Behavioral and physiological responses of American black bears to landscape features within an agricultural region

• Published in: Ecosphere (Washington, D.C) D.C), 2015-03, Vol.6 (3), p.art28-21
• Main Authors: Ditmer, M. A, Garshelis, D. L, Noyce, K. V, Laske, T. G, Iaizzo, P. A, Burk, T. E, Forester, J. D, Fieberg, J. R
• Format: Article
• Language: English
• Subjects: Bears; Behavior; biologger; Biology; Collaboration; Crop fields; Crops; Ecology; GPS; habitat fragmentation; Habitats; Heart rate; Influence; Landscape; Metabolism; Minnesota; Monitoring systems; movement; Organisms; Physiological responses; Physiology; Population; stressors; Travel; Ursus americanus
• ISSN: 2150-8925; 2150-8925
• DOI: 10.1890/ES14-00199.1

Human activities and variation in habitat quality and configuration have been shown to influence space use patterns in many species, but few studies have documented the physiological responses of free-ranging animals to these factors. We combined remote biologger technology, capturing continuous heart rate values, with locational data from GPS collars to investigate the behavioral and physiological reactions of American black bears ( Ursus americanus ) to a landscape dominated by agriculture (52.5% areal cover). Our study occurred at the edge of the range of this species, with small, scattered patches of forest within a mosaic of crop fields and an extensive road network. However, only ~2-4% of the area contained crops that bears consumed (corn, sunflowers, oats). We used GPS locations to identify the habitat that bears occupied, and to estimate their rates of travel. Heart rates increased with movement rates, rising by over 30% from resting rate to their fastest travel speeds. We used a modeling approach to distinguish among factors that influenced heart rates independent of movement rates. Bears commonly crossed agricultural areas that provided no food or cover and their heart rates, elevated beyond what was expected from their movement rate, were indicative of a stress response. However, when bears entered agricultural areas composed of edible crops, many individuals showed reduced movement and slower heart rates, suggesting that bears foraging there felt at ease or crops allow bears to more easily forage due to their dense spatial arrangements. Unexpectedly, female bears elicited lower heart rates and lower levels of activity in the most fragmented patches of natural habitat, possibly a sign of human-avoidance behavior or a reaction related to crossing roads. During fall, as bears prepared for hibernation, their heart rates declined two weeks before their movements slackened, evidence that metabolism slowed to enhance fat accumulation; they also shifted to a nocturnal activity pattern, likely to reduce exertion during the heat of the day. The use of a physiological monitor provided new insights on bear biology and ecology that would not have otherwise been apparent.