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

Abstract

For males of socially polygynous avian spe- cies like the spotless starling, there may exist a trade-off between investing in paternal care and controlling sever- al nests. To determine how the intensity of paternal care affects reproductive success per brood sired or expressed as the total number of young raised in all nests con- trolled by the same male, it is necessary to manipulate paternal care. Testosterone (T) has been shown to de- press the tendency for males to care for their young, and induces them to acquire more mates. The effects of pa- ternal care on reproductive success were studied by treat- ing certain male starlings with exogenous T and others with the antiandrogen cyproterone acetate (CA), and comparing the parental behavior of T- and CA-males throughout the breeding season with that of controls. CA-males fed their chicks more during the first week af- ter hatching than T-males, with controls feeding at inter- mediate rates, both on a per nest basis and as total effort for all nests controlled by the same male. Paternal feed- ing rates during the first week of chick life had a signifi- cant 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 breed- ing success per nest than T-males, and controls showing intermediate levels of success. There was no significant effect of treatment on total reproductive success attained by males throughout the season. In the polygonous spot- less starling, the intensity of paternal care of young af- fects reproductive success per nest positively but not on a seasonal basis.