Avian olfactory displays: a hypothesis for the function of bill-wiping in a social context
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Bill-wiping, or the scraping by a bird of its bill along a substrate, has been observed in social contexts and cited as an irrelevant displacement activity. However, several behaviors once categorized as displacement behaviors have since been shown to serve adaptive functions. Here, we hypothesize that bill-wiping may function in social interactions by releasing odors from the waxy residue of preen oil on the bill. We assessed behavioral context associated with bill-wiping by comparing the frequency of bill-wiping by free-living male songbirds when presented with a caged male or female conspecific paired with playback; males bill-wiped significantly more often in response in a courtship context and in a mate-guarding context than in a territorial context. Bill-wiping frequency correlated with courtship behaviors, such as tail spreading and singing short-range songs, but not with aggressive behaviors. We also noted attributes of individuals that engaged in bill-wiping during courtship and found that younger, smaller males performed this behavior more frequently than older, larger males. Finally, we conducted a captive Y-maze experiment to test whether dried preen oil residue would be more detectable if it were manipulated (scratched to potentially release odor) or unmanipulated. Preliminary evidence suggests that males could be more responsive to manipulated preen oil, though stronger tests are needed. Taken together, our results suggest a functional hypothesis: bill-wiping during courtship may be an olfactory display that releases odor that may be detected by potential mates and rivals. We conclude by suggesting ways in which future work can test the olfactory display hypothesis.
KeywordsChemical communication Songbirds Preen oil Courtship
We are grateful to Ellen Ketterson for discussion and helpful comments on this manuscript. We also thank Elizabeth Schultz, Stephen Ferguson, Rebecca Koch, and Abby Kimmitt for their assistance in the field. This work was supported by the National Science Foundation (DGR was supported by NSF graduate research fellowship and DDIG IOS-1011145; DJW was supported by Cooperative Agreement DBI-0939454; work was also supported by IOS-0820055 with an REU supplement to Ellen D. Ketterson). We thank Grand Teton National Park, University of Wyoming-National Park Service Research Station, and Mountain Lake Biological Station, University of Virginia.
All work was conducted in compliance with the Bloomington Institutional Animal Care and Use Committee guidelines (BIACUC protocol 09–037 in 2011, protocol 12–050 in 2013) and with permission from the US Department of Fish and Wildlife, the Virginia Department of Game and Inland Fisheries, the Wyoming Game and Fish Department, the US Department of the Interior National Park Service, and the US Forest Service.
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