Linking winter severity to space use of European bison around feeding sites in Białowieża Primeval Forest (NE Poland)

Abstract

Supplementary feeding is a commonly used wildlife management practice, but while it may bring benefits and fulfil management goals, it can also result in unintended negative consequences. In the temperate zone, winter supplementary feeding may reduce movement of some ungulate species, leading to increased utilization of feeding sites by individuals and, consequently, animal aggregation. However, the intensity of feeding site utilization can vary depending on various extrinsic factors, e.g. habitat type, population density or weather conditions. Here, we predicted that the index of feeding sites utilization, expressed as the distance of European bison (Bison bonasus) to feeding sites, would be positively associated with the severity of winter conditions; thus, bison will be closer to feeding sites on colder days and in the presence of snow cover. We analysed winter (December to March) tracking data of 43 VHF- and GPS-collared European bison (24 males and 19 females) collected from 2005 to 2012 in Białowieża Primeval Forest (NE Poland), where bison are supplementally fed with different intensity throughout winter. Female bison were closer to feeding sites than males throughout winter, and regardless of sex, bison were the closest to feeding sites in mid-winter (January to February) and on colder days independently of the time of the season. Additionally, the distances of bison to feeding sites were significantly related to snow cover and depth; i.e. bison were closer to the feeding sites on days with present snow cover and deeper snow. Hence, the winter area occupied by bison differed with changing weather severity — being 4 and 28 times larger in the warmest periods compared to the coldest days with snow cover (for females and males, respectively). This may have direct and indirect ecological consequences for the ecosystem due to potential impact on nutrient cycling, seed dispersal, interspecific competition, vegetation growth, forest succession and carrion distribution. Given these ecological impacts of bison and weather-dependent utilization of supplementary fodder, we recognize the possible need in the future to revise and adapt winter supplementary feeding to annual and seasonal variation in winter severity to meet management goals while optimizing the costs.