Brood provisioning rate and food allocation rules according to nestling begging in a clutch-adjusting species, the Rufous-tailed Scrub-robin Cercotrichas galactotes

Brood reduction may be a strategy by which, when food is scarce, parents provision chicks differentially — this usually leads to the death of the smaller nestlings. In contrast, in species where brood reduction does not normally occur, parents may allocate food equally among nestlings. The Rufous-tailed Scrub-robin Cercotrichas galactotes is a species in which brood reduction does not occur (it is a clutch adjuster), so that all nestlings usually fledge. This study analysed the food allocation rules in this species. As predicted, begging behaviour in nestlings seems to indicate their need for food, because once fed, they reduced their begging levels. Parents provisioning the nest allocated food according to begging by nestlings. Those nestlings that got fed begged nearer the parents, with lower latency and higher intensity, and stretched up to a greater height while begging. Moreover, the feeding rate was higher when more nestlings begged in the nest. There were slight differences between males and females with respect to prey type brought to the nest. Bigger nestlings got a larger proportion of food because they begged more intensely, but there was no evidence of parental favouritism towards bigger chicks.