Influence of urban environments on black bear populations and foraging behaviour

Abstract

For most large carnivores, the impact of human development on their population is poorly understood. American black bears (Ursus americanus) use urban environments to forage, often resulting in negative human-bear interactions and management removal of conflict bears. There is a general consensus that available human food sources are the underlying cause of human-bear conflict, but the subtle patterns of how bears use urban resources and the impact that using these resources has on the population is poorly understood. My research focused on understanding how available human foods and management actions in urban environments influence black bear foraging behavior and populations. The National Wildlife Research Center, Colorado Parks and Wildlife and Colorado State University collaborated six year urban bear study in Aspen, Colorado. The overall goal of the study and the objectives of my research questions were to better understand how bears use urban food resources and the influence that these resources have on their population, so that better management practices can be developed. In Chapter 1, I focus on the impacts that natural food failure, available human food, and management removal of conflict bears has on population. Chapter 2 describes general foraging patterns and models resource use in the urban environment at a fine spatial scale. A brief chapter summary, finding, and then management implications are given below. In Chapter 1, we developed a stochastic projection matrix model parameterized with data from the literature and the 6 years of study (2005-2011) in Aspen, Colorado to evaluate the positive and negative influences of urban environments on bears. We modeled the influence that failure of natural food sources, available human food, and different levels of conflict-bear removals could have on a bear populations by comparing a scenario where bears to not benefit from human food sources or experience conflict-bear removals with two urban scenarios where bears have access to human foods, but conflict-bears are removed. Perturbation analyses were used to evaluate consequences that changes to population vital rates could have. We found that the benefit increased cub production from after natural food failure years from available human food sources was quickly negated if conflict-bear management removals reduced adult female survival. Increasing frequency of natural food production failure years resulted in greater impacts from available urban food and conflict-bear removals. Our findings suggest that managers may need to utilize non-lethal practices in managing conflict-bears and municipalities will need to secure human food sources to avoid management removals and population declines. In Chapter 2, we used GPS radio-telemetry data and information obtained from visiting bear foraging locations in Aspen, Colorado from 2007-2010 to determine the food resource bears were using and what factors influenced anthropogenic foraging events. We used a resource selection study design to evaluate fine-scale foraging behavior during prehyperphagia and hyperphagai. Overwhelmingly garbage was the main resource bears used and modeling efforts determined that selection of foraging sites was not only influenced by the presence of garbage but also by the proximity to riparian habitat and presence of ripe fruit trees. We documented inter- and intra-annual foraging patterns of bears foraging extensively in urban areas when natural food sources were not available and switch back to natural food sources when they became available. These patterns suggest that bears balance an energy budget and individual safety when making foraging decision. We suggest management action focus on reducing available human foods to make the urban environment less energetically beneficial for foraging than natural habitat. Management efforts should be prioritized and focus on securing garbage and replacing anthropogenic fruit trees with non-fruiting varieties especially near riparian habitat.