Biology Reference
In-Depth Information
A
American White Pelicans are specialized for feeding in freshwater, usually in shallow
areas of lakes and rivers. If they tried diving into those waters, they'd kill themselves!
Instead, they often group into little squadrons and fish cooperatively, forming a tight line
and, by beating and dipping their wings and bills, herd fish into the shallowest waters
where they can scoop them up.
Brown Pelicans, on the other hand, are marine birds, and although they, too, are ex-
tremely sociable and nest and loaf in large colonies, they don't feed cooperatively. In-
stead, this species has perfected plunge diving. Brown Pelicans can see fish beneath the
surface and can calculate where to dive, correcting for the refraction of light that makes
fish appear in a different place than where they really are. During the dive, they pull their
head in over their shoulders, pull their legs forward, and bend their wings at the wrist.
Interestingly, they also rotate their body to the left, which probably protects their trachea
andesophagusastheyhitthewater.Thesevitalstructuresaresituated ontherightsideof
their neck.
As their bill enters the water, the birds thrust their legs and wings backward, moving
theirbilltowardthefishevenfaster.Theirhugethroatpouchexpandsasitfillswithupto
2½ gallons (9.5 l) of water; the pressure forces the lower bill into a distorted bow shape
but it doesn't break, thanks to special muscle adaptations.
The streamlined upper mandible guides the fish into the mouth, the lower bill bounces
back into shape, and the bird closes its bill, trapping the fish inside the pouch. It raises
the back of its head slowly with the pouch pressed against its breast to drain out the wa-
ter while retaining the fish, then tosses its head up to swallow the fish. If the dive was
unsuccessful, the bird quickly raises its head with the bill open so the water drains out
immediately. It takes less than 20 seconds to drain the pouch and swallow the fish.
