Interspecific differences in Aethia spp. auklet odorants and evidence for chemical defense against ectoparasites

The true auklets (Genus Aethia) are small planktivorous seabirds of the Bering Sea and North Pacific. Two species, the crested and whiskered auklets produce volatile citrus-like odorants. We here show that the whiskered auklet odorant is composed predominantly of two odd-numbered aldehydes (heptanal and nonanal) with no detectable unsaturated aldehydes. By comparison the crested auklet odorant is dominated by even-numbered aldehydes, both saturated and monounsaturated, ranging in size from 6 to 12 carbons. This is evidence of species-specific acquisition or biosynthetic pathways. We clarify the chemistry of the crested auklet odorant. We cite evidence that the C-12:1 aldehyde in crested auklets is actually two isomers, (Z)-4-dodecenal and (Z)-6-dodecenal. We also report on experimental evidence that aldehyde constituents kill and repel ectoparasites. Efficacy of the aldehydes may increase when they are combined in a mixture. The repellency of the mixture increases with chemical concentration. This suggests that individuals with higher chemical production are likely to repel ectoparasites more effectively.