Feeding preference of brown lemmings (Lemmus trimucronatus) for plant parts of Arctic willow (Salix arctica)

Food availability has been proposed to be a factor driving population fluctuations of lemmings in the Arctic. In contrast with previous studies, a recent analysis of faecal pellets and stomach contents of brown lemmings (Lemmus trimucronatus) reported a surprisingly high proportion (34–56%) of willows (Salix spp.) in their diet during both summer and winter in the Canadian high Arctic. To better understand the contribution of willows to the diet of lemmings, we designed a cafeteria experiment to determine which part of Arctic willows (S. arctica), usually the most abundant willow in the Canadian Arctic, were preferred by lemmings. We designed two types of experiments, one with flowering willows (summer stage; n = 10) and one with dormant willows without flowers or leaves (winter stage; n = 11). Lemmings preferred buds and to a lesser extent roots over woody stems in dormant willows, whereas in flowering willows, they preferred flowers and roots over leaves and buds. Our results suggest that lemmings shift their diet seasonally and prefer the fleshiest willow parts, i.e. flowers in summer and buds in winter. High consumption of roots by lemmings in both types of experiments indicates strong underground feeding habits. This behaviour could be favoured by geomorphological processes such as soil upheaves and permafrost thawing that often expose roots to grazing.