The citrus-like scent of crested auklets: reviewing the evidence for an avian olfactory ornament

Abstract

The body odor of birds has the potential to alter fundamentally our interpretation of avian social behavior by challenging the traditional view that conspecific interactions are primarily guided by sight and sound. Here, I review studies of the crested auklet (Aethia cristatella), a socially monogamous seabird with a seasonally elevated citrusy scent associated with an unusual display behavior. Work on A. cristatella includes investigations of chemistry, social function, and adaptive value of odor. Several lines of evidence are consistent with the notion that odor acts as an olfactory ornament. First, birds exhibit a conspicuous, seasonal display (the “ruff-sniff”) that focuses on scented nape plumage, enabling odor transmission and possibly scent assessment or scent marking. Second, similar to visual ornaments such as facial crests, odor is produced shortly before the breeding season and is lost by the end. Third, crested auklets recognize and are attracted to both natural plumage odor and synthetic mixtures of chemical components. Finally, individuals respond more to male models treated with synthetic odor compounds than to scented female models or unscented controls, suggesting an emphasis of odor in social contexts involving a male. It is presently unclear whether auklet odor effectively deters ectoparasites or acts as an “honest signal” of individual quality, though odor emission rates vary between individuals and concentration appears to correlate with social rank in captivity. Future investigations are needed to reveal whether odor concentrations that mimic a single individual can protect against parasites or pathogens, as are studies of the relationship(s) between scent and secondary sexual traits, such as facial crest length. Such data promise to provide insight into the adaptive value and social function of odor.