Birth-site selection and timing of births in American bison: effects of habitat and proximity to anthropogenic features

Abstract

Context Human activities can affect habitat selection by ungulates during parturition. Minimising human–wildlife conflicts during the birthing period can be critical in national and state parks that receive high numbers of human visitors. American bison (Bison bison) are an iconic species in North America, and many conservation herds of bison occupy national and state parks and wildlife refuges. Aims We investigated timing of births and birth-site selection of bison on Antelope Island State Park, Utah, at multiple spatial scales to determine the relative influence of surrounding vegetation, topography and distance to anthropogenic features (i.e. trails, roads or structures) on selection of birthing habitat. Methods We used vaginal implant transmitters to determine timing of births and to identify birth sites of bison. We used logistic regression within a model-selection framework to differentiate between birth sites and random locations, based on potential explanatory variables. We then used model-averaged coefficients to produce and project a GIS model of birthing habitat onto Antelope Island. Key results During 2010 and 2011, we quantified variables surrounding 35 birth sites and 101 random sites. Variables in top models of birth-site selection for bison included landscape curvature and elevation, averaged at a 500-m radius around birth sites, as well as distance to nearest trails, roads or structures. Five-fold cross validation (rho = 0.89; P < 0.05) indicated that these variables successfully predicted birth sites of bison in our study area; 80% of 41 births occurred in April (range = March 22 to May 20). Conclusions Bison selected areas for birthing with concave topography and increased elevation that were away from trails, roads or structures. Implications Our GIS model of birthing habitat, and data concerning timing of births, provide a map of high-probability birthing areas and a time of year at which human access could be limited to reduce disturbance from recreational activity. This approach could aid managers in minimising conflict between recreationists and parturient bison in other national and state parks and wildlife refuges.