They are chicken-like in appearance, with rounded bodies and blunt wings, and range in size from small at 15 cm (6 inches) to large at 120 cm (4 feet). They are mainly terrestrial birds and their wings are short and rounded for short-distance flight.
Plumage coloration ranges from cryptic to dark to brightly colorful. Some gallinaceous birds have elaborate head and neck ornamentation including feathers, wattles and casques.
Tail length is variable by species, from appearing almost tailless to long (1 m) with colorful and elaborate patterns. The legs are usually strong and one or more spurs may be present on the tarsus. Some species are sexually monomorphic in size and plumage coloration, while others are sexually dimorphic.
As a group, Galliformes has a nearly worldwide distribution.
Gallinaceous birds eat a variety of plant and animal material. Plant material includes: fruits, seeds, leaves, shoots, flowers, tubers and roots. Animal material includes: arthropods, snails, worms, lizards, snakes, small rodents, avian nestlings and eggs.
Gallinaceous birds may be either arboreal or terrestrial. Although some fly long distances, most move about mainly by walking and fly relatively infrequently. Many species roost in trees and are most active at dawn and dusk. Gallinaceous birds may be seen dust-bathing in open areas, usually in close proximity to scrub or other ready cover. Arboreal species forage mainly in trees, but may infrequently forage on the ground.
When startled or alarmed some gallinaceous birds fly straight up into the air, then fly horizontally away from the source of the disturbance. Some species are solitary while others spend some part of the year in mated pairs or in flocks. Dominance hierarchies are evident in some species that live in social groups.
Gallinaceous birds exhibit a diversity of mating systems including monogamy, polygyny and polygynandry. Pair bonds, if evident, may last only through copulation or may persist over multiple breeding seasons. Courtship behaviors may entail elaborate displays of brightly colored skin and plumage. In some species dominance hierarchies exist, and high-ranking males often have greater mating success than lower ranking males.
Most species breed seasonally in relation to local climactic conditions. Gallinaceous birds may nest on the ground or in trees. In some species nests are shallow, and lined with grass or leaves. Megapodes construct incubation mounds in which eggs are incubated environmentally, through the heat generated by decomposing vegetation, sun-warmed sand or geothermal sources.
Females may lay from 2 to 35 eggs over the course of the breeding season. Egg coloration varies, from white or creamy to brown or spotted. Chicks are precocial, able to walk, forage and fly shortly after hatching.
In gallinaceous birds parental care may include female incubation or environmental incubation (incubation mounds of megapodes). Brooding may be absent, or conducted primarily by the female. Males may guard nest sites, brooding females, or chicks.
In some gallinaceous birds, parents do not feed their young while in others the female provisions chicks with food offered from her bill. Family groups may join flocks at the end of the breeding season.
These birds live 5–8 years in the wild and up to 30 years in captivity.