Pelicans are very large birds with very long bills characterized by a downcurved hook at the end of the upper mandible, and the attachment of a huge gular pouch to the lower. The slender rami of the lower bill and the flexible tongue muscles form the pouch into a basket for catching fish, and sometimes rainwater, though not to hinder the swallowing of large fish, the tongue itself is tiny. They have a long neck and short stout legs with large, fully webbed feet. The tail is short and square. The wings are long and broad, suitably shaped for soaring and gliding flight, and have the unusually large number of 30 to 35 secondary flight feathers.
Males are generally larger than females and have longer bills.The smallest species is the brown pelican, small individuals of which can be no more than 2.75 kg (6.1 lb) and 1.06 m (3.5 ft) long, with a wingspan of as little as 1.83 m (6.0 ft). The largest is believed to be the Dalmatian, at up to 15 kg (33 lb) and 1.83 m (6.0 ft) in length, with a maximum wingspan of 3 m (9.8 ft). The Australian pelican's bill may grow up to 0.5 m (1.6 ft) long in large males, the longest of any bird.
Pelicans have mainly light-colored plumage, the exceptions being the brown and Peruvian pelicans. The bills, pouches, and bare facial skin of all species become brighter before breeding season commences. The plumage of immature pelicans is darker than that of adults. Newly hatched chicks are naked and pink, darkening to grey or black after 4 to 14 days, then developing a covering of white or grey down.
Modern pelicans are found on all continents except Antarctica. They primarily inhabit warm regions.
Pelicans swim well with their strong legs and their webbed feet. They rub the backs of their heads on their preen glands to pick up an oily secretion, which they transfer to their plumage to waterproof it.
Adult pelicans rely on visual displays and behavior to communicate, particularly using their wings and bills. Agonistic behavior consists of thrusting and snapping at opponents with their bills, or lifting and waving their wings in a threatening manner. Adult pelicans grunt when at the colony, but are generally silent elsewhere or outside breeding season. Conversely, colonies are noisy, as chicks vocalize extensively.
The diet of pelicans usually consists of fish, but occasionally amphibians, turtles, crustaceans, insects, birds, and mammals are also eaten. The size of the preferred prey fish varies depending on pelican species and location. In deep water, white pelicans often fish alone. Nearer the shore, several encircle schools of small fish or form a line to drive them into the shallows, beating their wings on the water surface and then scooping up the prey.
Although all pelican species may feed in groups or alone, the Dalmatian, pink-backed, and spot-billed pelicans are the only ones to prefer solitary feeding. When fishing in groups, all pelican species have been known to work together to catch their prey, and Dalmatian pelicans may even cooperate with great cormorants. They catch multiple small fish by expanding the throat pouch, which must be drained above the water surface before swallowing. This operation takes up to a minute, during which time other seabirds may steal the fish.
Food is not stored in a pelican's throat pouch, contrary to popular folklore.
Pelicans are gregarious and nest colonially. Pairs are monogamous for a single season, but the pair bond extends only to the nesting area.
The ground-nesting (white) species have a complex communal courtship involving a group of males chasing a single female in the air, on land, or in the water while pointing, gaping, and thrusting their bills at each other. They can finish the process in a day. The tree-nesting species have a simpler process in which perched males advertise for females.
The location of the breeding colony is constrained by the availability of an ample supply of fish to eat, although pelicans can use thermals to soar and commute for hundreds of kilometers daily to fetch food.
In all species, copulation takes place at the nest site; it begins shortly after pairing and continues for 3–10 days before egg-laying. The male brings the nesting material, in ground-nesting species (which may not build a nest) sometimes in the pouch, and in tree-nesting species crosswise in the bill. The female then heaps the material up to form a simple structure.
The eggs are oval, white, and coarsely textured. All species normally lay at least two eggs; the usual clutch size is one to three, rarely up to six. Both sexes incubate with the eggs on top of or below the feet; they may display when changing shifts. Incubation takes 30–36 days;hatching success for undisturbed pairs can be as high as 95%, but because of sibling competition or siblicide, in the wild, usually all but one nestling dies within the first few weeks (later in the pink-backed and spot-billed species). Both parents feed their young. Small chicks are fed by regurgitation; after about a week, they are able to put their heads into their parents' pouches and feed themselves. Sometimes before, but especially after being fed the pelican chick may seem to "throw a tantrum" by loudly vocalizing and dragging itself around in a circle by one wing and leg, striking its head on the ground or anything nearby and the tantrums sometimes end in what looks like a seizure that results in the chick falling briefly unconscious; the reason is not clearly known, but a common belief is that it is to draw attention to itself and away from any siblings who are waiting to be fed.
Parents of ground-nesting species sometimes drag older young around roughly by the head before feeding them.
From about 25 days old, the young of these species gather in "pods" or "crèches" of up to 100 birds in which parents recognize and feed only their own offspring. By 6–8 weeks they wander around, occasionally swimming, and may practice communal feeding.Young of all species fledge 10–12 weeks after hatching. They may remain with their parents afterwards, but are now seldom or never fed. They are mature at three or four years old.
Pelicans live for 15 to 25 years in the wild, although one reached an age of 54 years in captivity.