Male parental investment reflects the level of partner contributions and brood value in tree swallows
Biparental care presents an interesting case of cooperation and conflict between unrelated individuals. Several models have been proposed to explain how parents should respond to changes in each other’s parental care to maximize their own fitness, predicting no change, partial compensation, or matching effort as a response. Here, we present an experiment in tree swallows (Tachycineta bicolor) in which we increased the offspring provisioning of females by presenting them, but not their mates, with additional nestling begging calls using automated playbacks. We performed this experiment in two populations differing in future breeding opportunities. We found that in response to a temporary increase in female parental effort, males in the northern population (with lower future breeding opportunities and thus higher brood value) matched the increased effort, whereas males in the southern population did not. We also found that increases in parental care during playbacks were driven by the females (i.e., females initiated the increased effort and their mates followed them) in the northern population but not the southern population. These results support the idea that with incomplete information about the brood value and need, cues or signals from the partner might become important in coordinating parental care.
Male tree swallows increase parental effort when their mates need to work harder. Using an automated system, we broadcast playback of hungry nestling calls only when the female parent was visiting the nest. In a population where the value of the current brood was high, males significantly increased their provisioning rate, much more than their partners did. Since only the females could hear the playbacks, and the begging of the nestlings did not change in response to the treatment, we suggest that either the males used their partner’s feeding rate as a cue or the females may have communicated to their mates that they should work harder. These results suggest that cues or signals from the partner may be important in coordinating parental care.
KeywordsBiparental care Parental effort Negotiation Sexual conflict Tree swallow
We are grateful to Alice Domalik, Pria St. John (Queen’s University), and Drew Gill and Spencer Gill (Davidson College) for excellent help in the field and for Fruzsina Demcsák (University of Debrecen) for analyzing the begging recordings. We thank Katharina Mahr, the associate editor Marty Leonard, and anonymous reviewers for comments on previous versions of the manuscript.
ÇA and ÁZL designed and coordinated the study, collected field data, carried out data analysis, and drafted the manuscript; MS collected field data and helped draft the manuscript; MFH contributed to the design of the study and helped draft the manuscript; FB collected field data, contributed to the design of the study, and helped draft the manuscript; ITM contributed to the design of the study and helped draft the manuscript. All authors gave final approval for publication.
This work was supported by a U.S. National Science Foundation (NSF) grant (FB, ITM and MFH; IOS-1145625) and by the Natural Sciences and Engineering Research Council of Canada Discovery Grant (FB). During the preparation of the manuscript, ÁZL was supported by grants from the National Research Development and Innovation Office (OTKA K113108 and TÉT_15-1-2016-0044) and by the Romanian Ministry of Education (PN-III-P4-ID-PCE-2016-0572).
Compliance with ethical standards
We confirm that the procedures used in the study followed the guidelines for animal care outlined by Animal Behaviour Society and Association for the Study of Animal Behaviour and were approved by approved by the Institutional Animal Care and Use Committee at Virginia Tech (#12–020) and Animal Care Committee of Queen’s University (#2013-019) and the Canadian Wildlife Service (#CA0211). The field research was conducted with a permit from US Geological Survey Bird Banding Laboratory to MS (#22742) and Canadian Wildlife Service permit to FB (#10771).
Conflict of interest
The authors declare that they have no competing interests.
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