Sharing of caring: nestling provisioning behaviour of long-tailed tit, Aegithalos caudatus, parents and helpers

The optimal investment strategies of parents in biparental systems are well studied. This contrasts with a poor theoretical and empirical understanding of variation in individual investment in breeding systems with multiple carers. We used the cooperative breeding system of long-tailed tits, to investigate how parents and helpers adjust their rate of nestling provisioning in relation to measures of nestling demand and the number of helpers. Our aim was to examine whether parents and helpers follow the same provisioning rules. Overall provisioning rates were higher for parents than for helpers. However, both parents and helpers increased their provisioning rates as nestlings aged and provisioned at higher rates early in the day. Parents brought more food to larger broods when not helped, but at nests with helpers, neither parents nor helpers had significantly higher provisioning rates at larger broods. However the total provisioning rate was higher at larger broods at both nests with and without helpers. Parents reduced their work rate in response to the arrival of a helper, but neither parents nor first helpers reduced their work rates further with arrival of additional helpers. Variation in provisioning rates between parents and helpers may be the result of different cost-benefit relations, and a theoretical framework is needed within which to explore the consequences of such differences. (C) 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.