Trees, owls, worms, and crevices: which habitat factors predict local woodrat demographics?

Abstract

Hypothesized reasons for the decline of many woodrat populations in the eastern United States include parasitism by raccoon roundworm (Baylisascaris procyonis; Ascaridida: Ascarididae), hard mast shortages, owl predation, and reductions in suitable structures (e.g., rock crevices) for nest construction. We investigated whether abundance and apparent survival of eastern woodrats (Neotoma floridana) within a successfully reintroduced metapopulation in southern Illinois could be predicted by factors underlying these hypothesized reasons for woodrat declines. We analyzed capture histories of 205 eastern woodrats from eight rock outcrop sites in summers of 2013 and 2014 to estimate local population size and apparent survival. We then used repeated-measures models to test how woodrat abundance and apparent survival were associated with availability of mast trees, owl abundance, risk of raccoon roundworm infection, and crevice availability. Mean monthly estimated 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 was positively associated both with abundance and apparent survival of woodrats. Our results did not support the hypothesis that owls reduce woodrat populations because woodrat abundance was positively associated with owl abundance across sites. No raccoon roundworm eggs were found at any site. We conclude that crevice availability was the best predictor of woodrat population success in our study area, while owl abundance may be a proxy for other habitat variables or a response to woodrat abundance. Our findings suggest measures that could be taken to benefit woodrat survival and abundance.