Wax Ester Composition of Songbird Preen Oil Varies Seasonally and Differs between Sexes, Ages, and Populations
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Chemical signaling has been well studied in invertebrates and mammals but less so in birds, due to the longstanding misconception that olfaction is unimportant or even non-existent in this taxon. However, recent findings suggest that olfaction plays an important role in avian mate choice and reproductive behavior, similar to other taxa. The leading candidate source for compounds involved in avian chemical communication is preen oil, a complex mixture secreted from the uropygial gland. Preen oil contains volatile compounds and their potential wax ester precursors, and may act as a reproductive chemosignal. Reproductive signals are generally sexually dimorphic, age-specific, seasonally variable, and may also vary geographically. We tested whether preen oil meets these expectations by using gas chromatography to examine the wax ester composition of preen oil in song sparrows (Melospiza melodia). We found that the wax ester composition of preen oil was significantly different between sexes, age classes, seasons, and populations. Collectively, our results suggest that song sparrow preen oil meets the criteria of a chemical cue that may influence mate choice and reproduction. Our findings in song sparrows, which are sexually monomorphic in plumage, also parallel patterns described for dark-eyed juncos (Junco hyemalis), a closely related songbird with sexually dimorphic plumage. Behavioral tests are needed to confirm that song sparrows attend to the cues present in preen oil, but our findings support the increasingly accepted idea that chemical communication is common and widespread in birds as it is in other taxa.
KeywordsInfochemicals Melospiza melodia Preen oil Reproductive chemosignal Chemical communication Song sparrow Uropygial gland
We thank the rare Charitable Research Reserve and the Queen’s University Biological Station (QUBS) for access to their land and research facilities. We further acknowledge that the land we used is on the traditional territories of the Anishinabek and Haudenosauneega (Iroquois) peoples, Haldimand Treaty and Simcoe Patent Treaty lands (Cambridge) and on the traditional territories of the Anishinabek, Huron-Wendat, and Mohawk peoples and Crawford Purchase lands (Newboro). We thank Tosha Kelly and Ross Dickson for field assistance and sample collection. This research was supported by an Ontario Graduate Scholarship and a Vanier Scholarship to LAG, and NSERC Discovery Grants to MAB and EAMS.
Compliance with Ethical Standards
All birds were captured under permission from the Canadian Wildlife Service (banding subpermits 10691B, E, F). All animal procedures were approved by The University of Western Ontario Animal Use Subcommittee (protocol # 2016–017).
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