Brood sex allocation in the neotropical cooperative White-banded Tanager Neothraupis fasciata

Abstract

Sex allocation in cooperative breeding species may be influenced by the return in fitness that parents receive when producing offspring of each sex, especially if helping behavior is sex-specific. Factors such as the presence of helpers assisting the breeding pair, resource availability, and timing of breeding may also influence brood sex ratio. In this study, we evaluated brood sex allocation in a neotropical cooperative breeding, the White-banded Tanager Neothraupis fasciata, which shows a slightly higher numbers of males, the helping sex, in the adult population. We tested brood sex allocation in relation to the presence of helpers in the groups, nest initiation date, and territory quality. At the population level, we found strictly equal numbers of offspring of both sexes. At the individual level, there was no effect of the ecological, environmental, and temporal variables we tested in the sex allocation of tanagers’ offspring. We suggest that brood sex allocation is unlikely to occur in the study species, and that high levels of nest predation may inhibit the development of sex allocation strategies in neotropical open nesting species, such as White-banded Tanager.