Effects of paternal care on reproductive success in the polygynous spotless starling Sturnus unicolor

For males of socially polygynous avian species like the spotless starling, there may exist a trade-off between investing in paternal care and controll ing several nests. To determine how the intensity of paternal care affects reproductive success per brood sired or expressed as the total number of yo ung raised in all nests controlled by the same male, it is necessary to man ipulate paternal care. Testosterone (T) has been shown to depress the tende ncy for males to care for their young, and induces them to acquire more mat es. The effects of paternal care on reproductive success were studied by tr eating certain male starlings with exogenous T and others with the antiandr ogen cyproterone acetate (CA), and comparing the parental behavior of T- an d CA-males throughout the breeding season with that of controls. CA-males f ed their chicks more during the first week after hatching than T-males, wit h controls feeding at intermediate rates, both on a per nest basis and as t otal effort for all nests controlled by the same male. Paternal feeding rat es during the first week of chick life had a significant positive effect on the number of fledged young. The hormone treatment significantly affected the number of chicks raised per nest, CA-males having a higher breeding suc cess per nest than T-males, and controls showing intermediate levels of suc cess; There was no significant effect of treatment on total reproductive su ccess attained by males throughout the season. In the polygonous spotless s tarling, the intensity of paternal care of young affects reproductive succe ss per nest positively but not on a seasonal basis.