Hornbills generally groom their feathers as their first activity after dawn, and then begin searching for food. They move in pairs, but some species move in family groups of three to twenty. When plenty of food is available, larger groups may come together. Bills are used for various functions including feeding, grooming, and nest-sealing. They are not considered as migratory birds, but are territorial for many species.
Hornbills display sounds that are described as the noise made by an approaching train. The sound is possible because hornbills do not have small feathers that cover their flight feathers; so wings allow air to pass through, producing train-like vibration sounds. These "whooshing" sounds come in different intensities depending on wing size, and are used to defend the territory and to maintain contact with group members.
Hornbills are believed to be monogamous (muh-NAH-guh-mus), having only one mate. Usually one breeding pair will be joined by earlier offspring who help raise the latest brood. Courtship begins when pairs fly together through the air, perch close to each other, groom one another, and exchange food.
Hornbills use an interesting nesting pattern. They build nests in holes, mostly natural cavities, hollow areas, in trees or rock crevices. However, unlike most other birds, all hornbills, except a few, seal the cavity entrance, leaving only a slit through which the female, and later her young, receive food from the male. The male brings mud to the female who use it, along with her saliva, to seal the opening. If mud is not available, the female will substitute her own feces, solid waste. Egg size and number, and incubation period, the time needed to sit and hatch the eggs, depends on female body size. Clutch size, number of eggs hatched together, ranges from two to three eggs in large hornbills, and up to eight for smaller hornbills. Incubation periods run between twenty-three and forty-nine days. Eggs hatch in intervals, with the chicks emerging naked, pink, and blind. Feather growth begins in a few days, with the skin turning black. Fledglings, young who have grown enough feathers to be able to fly, have underdeveloped casques and small bills, but after about one year, their appearance is like the adults.
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