Seasonal and annual variation in the diet of brown bears Ursus arctos in the boreal forest of southcentral Sweden

Abstract

Understanding a species' feeding ecology is essential for successful management and conservation, because food abundance can influence body mass, survival, reproductive success, movements, and habitat use. We describe annual and seasonal variations in the diet of brown bears Ursus arctos in southcentral Sweden, based on analysis of 527 fecal samples from 1994–1996 and 2000–2001. There was distinct seasonal variation in most of the 26 food items we documented. Ungulates, predominantly moose Alces alces, and insects comprised most of the estimated dietary energy content in spring and summer. Insects were represented almost entirely by ants, of which Formica spp. and Camponotus herculeanus were the most common. During autumn, berries dominated the diet. The most important berry species were bilberry Vaccinium myrtillus, crowberry Empetrum hermaphoditum and lingonberry V. vitis‐idaea. We determined berry availability by inventorying 308 random plots three times for two consecutive years. These three berries occurred with great spatial, seasonal and annual variation in abundance. The bears showed the strongest positive preference for bilberries, a lesser positive preference for crowberries, but no preference for lingonberries. The proportion of berries in the autmn diet was stable between years, but the relative importance of the species changed, indicating that bears switched to crowberries when bilberries were less abundant. The effects of predicted future climatic change might have severe effects on the availability of the berries, which is the only important food available for fat acquisition prior to hibernation.

Habitat segregation between brown bears and gray wolves in a human‐dominated landscape

“…The stronger selection for moose by wolves than by bears was consistent throughout the two study periods and likely reflected differences in the requirements of an obligate carnivore compared to those of the omnivorous bear, whose diet is more diverse (Stenset et al., ). To account for marked seasonal differences in the behavior of wolves and bears and consider the phenology of the main prey and the progressive green‐up of vegetation, we divided our study of habitat selection into late winter and spring (Figure ).…”

“…Wolves are obligate carnivores, and bears are omnivores. In Scandinavia, moose ( Alces alces ) is the staple prey of wolves (Sand et al., , ), whereas the diet of bears includes a wide range of food items (Stenset et al., ). Nevertheless, bears are also efficient predators of neonate moose (Dahle et al., ; Swenson et al., ), and they kleptoparasitize more than half of the wolf kills during spring in central Sweden (Milleret, ; Ordiz et al., ).…”

Berry production drives bottom–up effects on body mass and reproductive success in an omnivore

“…Bilberry Vaccinium myrtillus, lingonberry V. vitis-idaea and crowberry Empetrum hermaphroditum are the most important food resources for bears in Scandinavia during hyperphagia (Stenset et al 2016). Peak fruit production of berries follows regular masting cycles of 2-5 years (Selås 2000) that are altered by weather conditions during crucial stages of berry phenology (Selås 2000, Bokhorst et al 2011, Rixen et al 2012, Selås et al 2015.…”

Fluctuating mast production does not drive Scandinavian brown bear behavior

“…One caveat of our study is that we did not monitor crowberry (Empetrum hermaphroditum) production over the same time period. Berry producing crowberry plants occur least often in our study area (Hertel et al 2016), but nevertheless Stenset et al (2016) report a relatively high fecal volume and frequency of occurrence of crowberry in 1 out of 5 study years. Bears may therefore switch to crowberry in years of low bilberry or lingonberry production.…”

“…An alternative explanation may be that other food resources, like insects or graminoids, buffer food limitation, and thus explain the lack of a behavioral response in Sweden (Mcloughlin et al 2000). We deem this explanation unlikely, given a range of earlier studies confirming that over a range of different study years berries were by far the most important food source for brown bears in southcentral Sweden in the fall (Elfstr€ om et al 2014, Hertel et al 2016, Stenset et al 2016. One caveat of our study is that we did not monitor crowberry (Empetrum hermaphroditum) production over the same time period.…”