The fragrant aldehydes are produced in specialized glands, and they are released from wick-like feathers located in the upper back. Douglas explains: “Prospective mates rub bill, breast, head, and neck over wick feathers of their partners. This distributes aldehydes over the head, neck, and face where the birds cannot self-preen. The resulting chemical concentrations are sufficient to deter ectoparasites. Auklets that emit more odorant can transfer more defensive chemicals to mates and are thus more sexually attractive.”
Octanal is a minor constituent (less than 1%) of tangerine, orange, grapefruit and other citrus oils. One of the “other compounds” produced by crested auklets is (Z)-2-decenal, which is the major constituent of coriander leaf oil. The related whiskered auklet (Aethia pygmaea) also produces a fragrance, consisting mainly of heptanal (also found in narcissus absolute) and nonanal (citrus oils again). Finally, in case you’re wondering, emu oil is made from emu fat, and is not a fragrant oil.
There is no evidence that birds are attracted to fragrant plants, and perhaps no reason they would be unless they are looking for seeds that contain essential oil. All birds have functioning olfactory systems, so it remains a possibility. In the meantime, crested auklets have cornered the aerial market for both fragrance and cuteness. Long before Coco Chanel, they discovered the functional beauty of fatty aldehydes.
Douglas HD 2006 Measurement of chemical emissions in crested auklets (Aethia cristatella). Journal of Chemical Ecology 32:2559-2567
Douglas HD 2008 Prenuptial perfume: alloanointing in the social rituals of the crested auklet (Aethia cristatella) and the transfer of anrthopod deterrents. Die Naturwissenschaften 95:45-53
Douglas HD, Co JE, Jones TH et al 2001 Heteropteran chemical repellents identified in the citrus odor of a seabird (crested auklet: Aethia cristatella): evolutionary convergence in chemical ecology. Die Naturwissenschaften 88:330-332
Douglas HD, Co JE, Jones TH et al 2004 Interspecific differences in Aethia spp. auklet odorants and evidence for chemical defense against ectoparasites. Journal of Chemical Ecology 30:1921-1935
Douglas HD, Co JE, Jones TH et al 2005 Chemical odorant of colonial seabird repels mosquitoes. Journal of Medical Entomology 42:647-651
Hagelin JC, Jones IL, Rasmussen LE 2003 A tangerine-scented social odour in a monogamous seabird. Proceedings. Biological Sciences 270:1323-1329