Helpers-at-the-nest have the same provisioning rule as parents: experimental evidence from play-backs of chick begging |
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Authors: | Jonathan Wright |
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Institution: | (1) School of Biological Sciences, University of Wales, Bangor, Gwynedd, LL57 2UW, UK e-mail: j.wright@bangor.ac.uk, Tel:+44-1248-382313, Fax: +44-1248-371644, GB |
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Abstract: | Despite the success of kin selection in explaining helping-at-the-nest among communally breeding birds, we know almost nothing
about how helpers regulate their chick-feeding effort. This is especially interesting given how much we now know about parental
provisioning `rules-of-thumb' and the evolution of chick begging as an honest signal of `need'. This study explores the provisioning
rules of helpers and parents in Arabian babblers (Turdoides squamiceps), using tape play-backs to supplement chick-begging signals and increase apparent brood demand. In all eight groups tested,
both helpers and parents fed older, noisier broods at higher rates. Total provisioning rates to nests increased during begging
play-back days compared to control days. Absolute provisioning rates by helpers and the scale of their responses to play-backs
were statistically indistinguishable from those of parents. In both helpers and parents, increases in nest visits during play-backs
were associated with reductions in foraging distance from the nest and increases in size of prey delivered. Older birds of
both sexes delivered slightly larger prey items, possibly reflecting differences in foraging ability due to experience. These
results are consistent with the idea that, like the parents, helpers-at-the-nest in Arabian babblers provision nestlings as
part of a strategy of investment, irrespective of helper age, dominance status or sex. In this species, high relatedness within
groups may provide parents and helpers with similar kin-selected fitness benefits, although the mutualistic advantages to
helpers from simply augmenting group sizes cannot be ruled out.
Received: 17 June 1997 / Accepted after revision: 28 February 1998 |
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Keywords: | Helpers-at-the-nest Parental care Chick feeding Cooperative breeding Arabian babbler Turdoides squamiceps |
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