Nest predation versus resources in a Neotropical passerine: Constraints of the food limitation hypothesis

Abstract

Food limitation is one explanation for differences in life-history traits, such as clutch size or nestling mortality, between tropical and temperate birds. Also predation has been considered one of the major factors shaping life-histories. We found mixed support for the food-limitation hypothesis when we experimentally manipulated food abundance and evaluated subsequent effects on breeding and behavioural parameters of the Blue-black Grassquit (Volatiniajacarina). Food-provisioned males increased territorial disputes and received more female visits, and a higher proportion of supplemented pairs produced more eggs and had faster growth rates in their broods compared to non-provisioned pairs. v However, egg laying was delayed in the fed group. Unexpectedly, prédation in the foodprovisioned group was twice that of the control group. We presume that nest detection by predators increased due to higher nest attentiveness in food-provisioned nests. Food availability constitutes a proximate mechanism resulting in changes in behaviours and breeding parameters, but nest predation may be the prevailing selective pressure.