COMMUNAL NESTING AND COMMUNAL NURSING IN-HOUSE MICE, MUS-MUSCULUS-DOMESTICUS

The functional significance of communal nesting and nursing is poorly understood. Female house mice often communally nest, and within these communal nests females appear to indiscriminately nurse all pups, a ra re trait for any mammal. In this study, the hypothesis that communal n esting provides protection from conspecific infanticide was tested and supported in semi-natural populations of house mice. Conspecific infa nticide in single-mother nests (69%, N=412) was twice that in communal nests (33%, N=508). Because this major benefit of communal nesting do es not require communal nursing, direct benefits to communal nursing i tself were tested. Most proposed benefits should result in heavier wea ning weights, but no differences were found between communal and singl e nests in the semi-natural populations. If communal nursing is to be avoided in communal nests, dams must recognize their own pups. Retriev al tests conducted in the laboratory produced equivocal results. Dams discriminated between pups that differed in age, but not between their own and other age-matched pups. The major survival advantage of commu nal nesting, coupled with the failure to find nutritional advantages f or communally nursed pups, supports a recent suggestion that communal nursing is an unavoidable consequence of communal nesting. This hypoth esis is further strengthened by data indicating that communal nesting partners tend to be kin, thereby providing inclusive fitness benefits to communal nursing. Although costs of communal nursing were proposed and tested, no such costs were found. We also show from 15 observation s of infanticide that all classes of adults (territorial and non-terri torial males, pregnant and non-pregnant females) are infanticidal. The se observations are in conflict with previous laboratory studies. (C) 1995 The Association for the Study of Animal Behaviour