chick. Nests 21, 25, 33, 36, and 65 each
had three chicks. Nests 22, 25, and 32 each had two chicks. For Great Horned Owls,
Nests 12, 40, 42, and 49 each had two chicks. Nests 44, 47, and 66 each had three chicks.
67 was the only Great Horned Owl nest that had one chick in 2015. For Bald Eagles,
Nests 10 and 58 each had two chicks. For Cooper’s Hawks, Nest 68 had two chicks and
is the only nest that successfully had chicks for this species in the entire data set.
5. Nests Observed for all Four Years
Since nests were discovered later in the data set, I calculated the number of chicks
that fledged in the nests that were observed from 2012 to 2015. The number of chicks
increased per year over the four years of monitoring. In 2012, 19 chicks fledged. In
2013, 20 chicks fledged. In 2014, 36 chicks fledged. In 2015, 40 chicks fledged. The
numbers for 2012 and 2013 are similar to each other and the 2014 and 2015 are closer to
each other, which could possibly show that populations increased after the flood. The
observation minutes still apply and may skew the results. This analysis helps to eliminate
the variable of nests that were observed for less than four nesting seasons.
41
Figure 5.2. Fledgling Success in Nests Monitored for Four Years
6. Nest Failures from 2012 to 2015
Nest Failure by Species
From 2012 to 2015, there was a total of 23 failed nests. Nests 2, 5, 7, 8, 10, 15,
17, 23, 26, 36, 37, 43, 45, 55, 61, 63, 64, and 69 failed at least once. Barn Owls were the
only species that did not have a failed nest. Ospreys had eight failed nests over 4 years,
which is the most failed nests compared to the other six species in the
study. Though there were eight times Osprey nests failed, those failures were in the same
three locations. Four out of the eight Osprey chick failures were from Nest 2, which
failed every year it was monitored by Longmont volunteers. Nest 2 should be a nest of
concern for the City of Longmont staff since it is the only nest in the entire dataset that
failed every year it was monitored. Nest 5, which was consistently occupied by Ospreys,
42
failed in 2012 and 2013. Osprey Nests 15 and 61 failed in 2015. Red-Tailed Hawks
had five nest failures. Nests 17, 26, 45, 55, and 69 failed once. Nest 17 failed in
2013 and Nest 26 failed in 2014. Additionally, Nests 45, 55, and 69 failed in
2015. Cooper’s Hawks had two nest failures. Cooper’s Hawk Nests 63 and 64 failed in
2015. Swainson’s Hawks only had one nest failure (Nest 37) in 2013. Great Horned
Owls had three nest failures. Nests 7, 36, and 43 failed once. Nest 7 failed in 2013, Nest
36 failed in 2014, and Nest 43 failed in 2015. There were no Great Horned Owl
fledglings in 2012 and no nest failures were documented for that year. Bald Eagles
had two nest failures. Nests 8 and 10 failed in 2013 and there were no juvenile Bald
Eagles in 2013. There were notes on volunteer raptor monitoring observation forms that
indicated a major snowstorm in April. The snowstorm may have been the primary factor
for Bald Eagle nest failures in 2013.
Nest Failure by Year
In 2012, both Eagle Nests 2 and 5 failed and were occupied by Osprey. In 2013,
Osprey, Great Horned Owls, Bald Eagles, Red-Tailed Hawks, and Swainson’s Hawks
all experience at least one nest failure. A total of eight nests failed in 2013 (Nests 2, 5, 7,
8, 10, 17, 23, 37). In 2014, three nests failed (Nests 2, 26, and 36). One nest failed from
each of these three species: Osprey, Great Horned Owl, and Red-Tailed Hawk. In
2015, nine nests failed (Nests 2, 15, 43, 45, 55, 61, 63, 64, and 69). Osprey, Great
Horned Owl, Red-Tailed Hawk, and Cooper’s Hawk species had at least one nest fail that
year.
43
7. Nest Occupation Changes from 2012 to 2015
Changes in Species in Each Nest
There were ten instances where nest locations were used by more than one species
of raptor during different nesting seasons. There were four times that a nest was
occupied by a Red-Tailed Hawk pair one year and then by an Osprey pair the next year.
This happened with Nests 4, 17, 20, and 26. There were two times that a nest was
occupied by a Red-Tailed Hawk pair one year and then by a Great Horned Owl pair the
next year. This happened with Nests 7 and 47. There were four times that a nest was
occupied by a Great Horned Owl pair one year and then by a Red-Tailed Hawk pair the
next year. This happened with Nests 22, 26, 32, and 36.
Nests that were Consistently Occupied by the Same Species
For nests that were monitored all four years, from 2012 to 2015, six nests were
consistently occupied by the same species. Nests 2, 5, and 6 were always occupied by an
Osprey pair. Nest 10 was always occupied by a Bale Eagle pair. Nests 21 and 25 were
always occupied by a Red-Tailed Hawk pair. Accounting for all four years of
monitoring, there were four nests that were never occupied by any raptors. Nests 1, 11,
16, and 24 were never occupied and staff quickly observed them to check if any adult
pairs were seen in the nest that season.
Changes in Nest Occupation
The main species that saw changes in nest occupations every year were the Great
Horned Owls, Red-Tailed Hawks, and Ospreys. Great Horned Owls and Red-Tailed
Hawks commonly nest at different times and Great Horned Owls will take the nests of
Red-Tailed Hawks (Stokes and Stokes, 1989). The main change in nest occupation that
44
is not as common of an occurrence is the number of Ospreys that occupy Red-Tailed
Hawk nests. This is a particularly interesting result since it is not reflected in bird
behavior literature and could possibly be due to the changes in waterways in Longmont
after the Great Colorado Flood of September 2013.
8. Nest Densities for BAEA, GHOW, OSPR, and RTHA
Nest proximities are an important factor to look at since the raptors in the data set
are territorial and could be impacted by other raptors that may be nesting too close by.
This would also increase the level of competition for prey near the nests if the raptors
share the same preference for prey.
Nest Density for Bald Eagles
Bald Eagle Nest Number
Nearest Nest in Miles #1
Nearest Nest in Miles #2
8
0.07
0.1
10
0.18
0.22
58
0.12
0.1
Average Miles: 0.131
Table 5.5. Bald Eagle Nest Density, Nearest Two Nests
The raptor nests closest to the Bald Eagle nests are all within 0.2 of a mile away
from the Bald Eagle nests. The Bald Eagle nests were about 1-3 miles away from each
other. Bald Eagles need at least about half a mile during the nesting season and all of the
Bald Eagle nests in Longmont are at least about a mile apart from each other (Stokes and
Stokes, 1989). Kralovec et al. (1992) found that over nine years of monitoring Bald
45
Eagles in Colorado and Southeastern Wyoming, reproductive success was not
compromised by the nest density of the Bald Eagles being monitored in this study.
Nest Density for Great Horned Owls
Great Horned Owl Nests
Nearest Nest in Miles #1
Nearest Nest in Miles #2
7
0.51
0.85
12
0.36
0.37
22
0.44
0.41
26
0.02
0.22
30
0.1
0.16
32
0.04
0.18
35
0.22
0.25
36
0.44
0.58
40
1.12
1.4
41
0.58
0.68
42
0.02
0.24
43
0.01
0.03
44
0.22
0.44
47
0.19
0.13
49
0.06
0.74
66
2.54
2.34
67
0.03
0.05
Average Miles: 0.469
Table 5.6. Great Horned Owl Nest Density, Nearest Two Nests
46
Great Horned Owls nest in clusters around the city and many of the nest numbers
are very close to each other because of this. Great Horned Owls are nest predators and
rely on the already built nests of other raptors to have successful chicks during a nesting
season.
Nest Density for Ospreys
Osprey Nest Number
Nearest Nest in Miles #1
Nearest Nest in Miles #2
2
0.05
0.06
4
0.99
0.73
5
0.65
0.73
6
0.92
0.85
15
0.82
0.75
17
0.16
0.46
19
0.46
0.44
20
1.55
1.52
26
0.02
0.22
50
0.16
0.55
54
0.64
0.67
61
1.2
1.22
Average Miles: 0.659
Table 5.7. Osprey Nest Density, Nearest Two Nests
47
Some of the Osprey nests, like Nest 20, were over a mile away from other nests.
This is primarily due to the Osprey pair’s ability to tolerate human presence. Other
raptors prefer not to have their nests in urban areas and instead will choose trees next to a
creek.
Nest Density for Red-Tailed Hawks
Red-Tailed Hawk Nest
Number
Nearest Nest in Miles #1
Nearest Nest in Miles #2
3
0.03
0.06
4
0.73
0.99
7
0.51
0.85
9
0.1
0.15
17
0.16
0.46
18
0.94
1.08
20
1.55
1.52
21
0.15
0.41
22
0.44
0.41
23
0.04
0.13
25
0.11
0.18
26
0.02
0.22
28
0.87
1.32
29
0.16
0.68
32
0.04
0.18
33
0.18
0.22
34
0.68
1.22
36
0.58
0.44
38
0.61
0.6
48
39
0.35
0.55
45
0.44
0.44
47
0.19
0.13
51
1.03
0.98
55
0.22
0.28
65
0.32
0.35
69
0.01
1.39
Average Miles: 0.494
Table 5.8. Red-Tailed Hawk Nest Density, Nearest Two Nests
There is some overlap between nest numbers from nests that were used by both
Red-Tailed Hawks and Great Horned Owls depending on the year of occupancy. RedTailed Hawks had a higher number of nest locations compared to the other six raptor
species in the data set.
49
9. Observation Time Per Nest from 2012 to 2015
Figure 5.3. Observation Minutes and Hours by Longmont Staff and Volunteers
The purple line between the Year 2013 and the Year 2014 represents the flood event.
This table depicts the number of minutes observed per nest by staff and volunteers
over the four years of monitoring. I went through the raptor monitoring data sheet for all
four years and calculated the total number of minutes each nest was observed. There are
70 nests total and not all of them were observed every year. Many of the nests were
discovered and monitored after 2012. Only 22 nests were observed in 2012. There are
only zeros in the 2012 column after Nest 26 because those nests were slowly added later
in the raptor monitoring program. In 2013, 33 nests were monitored. In 2014, 42 nests
were monitored. In 2015, 62 nests were monitored. Nest 70 is the only nest that has
50
never been monitored. Nest 70 is in the attribute table of the Geographic Information
Systems City of Longmont Open Space raptor nest locations layer.
There is a wide variety of minutes represented in Table 5.9. Over the four years,
Nest 53 only had two minutes’ worth of observations made on the nest, which was the
lowest out of Nests 1 to 69. Over the four years, Nest 2 was observed for about 3, 924
minutes, which makes it the most observed nest out of the entire dataset. This nest was
occupied by an Osprey pair all four years, so the nest was observed all season throughout
the dataset.
The variety in nest observation times may occur for a few reasons. The nests that
were observed for 20 minutes or less that season, are often nests that City of Longmont
staff members periodically checked on for a few minutes in order to determine whether
the nest is active or not that season. City of Longmont staff will usually observe a nest
for about five minutes to determine whether it is active or not. Another reason for the
variety in nest observation times are whether that nest is active or not. If a nest is active
and a volunteer is assigned to watch that nest, then the nest should be monitored at least
30 minutes a week from when they are assigned to when the chicks fledge. Some
volunteers will choose to watch nests for more than 30 minutes a week. Usually when a
volunteer is unable to watch a nest for a week for any reason, they reach out to the City of
Longmont staff so that way a staff member or another volunteer can cover that particular
nest for that week. There are also times when the nests do not get watched at all,
especially if a volunteer stops communicating with the City of Longmont staff or
submitting their observation forms. These numbers can also explain differences between
51
nests if statistics are run on the data. It may be able to account for outliers that may occur
due to the very different observation times each season.
52
Minutes Observed Per Nest from 2012 to 2015
Nest #
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
Overall
6
3924
1694
847
1901
4158
258
446
254
1051
6
41
377
144
87
51
1357
63
1991
2015
160
99
36
12
199
854
298
30
56
47
12
44
133
172
10
67
2012
5
175
5
66
54
211
81
178
91
82
6
15
323
30
72
27
10
55
122
45
44
0
0
0
15
0
0
0
0
0
0
0
0
0
0
0
2013
0
1035
8
68
660
869
130
205
103
287
0
0
25
8
0
0
409
7
521
888
37
48
0
0
100
291
248
2
8
30
15
39
52
10
40
76
2014
1
1570
688
27
591
986
17
58
20
49
0
1
9
97
0
6
369
1
572
317
44
10
6
0
52
16
25
0
38
5
0
6
46
115
0
12
2015
0
1144
993
686
596
2092
30
5
40
633
0
25
20
9
15
18
569
0
776
765
35
41
30
12
32
547
25
28
10
12
12
23
48
5
0
15
53
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
123
53
51
453
33
29
18
183
95
27
76
49
233
873
108
62
2
507
70
5
18
55
9
17
402
81
5
10
15
177
386
358
10
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
36
48
10
29
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
42
17
3
2
4
11
8
15
63
9
38
20
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
5
0
0
441
0
18
10
168
32
18
38
29
233
873
108
62
2
507
70
5
18
55
9
17
402
81
5
10
15
177
386
358
10
0
Table 5.9. Minutes Observed Per Nest from 2012 to 2015
54
10. Conclusion
The monitoring program has provided valuable information on the population
status of raptors in Longmont, Colorado. The data is potentially skewed towards an
increase in population over the four years due to the discovery of new nests and adult
raptor pairs that may have existed before the flood but were not monitored by volunteers,
since those nests had not been located or built yet. Along with the addition of new nests
to the data set, volunteers that return to do this monitoring will have a previously
acquired knowledge of where to look for the adult pairs and fledglings. This could make
it so more fledglings are being recorded in the most recent years of the program versus
when the raptor monitoring program first started in 2012. One way to keep account for
these variables is to only look at the population changes in nests that were recorded and
monitored all four years. Though this limits the sample size, it gives a fairer
representation of what the raptor population sizes would be in Longmont.
The carrying capacity and resource availability in the area play a role in the
population size. In the literature, raptor populations remained stable after wind storm
events knocked down trees that had raptor nests in them (Pentarini et al. 2012, Martinez
et al., 2013). Though it takes energy for these raptors to rebuild their nests for the nesting
season after a natural disaster, it is an endeavor that takes two weeks or less and the
raptors are usually un-phased if they need to construct a nest after the previous one is
destroyed. The data suggests that the raptors in Longmont, Colorado responded in a
similar manner.
55
11. Appendix: Reproductive Success by Raptor Species
The results of reproductive success for each raptor species has been placed in the
appendix. This section contains the same information as reproductive success by
monitoring year. The organization of the reproductive data will prove useful if data is
needed on what happened to a particular species rather than looking at overall trends by
year.
56
Chapter 6: Recommendations and Further Research
“…monitoring implies the need to determine change.”
–Frederic Hall (2002) Photo Point Monitoring Handbook
Recommendations: Photo Point Monitoring and Habitat Quality
Photo Point Monitoring, also known as repeat photography, is a cost-effective
method that captures visible change in a location over time. The technique involves
taking a photograph at the same location and angle every year, or every other year.
In this section, I demonstrate the ways that the raptor monitoring program could
benefit from the use of repeat photography in the landscapes near the raptor nests,
especially since habitat quality is an important factor towards the reproductive success of
raptor species. The City of Longmont already has established raptor and photo point
monitoring volunteer programs, so the two can be combined to create a better
understanding of the status of the local raptor populations.
Photo Point Monitoring has been previously used in a variety of different
landscape studies. Photo points have also been used to research a natural disaster. For
example, a 2013 study by Khan et al. used photo point monitoring to determine landscape
changes after an October 2005 earthquake in the Hazara-Kashmir region of northern
Pakistan.
The City of Longmont Open Space staff started using photo point monitoring
throughout the city in the summer of 2011. Photo points have been added each year since
then and the city now has over 200 photo points. These points capture the condition of
areas of interest that the city would like to monitor.
57
The photos are able to denote natural or anthropogenic changes across a series of
photos. For example, City of Longmont staff members could see if an invasive weed is
taking over a certain area and needs to be addressed. If urban development has expanded
within the area of a photo point, then it can visibly show the impact that man-made
structures have had on the immediate surroundings. For instance, a street light was added
to one of the bridges in Longmont and it shows up in the most recent photo point taken of
that location.
As the number of photo points in the city increased, Longmont staff decided to
start a Photo Point Monitoring Volunteer Program in the summer of 2015. As an intern
with the City of Longmont, Colorado’s volunteer coordinator that summer, I helped
create materials for this new volunteer program, led the volunteer training, and was the
point of contact for volunteers throughout the program. Much like the raptor monitoring
volunteer program, the spots for the photo point program filled up quickly and volunteers
were highly interested in learning more about this monitoring technique. By the end of
the summer, volunteers had contributed around 70 photographs that were put into the
City of Longmont’s online and hard copy databases.
Photo Point Monitoring is volunteer friendly, since it does not require expensive
equipment. This makes it an ideal technique for the organization running the program,
since it does not take much from their current budget or available resources. Volunteers
were asked to have their own digital cameras, while the city gave each volunteer a fourfoot PVC pipe so that all the photo points could be taken at the same height each time.
58
Photo Points and Raptor Nests
The raptor monitoring and photo point monitoring volunteer programs can
reinforce each other. Both programs utilize citizen science and connect the volunteers to
their local environment. Photo points that are already established around raptor nests can
be used to evaluate the habitat quality or change in waterways each year. The current
photo points have captured the changes caused by the Great Colorado Flood of
September 2013 and could potentially document the changes caused by future floods in
Longmont. New photo points could be established that capture the areas below or around
the raptor nests. These points will need to be established far enough away from the nests
that the raptors will not be impacted by the presence of a volunteer taking a photo.
Establishing a new photo point does not take much time. An Open Space staff
member will bring a digital camera, four-foot PVC pipe, and a GPS device (or a
smartphone with GPS capabilities) to document the new photo point. A photograph is
taken of an area of interest, the angle of the photo is documented, and then the GPS
coordinates are recorded onto a set of notes to be uploaded with the photo point once the
staff member returns from the field. The new photo point location information is entered
into a GIS layer to keep track of the many points throughout the city and maps to the
locations are created using GIS so a volunteer or staff member will have a guide to find
that particular photo point.
Raptor Nest Cameras
Boulder County has an Osprey nest camera set up at the Boulder County
Fairgrounds in Longmont, Colorado. Ospreys are an ideal raptor species to focus a
camera on since they are more tolerant towards human presence than other raptor species.
59
The Ospreys are live streamed and the footage is accessible to the public through the
Boulder County website.
The raptor monitoring volunteer program is a great way to engage the public and
create a connection between the volunteers and the raptors that they watch each week, but
this engagement only applies to volunteers in the program. Raptor nest cameras allow
the connection to be made with anyone who tunes into the livestream to watch the raptors
care for their chicks. Boulder County’s website includes information on when the male
and female adult Ospreys first arrived at the nest this season, the number of eggs that
have been laid in the nest, and the estimated date that the eggs will start to hatch. This
camera is a good resource for the public to recognize that these raptors are a part of the
Longmont community and that the Ospreys have chosen to make the Boulder County
Fairgrounds their home.
Further Research: Nest Density and Spatial Location
Raptor monitoring data can be used to answer a variety of different research
questions and this thesis delves into the reproductive success and population stability of
the raptors in the City of Longmont. Four more research questions that can be
determined using the City of Longmont raptor monitoring data are: What was the nest
density of raptor species before and after the flood? How has the spatial location of nests
changed? Is there a difference between the reproductive success of raptors that nest on
private versus publicly owned land? Is there a difference between the reproductive
success of raptors that nest in urban versus rural areas?
One of the ways this study could be a reference point is by analyzing nest density,
which is important for the reproductive success of raptor species. The nest densities in
60
the results chapter accounted for the nearest two nests for the four main species in this
study. Nest densities can be measured in other ways.
Most of the species in the data set are territorial and require an ideal amount of
quality habitat for their nest site. If a raptor pair return to a territory and the quality of the
habitat has been compromised, then the pair may not breed that year (Stokes and Stokes,
1989). Density of nests also affects the level of competition between raptor species,
especially when prey becomes scarce. The nest density and spatial location results could
help inform the knowledge and management of other areas similar to the landscape of
Longmont, Colorado. The particular spatial locations of nests by year could demonstrate
changes in how close the raptors are nesting to buildings or neighborhoods. Depending
on the raptor species, the proximity of a nest to urban areas could possibly influence
whether the raptors in the nest are consistently being flushed, which can lead to nest
abandonment. These changes could inform building expansion in the city because the
City of Longmont staff will have a better idea of what areas would potentially negatively
impact which raptor species. If there was a trend in a direction that nest occupation
shifted, then staff members could check those areas for new nests.
The City of Longmont raptor monitoring dataset can also be used to look at avian
species interactions. The volunteers take detailed notes on when avian species or humans
disturb the adults in the nest. The volunteers will write down what avian species comes
too close to a raptor nest and how the nesting adult raptors react to the intruder’s
presence. Volunteers can be encouraged to continue to document these interactions in
full. Volunteers are often able to identify the intruder by species, but if it is a species that
the volunteer is unfamiliar with, then the volunteer can write down some characteristics
61
of the other avian species that would help the staff identify what the other bird may have
been.
62
Chapter 7: Conclusion
“Over increasingly large areas of the United States, spring now comes unheralded
by the return of the birds, and the early mornings are strangely silent
where once they were filled with the beauty of bird song.”
– Rachel Carson, Silent Spring, 1962
Though all seven raptor species studied in this thesis are currently categorized as
Least Concern species by the International Union for Conservation of Nature, it is still
vital to keep track of their population status in case a species’ population starts dropping.
This is especially concerning if the number of individuals is dropping in a particular
region, which makes it important to look at raptor populations within city limits.
The populations of raptor species in this study have fallen in the past. Bald Eagle
populations in the United States were negatively impacted by the widespread use of DDT
and have only recently recovered from this devastating pesticide. Osprey populations
were also hard hit by DDT and Osprey populations have been steadily recovering since
the federal ban on DDT that was implemented in 1972. These birds of prey should be
continuously monitored so that if their populations start dropping again, a university,
non-profit, city staff, etc. can start looking into reasons that the population decline may
be happening.
Citizen science efforts are effective for tracking the reproductive success of
raptors in the City of Longmont, Colorado. Citizen science allows for the raptors to be
monitored for more minutes each season and the volunteer program creates a connection
with the community to the natural environment. This research is a result of the time
contributed by staff and volunteers and if other cities also have continuous raptor
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monitoring programs then the population stability of these raptor species can be
documented in as many locations as possible.
Since natural disasters are often unpredictable, monitoring efforts need to be
established before the natural disasters occur in order to compare changes and find trends
over time. After the Great Colorado Flood of September 2013, literature has been written
on the impacts of the flood on Boulder County communities, but not on its impacts on
wildlife in the area. Further research that could be completed with the raptor monitoring
data include nest density, spatial location, proximity to urban areas, and species
interactions. Further research could also help fill the gap in the literature when looking at
the impact of natural disasters on wildlife. This thesis provides a reference point for any
researcher who may be analyzing how a past or future natural disaster is impacting raptor
populations.
The nesting behaviors of the raptor species are necessary to keep in mind when
addressing population stability. Habitat quality is an important factor for whether or not
a raptor pair will have chicks during a particular nesting season. Photo point monitoring
could provide qualitative information on the changes in habitat quality near raptor nests
in Longmont.
With the increasing occurrences and impacts of natural disasters due to climate
change, it is more important than ever to look at the effects that each type of natural
disaster may leave on both communities and their environments. Flood events are
devastating to people and their infrastructure, and birds to and their habitats. The more
that is understood about climate change and how it effects all aspects of the environment,
the more prepared cities can be to manage their wildlife after a natural disaster.
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The populations of the raptor species studied in this thesis have declined before,
and raptor monitoring data using citizen science can play a vital role in ensuring it does
not happen again.
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Appendix
Reproductive Success by Species:
Bald Eagle
Three Bald Eagle chicks hatched during the first year of monitoring and four
chicks hatched for each of the last two years. In 2013, all of the Bald Eagle chicks failed
due to an April snowstorm. The adult pair in Nest 8 had one hatched chick that season
that did not survive the snowstorm. Two chicks hatched in Nest 10 and both of those
chicks did not survive the nesting season. There was a steady number of Bald Eagle
chicks, four a year, during the nesting seasons after the flood.
Three Bald Eagle chicks fledged in 2012. In 2013, no Bald Eagle chicks survived
the nesting season. In 2014 and 2015, four Bald Eagle chicks successfully fledged.
Though Nest 8 failed due to a snowstorm in April 2013, the Bald Eagle pair was
successfully able to have two chicks during the 2014 nesting season. The Bald Eagles
chicks were always in Nests 8 and 10, except for two fledglings that were in Nest 58 in
2015. Nest 8 was not observed in 2015.
Red-Tailed Hawk
The number of Red-Tailed Hawk chicks steadily increased for the first three years
of monitoring. The number decreased by 5 chicks in 2015. Since the decrease did not
occur until two nesting seasons after the flood, it is difficult to conclude whether the
flood was the direct factor in the decrease in Red-Tailed Hawk chicks that year.
Red-Tailed Hawk nests occur 45 times in the dataset. In 2012, eight chicks
fledged and none of the nests monitored that year failed. In 2013, eighteen chicks
fledged. Nests 17 and 23 failed. In 2014, 26 chicks fledged and Nest 26 failed. In 2015,
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21 chicks fledged. Nests 23, 45, 55, and 69 failed. Active Red-Tailed Hawk nests occur
the most in the dataset compared to the active nests of the other species.
Osprey
Four fewer Osprey chicks fledged between the 2012 to 2013 nesting season.
After the difference between those two nesting seasons, the number of fledged Osprey
chicks increased each year. The number of chicks almost tripled between 2014 and 2015.
Ospreys have been very successful after the flood and their populations could be
increasing.
24 active Osprey nests were monitored in the dataset. In 2012, seven chicks
fledged. In 2013, three chicks fledged. In 2014, eight chicks fledged. In 2015, the
number of Osprey chicks fledged jumped to 22. 8 Osprey nests failed throughout the
four years of monitoring. Nest 2 failed all four years. In 2014, the Osprey pair in Nest 2
had two chicks, but both the chicks failed. Nest 5 failed in 2012 and 2013, before the
flood event. The adult Osprey pair in Nest 5 had two successfully fledged chicks a year
for 2014 and 2015, which was after the flood event. In 2015, Nests 15, 54, and 61 also
failed. In 2012, Nest 15 had two fledged Osprey chicks. In 2015, after the flood event,
Nest 15 failed. In 2012 and 2013, Nest 6 had three fledged Osprey chicks each year.
After the flood event, the number of Osprey chicks fledged in that nest went down. In
2014, Nest 6 had two chicks. In 2015, Nest 6 had one chick. So though there were still
chicks fledging, the number of individuals has been decreasing since the flood.
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Great Horned Owl
There were no Great Horned Owl chicks in 2012, but since then their numbers
have been increasing. From 2014 to 2015, the number of chicks fledged more than
doubled. Great Horned Owl chicks have been thriving in Longmont in three out of the
four years of monitoring.
Great Horned Owl nests were monitored 23 times in the dataset. In 2012, no
Great Horned Owl nests were monitored. In 2013 and 2014, there were seven chicks that
fledged each year. In 2015, the total number of fledged Great Horned Owl chicks
jumped to eighteen. Three Great Horned Owl nests failed throughout the four years of
monitoring. In 2013, Nest 7 failed. In 2014, Nest 36 failed. In 2015, Nest 43 failed.
Cooper’s Hawk
Cooper’s Hawk chicks were not monitored until 2015. Two Cooper’s Hawk
chicks successfully fledged that year. The previous years there were no successfully
fledged Cooper’s Hawk chicks. Since Cooper’s Hawks only had chicks during one year
of monitoring, it cannot be determined whether their reproductive success was impacted
by the flood in 2013. Active Cooper’s Hawk nests were monitored three times in the
dataset. In 2015, Nests 63 and 64 failed, but Nest 68 had two chicks.
Swainson’s Hawk
Swainson’s Hawks had successful nests in 2013 and 2014. There were two
fledged chicks for both years of monitoring. There were no Swainson’s Hawk chicks
monitored in 2012 or 2015. Since this was the year before and the year after the flood, it
is difficult to tell whether the flood is the cause of the lack of Swainson’s Hawk chicks in
2015. Active Swainson’s Hawk nests were monitored four times in the dataset. In 2013,
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Nests 27 and 37 each had one chick. In 2014, Nest 14 had two chicks. In 2015, Nest 27
was occupied by an adult Swainson’s Hawk pair, but the dataset is unable to determine
whether the pair successfully had chicks or not.
Barn Owl
In the four years of monitoring, there was only one successful Barn Owl
pair. There were four chicks in 2012, then the number of chicks dropped to zero for the
next three years. Since Barn Owl populations dropped the nesting season before the
flood hit Longmont, it is difficult to determine whether the flood was the main factor in
why the Barn Owl populations have not been seen in Longmont for the past few nesting
seasons. An active Barn Owl nest was monitored once in the dataset. In 2012, Nest 13
had four successfully fledged Barn Owl chicks.
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