Seasonal Changes in the Social Organization of Male Stoats, Mustela erminea: An Effect of Shifts between Two Decisive Resources

A change in male social organization is expected when the most important resource during the breeding season (receptive females) has different dispersion and predictability characteristics as compared with the most important resource during the nonbreeding season (usually food). Male stoats showed a marked seasonal shift in their social organization from a pattern of intrasexual territories during the non-breeding season (autumn and winter) to a non-territorial pattern with extensive and overlapping ranges during the mating season (spring and summer). This shift could not be explained by changes in food availability or distribution, but was correlated instead with the onset of breeding. The proposed hypothesis, that a change in social structure is caused by a shift of decisive resources, will explain seasonal shifts in the social organization of several other mammalian species.