Need and nestmates affect begging in tree swallows |
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Authors: | Marty L Leonard Andrew G Horn |
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Institution: | (1) Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4J1 e-mail: MLeonard@is.dal.ca, Fax: +1-902-494-3736, CA |
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Abstract: | We conducted an experiment on nestling tree swallows (Tachycineta bicolor) to examine predictions from signalling models for the evolution of conspicuous begging behaviour. Specifically, we examined
the relationship between (1) nestling begging intensity and hunger, (2) begging intensity and parental provisioning and (3)
begging intensity and nestmate condition. Forty broods of 9-day-old nestlings were removed from their nests for 1 h and assigned
to one of the following three treatments: (1) all nestlings in the brood deprived of food (n = 13), (2) all nestlings in the brood fed (n = 11) or (3) half the nestlings in the brood deprived and half fed (n = 16). Videotapes before and after the treatments showed that begging intensity increased in broods in which all of the nestlings
had been deprived and decreased in broods in which all of the nestlings had been fed. Deprived nestlings in the half-and-half
treatment did not change their begging intensity in response to treatment, while fed nestlings in this treatment group showed
a decrease in begging intensity. Parent tree swallows increased their feeding rate to deprived broods and decreased their
rate to fed broods. Within broods, parents decreased their feeding rate to fed nestlings, but showed no significant change
in feeding to deprived nestlings. Our results suggest that begging intensity is influenced by hunger and that parents appear
to respond to variation in begging intensity. The begging of nestmates also appears to influence begging independently of
need. These results are consistent with predictions derived from signalling models of begging.
Received: 20 June 1997 / Accepted after revision: 19 January 1998 |
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Keywords: | Begging Signalling Sibling interactions Tachycineta bicolor |
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