Parent-absent begging in the Brown-headed Cowbird (<Emphasis Type="Italic">Molothrus ater</Emphasis>): the role of short-term need and nestmate size |
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Authors: | James W Rivers |
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Institution: | (1) Department of Ecology, Evolution, and Marine Biology, University of California–Santa Barbara, Santa Barbara, CA 93106-9610, USA |
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Abstract: | Although it is well-established that nestlings of many altricial species beg when parents are away from the nest, we have
a poor understanding of parent-absent begging in brood parasites, including the proximate factors that may influence begging
frequency and intensity. In this study, I examined how parent-absent begging was influenced by competitive asymmetries between
host and Brown-headed Cowbird (Molothrus ater) nestlings under disparate levels of short-term need. Food-deprived cowbird nestlings begged more frequently and for a greater
proportion of parent-absent period than when food-supplemented, with similar patterns observed in hosts of different sizes.
In contrast, three metrics of cowbird begging intensity varied relative to host size but not due to differences in short-term
need. Cowbirds consistently begged more frequently and intensively than host nestlings for a given level of short-term need,
providing evidence that cowbird begging displays are more frequent and intense than non-parasitic nestlings during both feeding
visits and parent-absent periods. In sum, the frequency of begging by cowbirds was only influenced by short-term need, whereas
begging intensity during parent-absent events was only influenced by the host against which cowbirds competed. This study
demonstrates that host size and short-term need had differing influences on the frequency and intensity of parent-absent begging
in cowbirds, although both factors are likely important in limiting the evolution of parent-absent begging in cowbirds. Because
it appears to provide no immediate benefits yet may decrease fitness, parent-absent begging should be included in future theoretical
models investigating the evolution of begging displays in nestling birds. |
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Keywords: | Parent-absent begging Molothrus ater Brown-headed Cowbird Generalist brood parasite Begging |
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