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.
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)
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).
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
& 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
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.