Activity periods and energetic reserves of the brown lemming in northern Alaska

Radiotelemetry provided data on the activity periods of brown lemmings Lemmus sibiricus in northern Alaska. Activity inside the burrow and inactivity outside the burrow usually occurred in short episodes (<3 min), whereas periods of activity outside the burrow and inactivity inside the burrow were more prolonged and appeared to be associated with foraging (outside) and sleeping (inside). Energetic reserves for lemmings entering a burrow consisted of body fat and undigested gut contents, which allowed minimal survival times of 8.6 ± 2.3 h (mean ± 1 S.E.). Nevertheless, lemmings usually left their burrows within 40 min of entering, at which time their stomachs would be at least two-thirds empty. Activity patterns of lemmings appear to change in response to predators, weather and nutritional requirements. We argue that lemmings seek to minimize the time spent foraging rather than to maximize the net energy gain while foraging.