Delineating the ecological and geographic edge of an opportunist: The American black bear exploiting an agricultural landscape

Determining habitat requirements for the persistence of a wildlife population is especially difficult for wide-ranging, opportunist species. The American black bear (Ursus americanus) is one such species that is re-colonizing parts of its former range and colonizing new geographic regions. We sought to predict the potential for further westward expansion of a population of black bears that has recently colonized a primarily agricultural (>50%) landscape with small fragmented islands of forest (∼17%) at the edge of its range in northwestern Minnesota. We delineated critical aspects of bears’ spatial ecology by examining size and habitat composition of home ranges of GPS-collared individuals (n = 38; 75 bear-years; 2007–2013) at both annual and weekly temporal scales. We measured food production by habitat type, and used a moving window equivalent to a weekly home range (WHR) to quantify and map habitat suitability across the region, considering temporal variations in observed natural forage availability. Male bears used expansive home ranges on an annual basis (largest recorded for this species; 95% KDE h-ref: X¯ = 834 km2, 95% CI = 596–1072 km2); females traveled less, but still had relatively large home ranges (95% KDE h-ref: X¯ = 91 km2, 95% CI = 55–128 km2). Summer and fall WHRs contracted when they included higher percentages of oak forest or crop cover (key foods), and expanded with a higher density of roads and higher percentage of non-consumable agriculture and wetlands (i.e., unused areas embedded in the home range). Caloric density had the strongest negative influence on WHR size. We predict males can expand farther westward by virtue of their adaptable, sprawling home ranges that can encompass an array of resources, and their inclination to tolerate and exploit landscapes with few other bears and patchy vegetative cover, embedded with agriculture, roads, and people. Females are more limited to woodlots with natural foods and less apt to be located in open treeless expanses. However, we observed wide year-to-year variations in food production and found that during the most favorable conditions, females could be enticed farther westward, although it is unclear whether they would settle in an environment with even less tree cover than in the current extremity of their range.