Is there a trade-off between caring for offspring and territorial aggression in tropical male rufous-collared sparrows (Zonotrichia capensis)?

Abstract

Sex-specific fitness costs and benefits influence the degree of offspring care provided by birds exhibiting biparental care. As males typically invest less initially into reproduction, they are more likely to trade-off time and energy spent on paternal care for alternative activities such as aggressive territorial defense. Trade-offs between male territorial aggression and male provisioning are well studied in temperate-zone species, but tropical studies are lacking. Tropical passerines may show distinct trade-offs that influence investment in offspring care, given life history differences such as lower fecundity, slower offspring development, and higher adult survival. We studied trade-offs between paternal care and aggression in an equatorial population of rufous-collared sparrows ( Zonotrichia capensis ). We hypothesized that males with high territorial aggression would be poor providers. To test this we conducted provisioning observations and simulated territorial intrusions on males during three nestling periods. No direct trade-offs existed between aggression and paternal provisioning. Males provisioned at a lower rate than females overall and nestling body size was positively related to male provisioning rates, suggesting a time/energy trade-off between male and female care. Males may, therefore, invest most into alternative activities. However, males stand to gain fitness benefits from provisioning offspring at a relatively high rate.