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).