SOCIAL STIMULATION AND REGULATION OF BODY-MASS IN FEMALE STARLINGS

The influence of consexual social stimulation on the regulation of bod y mass in female European starlings, Sturnus vulgaris, during reproduc tive development was examined. Twenty-four pairs of birds were housed in three social stimulation treatments: (1) control, where birds were housed in visual isolation from their partner; (2) visual contact, pai rs of birds were separated by a clear Perspex screen, preventing direc t physical contact, but allowing birds to view each other; (3) complet e contact, pairs of birds were housed with no intervening divider, all owing full interactions between birds. The influence of these treatmen ts on gonadal development, body mass and energetic reserves was examin ed. The manipulation did not significantly influence degree or rate of gonadal development, but did influence total body mass; birds from th e complete contact group increased body mass to a greater extent than the other groups. This between-group difference was attributable to ch anges in lean mass, rather than energetic reserves. However, within th e complete contact group, subdominants increased their energetic reser ves more than dominants. These results are, in part, consistent with d ifferences in competition for food between the treatment groups influe ncing mass regulation, although changes in activity levels may also be important. Unlike previous studies, these results suggest that the so cial environment may influence the regulation of lean mass in addition to energetic reserves. (C) 1997 The Association for the Study of Anim al Behaviour.