The Great bustard (Otis tarda) is a bird in the bustard family, the only member of the genus Otis. It is one of the heaviest birds alive today that can fly. Great bustards are found in Europe and Portugal and Spain now have about 60% of the world's population. This species became extinct in Great Britain when the last bird was shot in 1832. Recent attempts to reintroduce it into England have met with some success and there is a population of 40 birds on Salisbury Plain, a British Army training area. Here the lack of public access allows them the freedom needed as a large ground-nesting bird.
An adult male Great bustard is brown above, barred with blackish colouration, and white below, with a long grey neck and head. His breast and lower neck sides are chestnut and there is a golden wash to the back and the extent of these bright colours tends to increase as the male ages. In the breeding season, the male has long white neck bristles, which measure up to 12-15 cm (4.7-5.9 in) in length, continually growing from the third to the sixth year of life. In flight, the long wings are predominantly white with brown showing along the edges of the lower primary and secondary feathers and a dark brown streak along the upper-edge of the wing. The breast and neck of the female are buff, with brown and pale colouration over the rest of the plumage rendering it well camouflaged in open habitats. Immature birds resemble the female. The eastern subspecies (O. t. dybowskii) is more extensively grey in colour in both sexes, with more extensive barring on the back. The Great bustard has long legs, a long neck and a heavy, barrel-chested body. It is fairly typical of the family in its overall shape and habitat preferences.
Great bustards are endemic to central and southern Europe, where they are the largest bird species, and across temperate Asia. In Europe, populations are mainly resident, while Asian birds travel further south in winter. These birds inhabit grasslands, steppe and forest steppe, defined by open, flat, or somewhat rolling landscapes. They can be found on undisturbed cultivation and prefer areas with wild or cultivated crops such as cereals, vineyards, and fodder plants. However, during the breeding season, they actively avoid areas with regular human activity and can be disturbed by agricultural practices. When nesting, they favor areas with little or no presence by humans.
Great bustards are diurnal birds. Since males and females of this species differ in size, for this reason, they live in separate groups for almost the whole year, except during the mating season. This size difference also affects food requirements as well as breeding, dispersal, and migratory behaviors. Females usually flock together with individuals who are related. They are more philopatric and gregarious than males, and will often remain in their natal area for their entire life. In winter, males establish a group hierarchy, engaging in violent, prolonged fights, stabbing the head and neck of other males, sometimes causing serious injury, behavior which is typical of bustards. Great bustards have a stately slow walk but tend to run when disturbed rather than fly. Running speeds have not been measured but adult females have been known to outrun Red foxes, which can reach a trotting speed of 48 km/h (30 mph). These birds are also strong fliers and reach speeds of 48 km/h (30 mph) to 98 km/h (60 miles/hr) during migration. Those populations of Great bustards that are migratory gather at pre-migratory sites in great numbers in order to collectively move to winter grounds. These birds are usually silent but may make deep grunts when angered or alarmed. An adult male when displaying may produce booming, grunting, and raucous sounds. Females may make some guttural calls when at the nest, while brooded young when communicating with their mothers make a soft, trilling call.
The Great bustard is omnivorous, it eats vegetation such as grass, legumes, crucifers, grains, flowers, and grapes. It also eats rodents, the chicks of other species, earthworms, butterflies, large insects, and larvae. Lizards and amphibians are also eaten, depending on the season.
Great bustards are polygynous, and one male may mate with as many as five females. The males perform spectacular courtship displays, competing in a lekking system, where they gather at a ‘lek’ or small display ground to try to impress the females. The breeding season is in March, and eggs are laid in May-June, depending on the region. Nests are usually close to leks. 2-3 eggs are laid and the female on her own incubates them for about 25 days to a month. Chicks are precocial and can immediately leave the nest. Their mother raises them and they fledge at around 30-35 days. They do not reach full size until 80 to 120 days old, and for about ten months are dependent on their mother.
This species suffers from the fragmentation and loss of its habitat. Increasing land privatization and human disturbance are expected to cause more habitat loss with the plowing of grasslands, afforestation, intensive agriculture, increased use of irrigation schemes, and construction of power lines, roads, fencing, and ditches. Chemical fertilizers and pesticides, mechanization, fire, and predation are major threats for the chicks and juveniles, while hunting of adult birds causes high mortality in some countries where they live.
According to the IUCN Red List, the total population size of the Great bustard is around 44,000-57,000 individuals. Currently, this species is classified as Vulnerable (VU) and its numbers today are decreasing.