Chemical fingerprints indicate group membership in a highly social communal breeding bird

Gregarious species must distinguish group members from non-group members. Olfaction is important for group recognition in mammals but rarely studied in birds, despite birds using olfaction in social contexts from species discrimination to kin recognition. Olfactory-based recognition requires that groups have a signature odour, so we tested for preen oil and feather chemical similarity among group-living smooth-billed anis (Crotophaga ani). Physiology affects body chemistry, so we also tested for an effect of egg-laying competition, as a proxy for reproductive status, on female chemical similarity. Finally, the fermentation hypothesis for chemical recognition posits that host-associated microbes drive host odour, so we tested for covariation between ani chemicals and microbiota. Group members were more chemically similar than non-group members, regardless of body region, demonstrating that gregarious bird species can have group chemical signatures. Females in groups with less egg-laying competition had more similar preen oil, but not feather, chemicals, suggesting preen oil conveys information about reproductive status. There was no overall covariation between chemicals and microbes; instead, subsets of microbes could mediate olfactory cues in birds. Preen oil and feather chemicals showed little overlap, suggesting they convey different information. These findings will guide experimental work on olfaction in gregarious birds.

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