Brighter is better: bill fluorescence increases social attraction in a colonial seabird and reveals a potential link with foraging.

Crested auklets (Aethia cristatella) are colonial seabirds with brilliant orange bills during the breeding season. We characterized the bill pigment with spectroscopy methods (resonance Raman, fluorescence, absorbance). We excluded carotenoids as a possible chromophore and showed that the pigment most closely resembles pterins. Like pterins the bill pigment fluoresces, and it occurred in two phenotypes that may differ geographically, perhaps due to environmental heterogeneity. The pigment is unique in the Genus Aethia, and its spectra did not match any known molecule. The UV-Vis absorbance spectrum of the bill pigment overlaps with the extracted pigment of euphausiids, a favored food of crested auklets. A color preference associated with prey may have favored characteristics of the crested auklet's accessory bill plates. Crest size, a signal of dominance, tended to correlate positively with highest fluorescence in the single-band phenotype. Brighter bills may function in self-advertisement and verify the status signal of the crest ornament. We tested for a behavioral preference using identical decoys that differed only in bill fluorescence. Crested auklets approached models with fluorescent bills at a higher frequency. In cases where sex of crested auklets was known, males responded at a higher frequency to fluorescent bills, but females did not. In an evolutionary context, bill fluorescence could have conferred an advantage in social interactions, e.g., in dimly lit rock crevices. Bill brightness and color may communicate success in foraging and may function as an honest signal of mate quality.

An Extraordinary Host-Specific Sex Ratio in an Avian Louse (Phthiraptera: Insecta)--Chemical Distortion?

Distortions of sex ratios and sexual traits from synthetic chemicals have been well documented; however, there is little evidence for such phenomena associated with naturally occurring chemical exposures. We reasoned that chemical secretions of vertebrates could contribute to skewed sex ratios in ectoparasitic insects due to differences in susceptibility among the sexes. For example, among ectoparasitic lice the female is generally the larger sex. Smaller males may be more susceptible to chemical effects. We studied sex ratios of lice on two sympatric species of colonial seabirds. Crested auklets (Aethia cristatella) secrete a strong smelling citrus-like odorant composed of aldehydes while a closely related congener the least auklet (Aethia pusilla) lacks these compounds. Each auklet hosts three species of lice, two of which are shared in common. We found that the sex ratio of one louse species, Quadraceps aethereus (Giebel), was highly skewed on crested auklets 1:69 (males: females), yet close to unity on least auklets (1:0.97). We suggest that a host-specific effect contributes to this difference, such as the crested auklet's chemical odorant.

Chemical odorant of colonial seabird repels mosquitoes.

The crested auklet, Aethia cristatella, emits a class of aldehydes shown to be potent invertebrate repellents when used by heteropterans against their predators. Our aim was to determine the efficacy of these aldehydes against mosquitoes in the laboratory. Synthetic analogues of the auklet odorant were strongly repellent to mosquitoes in controlled laboratory trials. Furthermore, the efficacy was similar to previous reports for commercial mosquito repellents. These results, in combination with a previously published study, show that constituents of the aldehyde odorant are broad spectrum in efficacy against ectoparasitic arthropods of birds. Our report is the first empirical evidence for an endogenous mosquito repellent in birds.

Heteropteran chemical repellents identified in the citrus odor of a seabird (crested auklet: Aethia cristatella): evolutionary convergence in chemical ecology.

The exogenous application of chemical repellents is widespread in birds, but endogenous production is exceedingly rare. We herein report a new class of avian defensive compounds isolated from the feathers and volatile odor of the crested auklet (Aethia cristatella). Mass spectra indicate that n-hexanal, n-octanal, n-decanal, Z-4-decenal and a 12-carbon unsaturated aldehyde comprise the auklet odorant. Octanal and hexanal are also secreted in the repugnant metasternal gland emissions of heteropteran insects and are known to be potent invertebrate repellents. We suggest that the auklet odorant functions as an ectoparasite repellent and a signal of mate quality. This would represent a rare and direct link between vigor, quality and parasite resistance, one of several putative bases for mate selection. This is the first report of defensive compounds produced by a seabird or colonial bird and one of the few examples of chemical defense in a polar or subpolar marine vertebrate.