Effects of demography and urbanization on stress and body condition in urban white-tailed deer

Abstract

White-tailed deer (Odocoileus virginianus) are becoming increasingly common in urban environments. How they respond to potential changes (i.e. increased human interactions, traffic, overabundance) can influence herd health. We aimed to develop a technique that quantifies stress in deer using hair cortisol concentrations (HCC). Our objectives were to test for: 1) a relationship between HCC and deer body condition score (BCS); 2) effects of sex, age, and location on HCC; and 3) effects of herd density and urbanization on HCC. Using the HCC of 59 culled deer from 8 sites (Cook County, IL USA), of which 7 sites were part of yearly herd management to maintain population sizes (site was managed) and 1 site was not (un-managed), we found deer with the poorest BCS had the highest HCC (P < 0.01). We then compared HCC from 342 deer, from 24 managed sites in 4 counties (IL, USA), to test for the effects of biological and environmental factors. Results showed sex and age did not influence HCC (sex; P = 0.13, age; P = 0.18), while site location did (P < 0.01). We then modeled HCC from the 24 managed sites as a function of two site variables that could influence HCC: herd density (deer/km2) and urbanization (presence of roads, buildings, vegetation), and found neither had a significant effect. In conclusion, HCC is correlated to BCS and is a non-invasive metric of health. Herd density, if left unmanaged (Objective 1), is a more important driver of individual health than degree of urbanization.