Woodrats (Neotoma spp.) are imperiled in the north-central and north eastern United States. In Illinois, eastern woodrats (N. floridana) experienced range reductions and population bottlenecks over the past century. Hypothesized reasons for the decline of many woodrat populations that inhabit rock outcrops in the eastern United States include parasitism by raccoon roundworms (Baylisascaris procyonis), hard mast shortages, owl predation, and reductions in crevice availability for nest construction. During 2004-2005, the isolated remnant populations along the Mississippi bluffs in southwestern Illinois were genetically augmented with 47 eastern woodrats from Arkansas and Missouri resulting in 40% admixture within the largest population. In 2009, a strong windstorm created canopy gaps and woody debris throughout this area, potentially improving habitat for eastern woodrats. During 2003–2009, 422 eastern woodrats were reintroduced to 5 sites in the southeastern Illinois, and 172 eastern woodrats to 2 southern Illinois state parks during 2013–2014. These reintroductions are the only woodrat reintroductions to date with >50 individuals released per site. Most previous woodrat reintroduction attempts have released small numbers of individuals (10–15 per site and 10–54 total) and either failed to establish populations or required frequent management for populations to persist. My objectives were to (1) investigate the status of augmented eastern woodrat populations in southwestern Illinois, (2) evaluate the success of the southern Illinois reintroductions, (3) investigate whether eastern woodrats demographics within a reintroduced metapopulation could be predicted by factors underlying hypothesized reasons for woodrat declines, and (4) develop and evaluate noninvasive alternatives to live-trapping and sign surveys for monitoring woodrat populations.
To address my first objective (Chapter 2), I live-trapped remnant eastern woodrat populations in southwestern Illinois and conducted sign surveys during 2011-2015. I captured 263 eastern woodrats with mean trapping success 62.5% higher than trapping during the 1990s and number of individuals captured per trap-night 3-6 times higher than trapping events during the previous 18 years (all P <0.001). I also located eastern woodrat sign 8.9 km east of the remnant populations. I recommended further genetic monitoring to evaluate if population increases are coupled with increased admixture. I also recommend forest management actions that result in periodic habitat disturbance and piles of woody debris to increase eastern woodrat habitat quality.
To address my second objective (Chapter 3), I compared eastern woodrat abundance and distribution to published performance indicators. During 2012–2014, I captured 436 individual eastern woodrats from the southeastern Illinois and located eastern woodrats nearly 9 km from release sites. In 2017, I captured 52 eastern woodrats at the state parks. My findings indicated that these eastern woodrat reintroductions could be considered successful and potentially successful. My results added to the sparse information on successful rodent reintroductions. Managers can use this information to inform structured decision making for future conservation and management actions.
To address my third objective (Chapter 4), I tested whether abundance and apparent survival of eastern woodrats within the reintroduced metapopulation in southern Illinois could be predicted by availability of hard-mast-producing trees, great horned (Bubo virginianus) and barred (Strix varia) owl abundance, prevalence of raccoon roundworm infected northern raccoon latrines, and crevice availability. To do so, I analyzed capture histories of 205 eastern woodrats in summer 2013 and 2014 from 8 rock outcrop sites to estimate local population size and apparent survival. Mean monthly estimated eastern woodrat abundance at sites ranged from 0.78 to 21.58 in 2013 and 0.48 to 18.08 in 2014, while monthly apparent survival ranged from 0.00 to 0.76 during the summers and 0.05 to 0.90 during the trapping intersession. Crevice availability (P = 0.019) and owl abundance (P = 0.019) both were positively associated with eastern woodrat abundance, and crevice availability (P = 0.023) was also positively associated with apparent survival of eastern woodrats. I concluded that crevice availability was the best predictor of eastern woodrat population success, while owl abundance may be a proxy for other habitat variables or a response to eastern woodrat abundance. Nesting structure is likely the primary limiting factor for eastern woodrat abundance in Illinois when populations are not limited by food, raccoon roundworm, or excessive predation. Creating additional nesting structure along outcrops, through forestry practices or the creation of artificial nesting structures, could be useful for increasing woodrat abundance. I suggested a larger-scale multi-state study to identify common habitat factors that are predictive of local woodrat survival and abundance. This would add greatly to the understanding of woodrat populations and aid both management of imperiled populations and future reintroductions.
To address my fourth objective (Chapter 5), I deployed baited camera traps and baited track plates to monitor eastern woodrat presence along rocky outcrops at 4 of the eastern woodrat reintroduction sites in southeastern Illinois, during May 2013 (5 camera and track-plate stations/site) and May and September 2014 (4 camera and track-plate stations/site) to compare their effectiveness. During each deployment, camera traps detected eastern woodrat presence at all 4 sites while track plates only detected presence at 2–3 sites. A greater proportion of camera traps than track plates recorded detections during each deployment. Camera traps required more person-hours to deploy and retrieve, but resulted in more detections per hour effort than track plates. I concluded that baited camera traps are superior to baited track plates for detecting and monitoring woodrat presence.