Kroot are large, lanky humanoids descended from avian ancestors. They have grey skin and dark quills and beaks, are well adapted to living in forests, and have very efficient metabolisms. Kroot are very strong and quick creatures. Kroot are carnivorous and quite willing to eat the corpses of defeated foes.
Kroot have the notable ability to absorb DNA from creatures that they have eaten. This allows Kroot to acquire useful characteristics from fallen enemies, such as the technological instincts of Ork Mekboys, the strength of Orks or the agility of Eldar. DNA acquisition can sometimes have unfortunate side effects, however, as several strains of Kroot lost sapience and degenerated into bestial forms such as Kroothounds and Krootoxen. Greater risks still come from consuming the flesh of Tyranids or that of those corrupted by Chaos, which can cause Kroot to become slaves to the Tyranid Hive Mind or succumb to the corruption by the Ruinous Powers themselves.
Kroot society is divided into loose clans known as Kindreds, lead by figures known as Shapers. Shapers decide what genetic material their Kindreds may ingest to "evolve" and develop particular traits. A few strains of degenerated, non-sapient Kroot have been domesticated and are used as warbeasts in battle.
The Kroot have colonized a few worlds along the fringe of the Tau Empire. Kroot prefer to live in tropical rainforests and -- outside of subterranean industrial complexes on their homeworld of Pech and the use of their spacecraft known as Warspheres -- tend to live rather primitive lives.
As part of the Tau Empire, the Kroot provide auxiliaries to fight alongside Fire Caste Forces. This (among other things) allows them to go up against a multitude of foreign species from which to acquire new genetic material. Kroot are skilled close combat fighters, generally armed with bladed rifles, and are useful for the Tau for making up for the natural disadvantages the Tau have in hand-to-hand combat.