Social stimulation and regulation of body mass in female starlings

The influence of consexual social stimulation on the regulation of body mass in female European starlings, Sturnus vulgarisduring reproductive 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, pairs of birds were separated by a clear Perspex screen, preventing direct physical contact, but allowing birds to view each other; (3) complete contact, pairs of birds were housed with no intervening divider, allowing full interactions between birds. The influence of these treatments on gonadal development, body mass and energetic reserves was examined. The manipulation did not significantly influence degree or rate of gonadal development, but did influence total body mass; birds from the complete contact group increased body mass to a greater extent than the other groups. This between-group difference was attributable to changes in lean mass, rather than energetic reserves. However, within the complete contact group, subdominants increased their energetic reserves more than dominants. These results are, in part, consistent with differences in competition for food between the treatment groups influencing mass regulation, although changes in activity levels may also be important. Unlike previous studies, these results suggest that the social environment may influence the regulation of lean mass in addition to energetic reserves.