Avian Olfaction

For many years, birds were thought to have poor senses of smell, an assumption drawn from the relatively small and simple avian olfactory bulb (Waldvogel 1989). However, more recent research has introduced us to the complexity and depth of the avian sense of smell. The initial breakthrough was made by Bang (1960), who suggested that birds in certain ecological niches might have a more developed sense of smell than previously thought. Birds with high olfactory ratios were typically ground-dweling carnivores, small New-World Vultures, or marine birds: kiwis, Turkey Vulture, tubenoses (Procellariiformes) (Bang & Wenzel 1985, Evans & Heiser 2001). Bang's research sparked a wave of olfaction research that has broadened the horizons of the understanding of how birds smell.

Kiwis: small, ancestral, flightless, noctornal carnivores found in the forests of New Zeland - have what is possibly the best avian sense of smell. Their olfactory lobe is ten times the size of other birds and nostrils are located at the bill tip, rather than at the base of the bill (where they are found on all other birds). Kiwis use their bill to probe for worms and bugs in the soil and are capable of locating food by smell alone, although they also have a well-developed sense of hearing. (Evans & Heiser 2001, Gill 1995, Wenzel 1968)

Procellariformes: tubenoses- albatrosses and petrels - pelagic (0pen ocean) birds with well-developed, tubular nostrils. Tubenoses use olfactory cues to forage and also to return to their burrows over many kilometers. They are attracted to fish oil and dimethyl sulfide, volatile compounds released by dead fish and the plankton that feed upon them. Smaller species, those that feed upon plankton, arrive first at most odor sources, and appear to have to best-developed sense of smell. Procelliformes also are capable of using smells to locate their burrows at night, locating individual nests by smell. (Bonadonna et al 2001, Evans & Heiser 2001, Gill 1995, Nerill 1999, Verheyden & Jouventin 1994).

New-World Vultures: different from Old-World Vultures (which are closely related to eagles), New-World Vultures (Cathartidae) which may be more closely related to storks. Old-World Vultures have very little sense of smell and rely mainly on their keen sense of sight to find carrion. Likewise, the larger New-World species are primarily visual foragers. Smaller species (Turkey, Greater and Lesser Yellow-headed Vulture) are capable of using olfactory cues to locate food and have the enlarged olfactory bulb to go with that ability. Black Vultures and other larger species often use Turkey Vultures as cues to the location of a carrrion source, clouding the issue of which species use olfactory cues. Pipeline engineers have used this ability as well, injecting ethyl mercaptan (an odorant found in carrion) into pipes and following vultures to the leak. (Evans & Heiser 2001, Gill 1994, Kirk & Mossman 1998, Smith and Paselk 1986)

Orientation & Navigation: aside from the previous examples, many other species have been shown to use olfactory cues to forage, home, and migrate. Many of these species appear to be using small-scale olfactory cues for local piloting, but homing pigeons and some migratory birds may be using olfaction for true navigation. While it does not seem to be a primary navigational cue, odors are proving to be important cues in orientation and migration. ( Clark & Mason 2000, Walraff & Andreae 2000, Waldvogel 1989)

While much progress has been made in the last few decades in the study of avian olfaction, there is still much more to find out. Olfaction in species with less developed olfactory neuroanatomy, homing, migration, potential odorants, and the role of pheromones are but a few areas that would benefit from further research. Even so, what little we have learned about birds' sense of smell is tantalizing and has opened up more avenues for resarch.
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