Pelecaniform birds (pelicans, ibis, herons, and spoonbills) usually nest in groups on islands or other isolated places. Colonies can number in the thousands, making for crowded nesting areas. Pelecaniforms tend to live a long time, and some return to the same nesting sites year after year. Individuals may even pair with the same mate again. Using twigs, aquatic plants, or other materials gathered by the male, the female builds a nest, sometimes just a few inches from nests of other females. The parents take turns incubating the eggs. They transfer heat from their bodies by wrapping their four webbed toes around the eggs. Pelecaniform chicks are typically born helpless and naked, and take a long time to mature (seven months in some species). Both parents care for them, feeding them with regurgitated fish and other food. Even after the chicks can fly, parents continue to provide food while the chicks learn hunting skills.

All modern birds have bills and no teeth. The shape of a bird's bill says a lot about what it eats, for example whether it specializes in seeds (stout , cracking bill), fish (pointy, spearing bill), or plants (wide, serrated bill). Birds swallow their food without chewing, so it travels to the stomach whole or in large pieces. Bird digestive tracts have some special features for digesting chunky food. A pouch in their throat (the crop), is used to store food to be digested later, or regurgitated to feed the young. An extra, muscular stomach (the gizzard) grinds food up. Birds are endotherms, using heat they make internally to keep warm. While a few species allow their body temperature to drop at night (torpor), a nearly constant body temperature is maintained by most birds most of the time. Continuously making heat requires fuel to burn, in the form of food. So, birds spend a lot of time eating.