Lessons Learned from Managing Urban Peregrine Falcon Nests in Kentucky 1997–2021
Michael D. Patton1*, Kate G. Slankard1, and Kasia R. Bradley1
1Kentucky Department of Fish and Wildlife Resources, Sportsman’s Lane, Frankfort, KY 40601 *Corresponding author.
Urban Naturalist, No. 69 (2023)
Abstract
The Kentucky Department of Fish and Wildlife Resources monitored Kentucky’s nesting population of Peregrine Falcons 1997–2021. As part of these efforts, we monitored the productivity and survival of Peregrine Falcons hatched at urban nest sites using alphanumeric, colored leg bands, and used this data to identify which factors contributed most to the recruitment of young into the breeding population. Of the banded, wild-produced birds, 8% were re-sighted as breeders in the Eastern U.S.A and Canada. Parentage was important, and specifically, a few individual falcons produced more offspring that would go on to be breeders, than others. The percentage of falcons produced that became breeders did not differ significantly between natal sites on bridges and other urban locations. Breeding birds at recently discovered cliff nests included two adults that had been wild-produced at urban sites, indicating that continued management of urban sites may aid gradual expansion of the cliff-nesting peregrine population.
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2023 Urban Naturalist 69:1–11
Lessons Learned from Managing Urban Peregrine Falcon
Nests in Kentucky 1997–2021
Michael D. Patton1*, Kate G. Slankard1, and Kasia R. Bradley1
Abstract– The Kentucky Department of Fish and Wildlife Resources monitored Kentucky’s nesting
population of Peregrine Falcons 1997–2021. As part of these efforts, we monitored the productivity
and survival of Peregrine Falcons hatched at urban nest sites using alphanumeric, colored leg bands,
and used this data to identify which factors contributed most to the recruitment of young into the
breeding population. Of the banded, wild-produced birds, 8% were re-sighted as breeders in the Eastern
U.S.A and Canada. Parentage was important, and specifically, a few individual falcons produced
more offspring that would go on to be breeders, than others. The percentage of falcons produced that
became breeders did not differ significantly between natal sites on bridges and other urban locations.
Breeding birds at recently discovered cliff nests included two adults that had been wild-produced at
urban sites, indicating that continued management of urban sites may aid gradual expansion of the
cliff-nesting peregrine population.
Introduction
The Falco peregrinus anatum Bonaparte (American Peregrine Falcon) experienced severe
population decline during the mid-1900s. This decline was mostly attributable to eggshell
thinning caused by the widespread use of the pesticide DDT. By the 1970s, populations east of
the Mississippi River were extirpated (USFWS 2003). Restoration efforts in the 1970s–1990s,
including the release of captive-bred birds into the wild and the outlawing of DDT in the US,
led to a rebound in the nesting population which gained momentum in the Midwestern US
in the 1990s (Redig et al. 2020). In Kentucky, the first nest in decades was established and
documented on a bridge in downtown Louisville during 1997 (Burford 2001).
The American Peregrine Falcon was removed from the United States Fish and Wildlife
Service endangered species list in 1999 (USFWS 1999). Nonetheless, due to local conservation
concern, the Kentucky Department of Fish and Wildlife Resources (KDFWR) listed the
Peregrine Falcon as a Species of Greatest Conservation Need in Kentucky’s State Wildlife
Action Plan (KDFWR 2013), and statewide restoration, management, and monitoring initiatives
for the species continued to ensure Peregrine Falcons maintained healthy population
levels in hopes that the species would re-colonize natural habitats.
Reintroduction efforts in Kentucky occurred from 1993–2003, and 115 captive-bred
birds were released during this timeframe into urban areas and rural habitats near to cliffs
(Dzialak et al. 2005). The KDFWR monitored the nesting population annually starting in
1997 and initiated a nestling banding program in 2001 (Burford 2001). Since then, Kentucky’s
nesting population has steadily increased, totaling 17 territorial pairs documented
in 2021, with 14 nests on manmade structures (Patton and Bradley 2021). With 82% of
Kentucky’s nesting Peregrine Falcon population occurring on manmade structures, it is
important to understand how to effectively manage these sites and determine if these nest
sites contribute to the recolonization of nests at natural cliff sites.
1 Kentucky Department of Fish and Wildlife Resources, Sportsman’s Lane, Frankfort, KY 40601* Corresponding
author – michael.patton@ky.gov
Associate Editor: David Krauss, City University of New York.
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Several studies have investigated the nest success and/or productivity of urban peregrine
nest sites in eastern North America (Gahbauer et al. 2015a, Kelly et al. 2018, Watts et al.
2018) and elsewhere (Altwegg et al. 2014, Kettel et al. 2019). Some of these studies demonstrated
the benefit of nest boxes (Altwegg et al. 2014, Gahbauer et al. 2015a) and rescue
of grounded fledglings (Gahbauer et al. 2015a) for increasing productivity and/or survival.
Dispersal patterns in Peregrine Falcons produced in nest sites in the Eastern US have also
been examined by several studies (Dennhardt and Wakamiya 2013, Faccio et al. 2013, and
Katzner et al. 2012) with females typically dispersing farther than males to their first breeding
location. The effect of natal site type on breeding site selection has also been a topic of
study. Katzner et al. (2012) observed no preference for birds produced at one site type (e.g.,
bridge, building, cliff) to choose to breed at that or another site type. In contrast, Faccio et
al. (2013) found that birds showed a tendency to nest on surfaces that were similar to those
from which they fledged.
Past studies on Peregrine Falcons in Kentucky have focused on reintroduction efforts,
home range, or mitigation techniques (Dzialak et al. 2007, Slankard et al. 2020, Taylor et
al. 2020). Survival of captive-bred falcons during the post-fledging period in 1993–2003
in Kentucky was reported by Dzialak et al. (2007). Mitigation techniques for a pair of
Peregrine Falcons nesting on a bridge during reconstruction were described in Slankard et
al. (2020). While Dzialak et al. (2005) discussed the re-sighting of selected captive-bred
individuals at nest sites, the overall recruitment of birds hacked during 1993–2003 into the
nesting population has not been previously quantified in Kentuck y.
Further, research on the long-term survival and recruitment of wild-produced young
falcons into the breeding population, in relation to natal nest site management, is sparse.
Tordoff et al. (2000) explored the relationship between the size of a brood from which individuals
fledged to their probability of becoming a breeder in the Midwestern US and found
no relation. Gahbauer et al. (2015b) found that wild-produced young were recruited to the
breeding population almost twice as frequently as captive-bred birds in Ontario, Canada.
Since urban nest sites inevitably require management, it is important to managers that these
efforts contribute to the growth and stability of nesting populations.
In this study, we monitored the productivity and survival of Peregrine Falcons hatched
at urban nest sites through the use of alphanumeric, colored leg bands. The objective of this
study was to utilize Peregrine Falcon monitoring data, collected over 25 years in Kentucky,
to guide the management of this species going forward. Specifically, we aimed to identify
factors which contributed most to the recruitment of young into the breeding population.
We further endeavored to evaluate the effects of other management considerations (e.g.,
disease, fledgling rescues, etc.) on the survival and recruitmen t of young falcons.
Methods
Field methods
In order to monitor as much of the Kentucky population as possible, we followed up on
reports from the public to document new nest sites and conducted surveys for nesting at
bridges in 2012 and 2018. We also conducted cliff surveys in areas with suitable cliff habitat
(the Kentucky River Palisades, the Red River Gorge, and various locations in southeast KY)
during 2008, 2011, 2012, and 2018.
To increase nest site availability and productivity, we installed 29 nest boxes at many urban
locations throughout Kentucky between 1997 and 2021. Five nest boxes were installed
on bridges, 5 at industrial facilities, 8 on buildings, and 11 at power plants. At accessible
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sites, we banded nestling Peregrine Falcons between the age of 21 and 28 days. We determined
the sex of individuals using morphological measurements (Cade et al. 1996). Each
Peregrine Falcon was fitted with a United States Geological Survey (USGS) leg band etched
with a unique 9-digit number and a bi-colored band with a unique series of colors, letters,
and numbers. All banding was permitted by the USGS Bird Banding Laboratory (BBL;
Permit #23400). During the years 2005–2021, we tested 238 nestlings for Trichomonas
gallinae Rivolta by use of a mouth swab, which we sent to the University of Tennessee at
Knoxville for culture and/or PCR testing.
We re-sighted the leg bands of individuals through extended observations using a high-powered
spotting scope, observer photography or automated photography (i.e., trail cameras at nest
boxes). We monitored most nest sites during fledging and assisted grounded fledglings, when
found or reported, by placing them back in the nest or at a nearby high location (e.g., rooftop).
Data assembly and statistical analysis
In order to gather data for this study, we queried the BBL for all band encounters of Peregrine
Falcons banded in Kentucky (1997–2021). We also queried the Midwest Peregrine
Society database (Midwest Peregrine Society 2022) for encounter and breeding location
information, in addition to utilizing our own long-term database. One site along the Ohio-
Kentucky state line at the Russell-Ironton Bridge was managed and banded by KDFWR
until 2008 and then the Ohio Division of Wildlife took over management for the site after
the nest moved to the Ohio side of the state line. We include data from this site prior to 2008
and exclude it from that point forward.
Birds were considered breeders if they were observed at breeding age at a nest where eggs,
incubation or chicks were observed. Generalized linear mixed modeling was used to test the
relationship between an individual being re-sighted as a breeder (binary response: breeder or
not breeder) and explanatory variables of natal site type, mother, father, being rescued as a
hatch year, and testing positive for Trichomonas. Akaike Information Criterion (AICc) model
selection was used to select the best fitting model explaining the factors that led to a Peregrine
Falcon becoming a breeder. Model averaging was used to obtain parameter estimates and
95% confidence intervals for multiple competing models (ΔAICc< 2.0) using package MuMIn
and function model.avg (Bartoń 2023). Peregrine Falcons that were captive-bred, banded as
adults, or had unknown natal sites were removed from this portion of the analysis.
We calculated the number of years each breeding adult nested by counting the years
including and between the first year the bird was re-sighted as a breeder and the last year.
We categorized each nest site into 4 types: power plant, bridge, industrial facility, and city
building. Due to a relatively small number of banded, breeding falcons, a Mann-Whitney
U or Kruskal Wallis (when data was non-parametric) test was used to perform univariate
analyses of each attribute to the mentioned responses. We used chi-square goodness-of-fit
tests to compare the association between natal site type and eventual breeding site type, and
between Trichomonas status and being re-sighted as a breeder. The program, R, was used to
perform all statistical analyses (R Core Team 2022).
Results
One hundred fifteen captive-bred Peregrine Falcons were released in Kentucky during
reintroduction efforts (1993–2003). Of these, 3.47% (4/115) became breeders in Kentucky
and 1.7% (2/115) nested outside of the state. The last known, captive-bred breeding adult
from Kentucky died in 2014 at the age of 17 after nesting at a bridge for many years.
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During 1997–2021 there was a growing number of territories and active nests monitored
throughout the state. In 2006 there were 9 territories with six nests, in 2014 there were
13 territories with 10 nests, and in 2021 there were 17 territories with 15 nests. During
1997–2021, 522 known Peregrine Falcon young were wild-produced in Kentucky nests and
67% (348/522) were banded. Of the banded birds, 17% (62/348) were encountered again by
Dec 2021 and 8.0% (28/348) were re-sighted as breeders in the Eastern U.S.A and Canada.
Six percent (21/348; 10 male and 11 female) were confirmed as breeders in Kentucky. Of
all re-sighted falcons, 39% (24/62) were male and 61% (38/62) were female. Of the birds
re-sighted as breeders, 57% (16/28) were male and 43% (12/28) were female.
There were 4 competing models to describe the relationship between banded falcons resighted
as breeders, and the explanatory parameters (Table 1). Through model averaging, parentage,
specifically the male falcon, 816-66344 (P=<0.001) and the natal site type, “industrial
plants” (P=0.032), were found to be the significant coefficients of the competing models.
The male falcon, 816-66344, produced significantly more offspring that would go on to
be breeders than any other male (N=10, P=<0.001; Fig. 1.) The female falcon, 1807-53995,
produced significantly more breeding falcons than any other female (N=6, P=0.002; Fig. 2.).
Statistically, the natal site type and eventual breeding site type were not significantly
associated (P=0.137). The number of offspring produced by a breeding falcon was not
associated with the breeding site type (P=0.888) or the natal site type (P=0.454). Specific
nest sites did vary in the number of breeding birds that were produced and LG&E
Trimble County produced more breeding Peregrine Falcons than other successful nest
sites (Fig. 3). However, the percentage of falcons produced that became breeders did not
differ between natal sites on bridges (pooled) and other urban locations (power plants,
Figure 1. Number of banded offspring per banded, breeding male. Numbers over each bar represent
the number of years an individual nested. Banded offspring were more likely to become breeders if
they were sired by 816-66344.
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skyscrapers, industrial sites, pooled; P=0.08). The amount of banded, breeding falcons in
Kentucky peaked in 2015 and steadily decreased after that, as the population of breeding
birds in the state continued to rise (Fig. 4).
Of the 348 Peregrine Falcons that were banded, 64 (18.4%) were rescued shortly after
fledging. Four of 28 (14.3%) falcons re-sighted as breeders were rescued as fledglings. Being
rescued in the first year after hatching did not increase the likelihood of a falcon being
re-sighted as a breeder (P=0.747), and there was no association with being rescued in the
first year after hatching and the number of offspring produced (P=0.64). The number of
years an adult bird nested was not associated with being rescued as a fledgling (P=0.947).
Of the Trichomonas samples taken (N=238), 19 Peregrine Falcons tested positive. None of
the 19 falcons that tested positive for Trichomonas were re-sighted as adults and there was
no statistical association between the two variables (P=0.27).
Figure 2. Number of banded offspring per banded, breeding female. Numbers over each bar represent
the number of years each individual nested. The female falcon, 1807-53995, produced significantly
more breeding offspring than any other banded female falcon.
Table 1. The 4 best fit models that describe which factors influence a Peregrine Falcon to become a
breeding bird.
Models AICc AiCcWt Cum. Wt LL
Father + Trichomonas 0 0.25 0.25 -78.30
Natal Site + Trichomonas +
Father
0.58 0.19 0.44 -75.21
Father 0.61 0.18 0.62 -80.83
Natal Site + Trichomonas 1.92 0.10 0.72 -91.14
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Discussion
A significant goal in restoration efforts was to reestablish the species in historic cliff
nesting habitats, and 2 nest sites on natural cliffs have been discovered in Kentucky in
recent years. Breeding birds at these sites included un-banded birds, as well as a female
that had been wild-produced at a bridge, and a male that was wild-produced at a power
plant. Unfortunately, these cliffs are not accessible for nestling banding, but the presence
of nesting adults which originated from human-made natal sites is encouraging that continued
management of urban sites may lead to further expansion of the peregrine population
to more cliff sites, albeit slowly.
Rangewide, the goal of returning this species to cliff habitats has been met with mixed
success thus far (Watts et al. 2018). Use of human-made structures for nesting has become
fairly widespread in urban areas, whereas the species only occasionally used these areas in
North America prior to reintroduction (Faccio et al. 2013). The positive side to this result
may be population resiliency to climate change. Sumasgutner et al. (2020), studied the
breeding performance of Peregrine Falcons under varying weather conditions and found
that falcons breeding in nest boxes were less sensitive to local weather changes than pairs
using natural nest sites. Based on these results, they suggested that the urban peregrine
population may better withstand climate change and extreme weather events.
Bridge sites can require considerable mitigation and coordination when it comes to
bridge maintenance (Slankard et al. 2020). Thus, the contribution of these sites to the
greater population is worth evaluation. We found no significant difference between bridge
sites (pooled) and other site types (pooled) in the production of young that eventually became
breeders (Fig. 4). Other studies have noted lower productivity at bridge sites when
comparing to other urban site types (Gahbauer et al. 2015a), and fledging success can be low
at bridge sites (Bell et al. 1996). However, our data shows these sites can produce young
which contribute to the nesting population. A reduced number of young may benefit the
fitness of those surviving to dispersal age at bridge sites due to increased parental care during
the post-fledging window. We also installed nest boxes at selected bridges and rescued
several young from bridge sites. Assistance with fledging may boost survival at these sites
even though we didn’t find that fledging assistance increased the likelihood of a falcon being
re-sighted as a breeder overall. Four of 28 (14.3%) falcons, re-sighted as breeders, were
rescued as hatch years, and two of these were hatched at bridge sites. Thus, assisted fledging
may be worthwhile, in the early phase of a species' recovery or when a significant portion
of the population occurs on bridges.
None of the 19 falcons that tested positive for Trichomonas were re-sighted as adults,
possibly indicating that exposure to this disease during the nestling phase may be catastrophic
for survival. Exposure to trichomonads has been associated with consumption
of pigeons and doves (Columbiformes) as prey, but may also be found in some passerines
(Anderson et al. 2010, Samour and Naldo 2003). Urban peregrines are more likely to rely
on pigeons for a large portion of their diet, and thus, this threat is probably more significant
for urban nests.
Statistically, the natal site type and eventual breeding site type were not significantly
associated in our study. Our results agreed with the findings of Katzner et al. (2012), which
observed no preference for birds produced at one site type (e.g., bridge, building, cliff) to
choose to breed at that or another site type. However, our results conflicted with Faccio et
al. (2013), which found that birds showed a tendency to nest on surfaces that were similar
(cliff vs. building) to those from which they fledged.
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Due to accessibility and safety issues, we focused our banding efforts at sites where
nests were in nest boxes. However, all sites were monitored for banded breeding adults,
regardless of nest box status. Therefore, it’s important to consider that our sample of banded
birds from sites where the nest was not in a nest box was extremely small. In addition, while
the natal site type, “industrial plants”, was found to be important for falcons re-sighted as
breeders, we think this was an effect of a small sample size of birds banded at this site type.
We did not find that the number of recruited offspring produced by a breeding falcon
was associated with the breeding site type. However, we did observe differences between
nesting sites and the number of breeding birds that were produced, with one site producing
more than the others. This is further discussed below, but we surmise that local-scale site
specifics (structure, predator abundance, etc.) are likely more important for survivability
than the generalized type of the site (power plant vs. city building).
We found parentage to be important for future recruitment. It has been inferred in the
past that individuals vary in productivity, which is correlated with life span (Tordoff and
Redig 1997). In theory, longer lived birds should produce more offspring that are recruited
into the nesting population. In addition, Peregrine Falcons that start breeding in their first
year have been found to have greater lifetime reproductive success than birds entering the
breeding pool as adults (Zabala and Zuberogoitia 2015). Vergara et al. (2010) found that
Figure 3. Young produced (wild) and banded at nest sites where young were banded. LG&E Trimble
Co. Station produced more young later re-sighted as a breeder than any other site.
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fledglings raised by higher-quality (as assessed using body condition and mass), Eurasian
Kestrel (Falco tinnunculus) parents showed longer post-fledging dependence periods, a crucial
stage for survival. The male (816-66344) that produced the most offspring which later
became breeders (Fig. 1) was a captive-bred individual. His success was supported by an
8-year term of nesting at the same site and a long lifespan (14 years). However, many breeding
males had longer nesting terms and did not produce as many young that were recruited
into the nesting population (Fig. 1). The female falcon (1807-53995) that produced the most
offspring, which later became breeders (Fig. 2), was a wild-produced individual that was the
mate of (816-66344) for 7 years. Again, many breeding females had longer nesting terms
and did not produce as many young that were recruited into the nesting population (Fig.
2). The nuances of this pair’s particular nest site which did produce more recruited young
than other sites were likely important, in addition to behavioral parental factors and a long
nesting term for the pair (not just each individual). Although we did not find an association
between the number of offspring produced by a breeding falcon and the breeding site type
(power plant, bridge, etc.), it is apparent that some nest sites are superior, due to structural
characteristics, than others. For instance, this pair’s nest site was in a nest box in the side of
a building at a power plant that had a lower rooftop directly in front of it. The simple availability
of a safe location, off the ground, for fledging to occur may make this site superior for
long term survivability. Further study would help to discern the importance of site-sp ecific
vs. parental factors in the production of recruited young.
Figure 4. The number of breeding and banded, and total breeding Peregrine Falcons in Kentucky with
mean age by sex during 2000–2021.
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Our long-term monitoring efforts documented some fairly lengthy nesting terms for both
male and female breeding falcons, with a few individuals of each sex nesting for over a
decade (Figs. 1 and 2). Our anecdotal observations, satellite tracking and long-term monitoring
efforts suggest Kentucky’s nesting Peregrine Falcon population is non-migratory,
residing at territories year-round (Taylor et al. 2020), and this may support longevity at
nesting territories. Remaining at territories year-round circumvents migration, which is
energetically expensive and can lead to greater mortality (Newton 2007; Franke et al. 2011).
Most of the expansion of the nesting population in recent years has been supported by
nest box installations and partnerships with relevant utility companies, industrial facilities,
and public agencies (i.e., transportation). In 2021, 63% (10/16) of Peregrine Falcon nests in
Kentucky were in nest boxes and 59.4% (19/32) of young known to fledge came from these
nests (Patton and Bradley 2021). The dependence of the population on partnerships and nest
boxes will no doubt require management effort into the future to sustain the population and
spur further growth into cliff habitats. Evaluations of monitoring data such as this can be useful
for prioritizing these efforts going forward. When management resources are limited, it is
reasonable to focus efforts on the sites which lead to the most eventual recruitment (Fig. 3).
As evaluations like these are not possible without banding efforts, some level of banding
is required to make such assessments into the future, if desired. During 1997–2021,
67% (348/522) of known Peregrine Falcon young, wild-produced in Kentucky, were
banded and 50.0% (21/42) of the banded falcons that nested in Kentucky were wildproduced
here. Thus, band recovery ratios are no doubt affected by the amount of banding
effort conducted elsewhere in the region. The number of banded, breeding birds in
Kentucky peaked in 2014 and 2017 and steadily decreased after that (See Fig. 4), despite
the number of nesting pairs continuing to increase. Federally coordinated post-delisting
monitoring efforts ended in 2015, and banding efforts in some states ceased or were cut
back at that point (Midwest Peregrine Society 2022). Thus, this pattern likely reflects a
falling percentage of banded birds in the regional population.
The mean age of banded, breeding falcons has increased, especially over the past decade,
indicating the banded, breeding population is aging (See Fig. 4). While this probably
represents good longevity in breeding individuals, we may see a continued decline in the
number of banded, breeding individuals in the coming years as these older birds are replaced
and a smaller proportion of the nestlings are banded. While regional banding efforts
are likely to continue to decrease going forward, the banding studies for Peregrine Falcons
across the Eastern US during this species’ recovery have demonstrated the dispersal and
movement capabilities of these birds across state lines. Overall, these efforts emphasize the
need to manage this population at the regional level to maintain long term stability.
Acknowledgments
We recognize the many cooperators that support Peregrine Falcon nest sites, and acknowledge Louisville
Gas and Electric Company and Kentucky Utilities Company for funding. We thank our nongame
bird technicians and previous biologists for their time on this project: Laura Burford, Shawchyi
Vorisek, Loren Taylor, Budd Veverka, Adam Smith, Megan Connor, Dan Stoelb, Ben Leffew, Tonya
Mammone, Caleb Switzer, Michael Arnold, Rashelle Juric, Bree Furfey, Meghan Raley, and Benjamin
Bowman. We acknowledge Dr. Rick Gerhold at the University of Tennessee, Knoxville, for disease
testing. We also worked with the following rehabilitators on falcon rescues: Raptor Rehabilitation
of Kentucky, Wingspan of Kentucky, and Broadbent Wildlife Sanctuary. We thank the Midwest Peregrine
Society for coordinating monitoring and data organization through the years.
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