Introduction
Anthropogenic effects on wildlife are ubiquitous and increasing (Dirzo
et al. 2014; Venter et al. 2016; Ibisch et al. 2016; Ceballos et al.
2017). Carnivores are particularly susceptible to human disturbance, due
to their large home range requirements and sensitivity to habitat
fragmentation (Palomares and Caro 1999; Crooks 2002). In recent history
many carnivore ranges have been reduced and/or fragmented due to
colonization and human expansion (Crooks 2002). The bobcat (Lynx
rufus ) is among these carnivores; native to North America, bobcats are
a medium-sized felid that occur from southern Canada to central Mexico,
and historically spanned all 48 contiguous U.S. states (Reding et al.
2012). However, in the mid 1800’s bobcats were extirpated from a number
of states along the Northeast and the Midwest, including Ohio, due to
deforestation and overharvesting (Reding et al. 2012). In recent years,
bobcat populations have begun to recover in many of these states (Deems
and Pursley 1978). In 1946 an adult male killed along the Ohio River in
Scioto was the first record of a bobcat in Ohio after a century of
extirpation (ODNR 2018), and the number of confirmed bobcat sightings
has been steadily increasing since (Bobcat Management Plan 2023). Recent
evidence indicates that bobcats have successfully recolonized Ohio and
are expanding their range (Roberts and Crimmins 2010; ODNR 2018; Prange
and Rose 2020; Popescu et al. 2021), prompting the Ohio Department of
Natural Resources (ODNR) to remove them from the Ohio Endangered and
Threatened Species List. Consequently, there is increased interest from
recreational hunters and trappers to open a harvest season for bobcats
in Ohio. Bobcats are classified as a furbearing animal in Ohio under
Ohio Revised Code Section 1531.01 and Ohio Administrative Code Rule
1501:31-1-02, while harvest is not currently permitted in Ohio, legal
harvest of bobcats occurs in 39 of the 47 states within their current
range. However, important population factors such as abundance and
density of the Ohio populations are currently unknown and bobcat density
varies widely across their range (Ferguson et al. 2009). Therefore,
research is needed to investigate density and abundance of bobcats in
the state to inform current and future management.
Genetic research conducted on bobcat samples from the early 2000s
indicated that bobcat recolonization in Ohio occurred sequentially with
two genetically distinct subpopulations in southern and eastern Ohio
(Anderson et al. 2015). The eastern population was founded from
individuals in West Virginia and was thought to be self-sustaining by
2012, whereas the southern population was dependent on continual
immigration from founder animals in Kentucky (Anderson et al. 2015).
Researchers also found differences in the average home-range size for
bobcats between these areas; bobcats in the southern Ohio area had
significantly larger home ranges and core areas then those in the
eastern area (Prange and Rose 2020). These regional differences in space
use could be a result of differences in habitat quality and degree of
population recovery, which would ultimately affect the density of
bobcats in the two areas. This has implications for management of the
bobcat population in Ohio, particularly if lethal harvest is to be
considered in this recovering population. For example, as part of
ongoing efforts to understand the long-term viability of bobcats in
Ohio, we determined that density was a critical parameter in predicting
future population trajectories via spatial population simulation models
(Dyck et al. In review). Thus, the applicability of these models to
inform management decisions is contingent on accurate bobcat density
estimates for different regions of Ohio. Although recent research shows
evidence of genetic admixture between the southern and eastern
populations (Heffern 2021), other sources of data (citizen sightings,
roadkill, camera trap) suggest that regional differences in density and
abundance likely still persist. Therefore, we predict that bobcat
density will be lower in southern Ohio compared to eastern Ohio.
Harvest data are used in many states to track population trends of
bobcats and inform management decisions (Roberts and Crimmins 2010).
However, given that these data are not available for Ohio’s population,
we used non-invasive sampling to estimate density for bobcats in
southeast Ohio. Non-invasive sampling is a particularly useful tool for
monitoring cryptic and wide-ranging species such as carnivores (Kelly et
al. 2012; Davidson et al. 2014). We used DNA from scat as opposed to
motion-triggered cameras (another common non-invasive method used with
capture-recapture models to estimate animal density; Karanth and Nichols
1998; Royle et al. 2009) for our study because of the tendency for
bobcats in this region to have indistinct markings, thus leading to
unreliable individual animal identification (Morin et al. 2018). Studies
have found that non-invasive genetic surveys are an efficient
alternative to camera trap surveys for estimating abundance and density
of bobcats and other carnivores (Waits et al. 2001; Waits and Paetkau
2005; Ruell et al. 2009; Morin et al. 2018).
In this study, we implemented a multi-occasion scat sampling protocol at
three public land areas in southeast Ohio (1 in eastern and 2 in
southern Ohio) to estimate regional population abundance and density of
the returning bobcat population. We used capture histories generated
from the scat samples with spatially explicit capture-recapture (SECR)
analysis for density estimation (Efford 2022). The SECR framework
utilizes the spatial data associated with detectors to account for
animal movement and generate robust density estimates by avoiding biases
in calculating the effective sampling area (Efford 2004; Borchers and
Efford 2008; Royle and Young 2008).