Ecology of American Black Bears in an Urban Environment

Gould, Nicholas

ABSTRACT: Cities now constitute one of the most rapidly growing ecosystems in the world, and with the global spotlight on increasing urbanization and development, the focus on wildlife in ‘natural’ systems is sharing importance with a focus on wildlife in urban systems, providing unique research opportunities in ecology and conservation. Over four years from April 2014 through June 2018, we investigated the effects of urban development and natural food production on American black bear (Ursus americanus) ecology centered on the city of Asheville, North Carolina. Black bears are model animals for study because they are behaviorally flexible omnivores highly adapted to locate and secure high calorie foods and, thus, may benefit from a variety of urban resources. In chapter 1, we present research on the early growth and reproduction by urban and rural black bears in Asheville, North Carolina, and in 3 nearby rural sites. We used trapping in spring and summer and used winter den visits to assess reproduction by young female black bears. Urban yearling females weighed more than yearling females from the three rural study sites, and 2-year old urban female bears produced cubs, but no 2-year old rural females produced cubs. We hypothesize that reproduction by 2-year old bears may be linked to the permanence of anthropogenic food sources associated with urban environments. To inform population level management decisions further, managers and researchers should quantify urban food sources and the effects on black bear life history. If high population fecundity allows urban populations to sustain relatively high mortality rates, then urban bear populations may be source populations for surrounding, rural areas. In chapter 2, we present research on the spatial ecology of urban and rural American black bears in North Carolina. Black bears in rural areas are known to shift their spatial distributions in response to available resources but limited information is available on how bears move through developed environments beyond the bears’ use of urban areas in years of poor production of natural foods. We used continuous time movement models to estimate annual and seasonal home range sizes to compare bears occupying developed areas (urban bears) and those in undeveloped areas (rural bears). Urban bears had consistently smaller home ranges than rural bears, regardless of variation of natural food production. Furthermore, home range size for urban bears did not vary with housing density or with natural food production. This result suggests that urban areas may be good habitat for bears where they can meet their metabolic requirements and secure adequate resources across the full range of housing development present in our study area. In chapter 3, we present research on the effects of housing density and road density on the selection of den sites by black bears. We documented that urban bears did not avoid areas with housing or roads at the level of the study area (2nd order) or within the home range (3rd order). At the finer scale (3rd order), slope was the best predictor of den site selection. At both scales of den site selection, we detected no relationship with elevation or land cover type. Median den entry and emergence dates for bears were the third week in December and the third week in March. Reuse of den sites was low, suggesting that dens are not a limiting resource for urban bears in Asheville, North Carolina. Collectively, our results indicate that selection of den sites by black bears in urban areas may not be as critical to their fitness as it is to their rural counterparts.