Bustards are all fairly large with the two largest
species, the
kori bustard (
Ardeotis kori) and the
great bustard (
Otis tarda), being frequently cited as the world's heaviest flying birds. In both the largest species, large males exceed a weight of , weigh around on average and can attain a total length of . The smallest species is the
little brown bustard (
Eupodotis humilis), which is around long and weighs around on average. In most bustards, males are substantially larger than females, often about 30% longer and sometimes more than twice the weight. They are among the most
sexually dimorphic groups of birds. In only the
floricans is the sexual dimorphism the reverse, with the adult female being slightly larger and heavier than the male. The wings have 10 primaries and 16–24 secondary feathers. There are 18–20 feathers in the tail. The plumage is predominantly cryptic. == Behaviour and ecology ==