The male of this huge bird is possibly the heaviest living flying animal, reaching up to one metre tall and weighing up to 16kg. The great bustard (Otis tarda) is in the bustard family, the only member of the genus Otis. It breeds in southern and central Europe, where it is the largest species of bird, and across temperate Asia. The species became extinct in the UK in 1832, but is on its way back thanks to the work of the Great Bustard Group. An adult male is brown above and white below, with a long grey neck and head. The breast and lower neck sides are chestnut. In the breeding season, the male has long white neck bristles. In flight, the long wings show large areas of white. Male Great Bustards grow about 30% larger than the females – there is a marked difference in size between males and females, termed sexual size dimorphism. Great Bustards actually exhibit the largest sexual size dimorphism of any bird species and most other mammals, birds, reptiles, amphibians, and fish! Female Great Bustards can be as much as 50% smaller than males.and can be identified by their bulging neck, heavy chest and characteristically cocked tail. Shape is similar to a large goose, but the bustard is much larger with considerably longer legs and a straighter neck. The head and neck are a pale blue-grey, the body and tail rufous brown with black bars, and underparts white. The wings of the Great Bustard are mostly white with dark primary and secondary feathers.