Survival and Cause-Specific Mortality of Coyotes on a Large
Military Installation
Elizabeth R. Stevenson, M. Colter Chitwood, Marcus A. Lashley, Kenneth H. Pollock, Morgan B. Swingen, Christopher E. Moorman, and Christopher S. DePerno
Southeastern Naturalist, Volume 15, Issue 3 (2016): 459–466
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E.R. Stevenson, et al.
22001166 SOUTHEASTERN NATURALIST 1V5o(3l.) :1455,9 N–4o6. 63
Survival and Cause-Specific Mortality of Coyotes on a Large
Military Installation
Elizabeth R. Stevenson1,*, M. Colter Chitwood1,2, Marcus A. Lashley1,3,
Kenneth H. Pollock1, Morgan B. Swingen1, Christopher E. Moorman1, and
Christopher S. DePerno1
Abstract - Canis latrans (Coyote) recently expanded into the southeastern United States,
creating ecologically novel interactions with other species. However, relatively few studies
have examined vital rates of southeastern Coyotes or estimated vital rates where individuals
are protected from hunting and trapping. In 2011, we captured and attached GPS radiocollars
to 31 Coyotes at Fort Bragg Military Installation, NC, where Coyote harvest was
restricted. We used a 12-month period (February 2011–January 2012) and known-fate modeling
in Program MARK to estimate annual survival. Model-selection results indicated the
time-varying model (S[t]) was the most parsimonious model, and. annual survival was 0.80
(95% CI = 0.60–0.91). We documented 7 mortalities, including 2 from vehicles, 2 from offsite
trapping, and 3 from unknown causes. Estimated Coyote survival rates at Fort Bragg
were similar to most other estimates from the southeastern US. Anthropogenic causes of
mortality were important even though hunting and trapping were restricted locally.
Introduction
Prior to the 1940s, Canis latrans Say (Coyote) was restricted to western North
America (Nowak 1978). However, Coyotes now occur throughout the eastern United
States (Parker 1995), including the most recent expansion into the southeastern
United States (Hill et al. 1987). For example, Lovell et al. (1998) documented a
7.5-fold increase in Coyote population size since 1980 in Mississippi. Similarly,
Main et al. (2000) reported that Coyote distribution continued to expand southward
in Florida, and the rate of spread increased over the most recent decade. In North
Carolina, Coyotes rarely were reported prior to the early 1980s but were documented
in all counties by 1998 (DeBow et al. 1998). Other states in the southeastern
US have reported similar trends in recent Coyote expansion and population growth
(Houben 2004).
As Coyote populations continue to expand in range and abundance, wildlife
managers have expressed concerns about the ecological impact of Coyotes,
especially related to prey populations. Ample evidence suggests the effects of
Coyotes on community structure may be far reaching (Gompper 2002); effects
may be indirect (e.g., resource competition with species such as Lynx rufus Kerr
1Fisheries, Wildlife, and Conservation Biology Program, North Carolina State University,
Raleigh, NC 27606. 2Department of Fisheries and Wildlife Sciences, University of Missouri,
Columbia, MO 65211.3Department of Wildlife, Fisheries, and Aquaculture, Mississippi
State University, Mississippi State, MS 39762. *Corresponding author - estevenson@
al.umces.edu.
Manuscript Editor: Andrew Edelman
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[Bobcat]; Litvaitis and Harrison 1989) or direct (e.g., predation). For example,
numerous studies in the Southeast have documented direct effects of Coyotes on
Odocoileus virginianus Zimmermann (White-Tailed Deer) (e.g., Chitwood et al.
2015, Kilgo et al. 2012). Though recent focus has been directed toward negative
effects of expanding Coyote populations on prey species and competitors, other
evidence suggests positive implications of Coyote presence. For instance, Brady
(1994) reported eradication of Canis familiaris L. (Feral Dog) following Coyote
establishment in southeastern New York. Similarly, because Coyotes compete
with and depredate Vulpes vulpes L. (Red Fox) and Procyon lotor L. (Raccoon),
Coyote presence has resulted in increased nesting success of Anas. spp. (Duck)
and Melospiza melodia Baird (Song Sparrow) (Rogers and Caro 1998, Sovada et
al. 1995). Also, increases in songbird diversity have been associated with Coyote
predation on Felis catus L. (Feral Cat; Crooks and Soulé 1999). The complex ecological
effects of Coyotes highlight the need for a comprehensive understanding
of Coyote vital rates throughout their new range.
Despite increased interest in the community-level effects of Coyote expansion,
relatively few studies have examined vital rates of Coyotes in the southeastern US.
Because Coyote vital rates vary considerably across their range (Gompper 2002),
estimation of population-specific vital rates is needed to construct accurate Coyote
demographic models and inform management practices in the southeastern US.
Therefore, we quantified survival and determined causes of mortality for a population
of Coyotes at Fort Bragg Military Installation, NC. Specifically, our objectives
were to (1) estimate annual survival, (2) determine potential effects of sex and age
on survival, and (3) determine causes of mortality.
Field-Site Description
Fort Bragg Military Installation (hereafter Fort Bragg) is located in southcentral
North Carolina, in the Sandhills ecoregion. At the time of the study, Fort
Bragg consisted of 73,469 ha and was one of the largest contiguous blocks of
the threatened Pinus palustris Mill (Longleaf Pine) ecosystem in the southeastern
United States. The Pine/Scrub Oak sandhill community described by Sorrie
et al. (2006) was widespread and abundant within Fort Bragg and was dominated
by Longleaf Pine, Quercus laevis Walter (Turkey Oak), and Aristida stricta
Michx (Wiregrass). Upland forests were managed with growing-season prescribed
fire on a 3-year fire-return interval (Lashley et al. 2014). Coyotes were
first documented at Fort Bragg in 1989 and were considered well established by
the mid-1990s (Chitwood et al. 2015). Historically, Fort Bragg allowed Coyote
hunting when other game seasons were open; however, trapping never has been
permitted on the base. According to Fort Bragg estimates, less than 10 Coyotes were removed
each year through hunter harvest (J. Jones, Fort Bragg Wildlife Branch,
Fort Bragg, NC, pers. comm.). During our study period, Fort Bragg suspended
Coyote hunting.
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Methods
Coyote capture and monitoring
We captured Coyotes throughout Fort Bragg using MB-550 foothold traps
(Minnesota Trapline Products Inc., Pennock, MN) from February–May 2011.
We manually restrained trapped Coyotes and recorded sex and weight for each.
We determined age (juvenile [≤1 year], subadult [between 1 and 2 years], adult
[≥2 years]; Gier 1968) based on tooth wear. We fitted each with a Wildcell SG
global positioning system (GPS) radiocollar (Lotek Wireless Inc., Newmarket,
ON, Canada) and programmed radiocollars to obtain relocation data at 3-hour intervals
and to transmit all data to a remote site until a collar was no longer being
monitored due to Coyote mortality, loss of signal, or pre-programmed collar release
(70 weeks following deployment). To determine cause of death, we located
collars that were transmitting a mortality signal and subsequently performed a
field necropsy. We classified mortalities as unknown when field evidence was
not sufficient to identify cause. All Coyote trapping and handling methods were
approved by the North Carolina Wildlife Resources Commission and the North
Carolina State University Institutional Animal Care and Use Committee (Protocol:
11-005-O) (Elfelt 2014).
Data analysis
We used a Kaplan-Meier known-fate model (Kaplan and Meier 1958) in Program
MARK version 8.0 (White and Burnham 1999) following a staggered-entry
procedure (Pollock et al. 1989) to estimate monthly survival for the 21-month study
period. We estimated annual survival for February 2011 through January 2012 by
truncating the 21-month study period.
To determine the importance of sex and age on survival, we used an information
theoretic approach to select from a priori models (Burnham and Anderson 2013).
We first compared time-varying (S[t]) and time-constant (S[.]) survival models. We
then determined the relationship of survival estimates to age and sex covariates by
using the best time-predicted model. We used Akaike’s Information Criterion adjusted
for small sample size (AICc) and compared ΔAICc values and model weights
(wi) to determine the most parsimonious model. We considered models with ΔAICc
values ≤ 2 units from the top model as best-supported models (Burnham and Anderson
2013); however, we used model deviance to omit best-supported models that
contained uninformative parameters (Arnold 2010).
Results
We attached GPS collars to 31 Coyotes, including 19 males (4 juveniles, 3 subadults,
and 12 adults) and 12 females (4 juveniles, 5 subadults, and 3 adults). We
monitored Coyotes from February 2011–October 2012. Three Coyotes (1 subadult
male, 1 subadult female, and 1 juvenile female) dispersed from the study area,
established home ranges elsewhere, and were excluded from analyses. We documented
7 mortalities, including 2 from vehicle collisions, 2 from off-site trapping,
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and 3 from unknown causes (Table 1). Vehicle collisions occurred in March and
April, whereas both trapping mortalities occurred in January.
The best model indicated survival varied monthly (i.e., S[t]; Table 2). The timevarying
models that included age and sex separately received some support (i.e.,
these models fell within 2 ΔAICc of the S[t] model); however, model deviance was
not markedly different from the S(t) model, indicating the addition of age or sex to
the S(t) model was uninformative. Thus, using the S(t) model, monthly survival for
our 21-month study period ranged from 0.86 (January 2012) to 1.00 (most months)
(Fig. 1), and annual survival from February 2011 through January 2012 was 0.80
(95% CI = 0.60–0.91).
Discussion
Annual Coyote survival rates at Fort Bragg were greater than those reported
in Georgia (0.50; Holzman et al. 1992), but other estimates from the southeastern
US were similar (i.e., included within our 95% confidence interval [South Carolina:
0.67 (Schrecengost et al. 2009); Mississippi; 0.73 (Chamberlain and Leopold
2001)]). Known mortality causes within the boundaries of Fort Bragg were limited
to vehicle collisions; however, 2 Coyotes that left Fort Bragg were legally
trapped, highlighting the influence of anthropogenic effects (i.e., hunting, trapping,
vehicles) on Coyote survival. The proportion of Coyote mortalities that are anthropogenic
vary throughout the Southeast and range from 22% in Georgia (Holzman et
al. 1992) to 60% in South Carolina (Schrecengost et al. 2009). We provide evidence
that anthropogenic sources of mortality appear to be important even where Coyote
hunting and trapping are prohibited.
Table 2. Full set of candidate models, including number of parameters (k), Akaike’s Information
Criterion values corrected for small sample size (AICc), ΔAICc, AIC weights (wi), and model deviance
for estimating Coyote monthly survival (n = 28), Fort Bragg Military Installation, NC, February
2011–October 2012.
Model k AICc ΔAICc wi Deviance
S(t) 5 59.4209 0.0000 0.51853 49.2514
S(t + age) 6 61.2196 1.7987 0.21096 48.9816
S(t + sex) 6 61.3897 1.9688 0.19376 49.1517
S(t + age + sex) 7 63.2825 3.8616 0.07520 48.9643
S(.) 1 71.0369 11.6160 0.00156 69.0257
Table 1. Causes of mortality among 28 Coyotes captured at Fort Bragg Military Installation, NC,
February 2011–October 2012.
Trapping Vehicle Unknown
Age at mortality Male Female Male Female Male Female
Juvenile (<1 year) 0 0 0 0 0 0
Subadult (1–2 years) 0 1 0 2 1 0
Adult (>2 years) 1 0 0 0 2 0
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Despite Fort Bragg being protected from hunting and trapping, 2 Coyotes were
trapped during the study period; this result was likely due to wide-ranging movement,
as both trapping events occurred in January on private la nds just outside the
boundary of Fort Bragg. Elfelt (2014) documented large home ranges and high
numbers of transient Coyotes at Fort Bragg, a phenomenon possibly attributed to
high Coyote population density, increased territoriality among older adults, and
low resource availability (Conner et al. 2008, Gese et al. 1996). During our study,
15 Coyotes left the boundaries of Fort Bragg at least once, which predisposed them
to hunting and trapping on adjacent private land. Proportions of Coyote populations
that are transient or dispersers are high (e.g., Chamberlain et al. 2000, Hickman
et al. 2015, Hinton et al. 2012). Therefore, Coyote populations in the southeastern
US may remain vulnerable to hunting and trapping mortality despite localized protected
status because wide-ranging individuals are common and frequently move
into unprotected areas.
Two mortalities during the study period were caused by vehicles. The majority
of roads at Fort Bragg are low-traffic sandy roads that are used for military training
and function as firebreaks for prescribed fire. However, several paved and gravel
roads experience greater amounts of military and civilian vehicle traffic. During our
study, 1 Coyote was killed on a paved high-traffic road, while another was killed on
a relatively low-traffic gravel road. Coyote mortality rates due to vehicle fatalities
vary throughout their range and are dependent on level of urbanization and road
density (Gehrt 2007). No other Coyote survival studies in the southeastern United
States have reported vehicle-related mortalities (Chamberlain and Leopold 2001,
Holzman et al. 1992, Schrecengost et al. 2009), but those studies had small numbers
of Coyote mortalities, low road density, or few paved roads.
Figure 1. Monthly Coyote survival estimates (n = 28) for a 21–month period at Fort Bragg
Military Installation, NC, February 2011–October 2012.
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Our results indicated little support for age and sex effects on Coyote survival,
which is similar to other studies in the region (age: Holzman et al. 1992; sex: Chamberlain
and Leopold 2001, Schrecengost et al. 2009). These studies and ours may
have been limited by small sample sizes that precluded the ability to make inferences
regarding the role of sex and age. Studies from elsewhere in North America
have indicated that age is a significant source of variation in survival, with juveniles
reportedly having lower survival relative to adults (e.g., Parker 1995, Van Deelen
and Gosselink 2006, Windberg 1995). However, sex does not appear to be a significant
source of variation in Coyote survival elsewhere in the United States (e.g.,
Van Deelen and Gosselink 2006, Windberg et al. 1985). Future studies with larger
sample sizes may be better equipped to assess the effects of age and sex on Coyote
survival in the southeastern United States.
This study demonstrates that anthropogenic activities are a primary cause of
mortality for Coyotes, even in areas with low hunting and trapping effort. Transient
individuals likely will be susceptible to anthropogenic mortality sources even on
large public land bases like Fort Bragg, where hunting effort was low. Interestingly,
the survival rate in our study was greater than all other reported estimates in
the region, so local policies that restrict hunting and trapping may confer greater
Coyote survival, potentially yielding an age structure different than surrounding
populations where hunting or trapping efforts are more substantial. This result has
implications on potential management strategies that employ Coyote removal as a
tool to mitigate undesired effects on other taxa (e.g., depredation of White-Tailed
Deer). Future research could explore the population-level effects of anthropogenic
mortality on Coyote age structure in the Southeast and how Coyote age structure
contributes to direct or indirect effects on prey species and community structure.
Acknowledgments
Funding for this project was provided by the United States Department of Defense, the
Fort Bragg Wildlife Branch, and the Fisheries, Wildlife, and Conservation Biology Program
at North Carolina State University. We thank USDA APHIS Wildlife Services, especially
T. Menke and S. Thompson, for assistance with Coyote trapping. We thank A. Schultz, J.
Jones, C. Brown, J. Heisinger, and the Fort Bragg Wildlife Branch for logistical support.
We thank E. Kilburg, M. Nunnery, A. Prince, A. Schaich Borg, B. Sherrill, and many other
volunteers for assistance in the field. We thank R. Meentemeyer, A. Edelman, and 2 anonymous
reviewers for providing constructive comments that improved the manuscript.
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