Rumpless

Rumpless refers to a genetic mutation found in certain breeds of chickens that results in the absence of a tail or rump. This mutation is a naturally occurring one and is not considered detrimental to the bird's health or well-being. Chickens with this trait typically have a reduced or absent uropygial gland, also known as the preen gland, which is responsible for secreting oil that birds use to waterproof and condition their feathers.

The most well-known breed exhibiting this trait is the Araucana chicken, which also possesses other distinctive characteristics such as ear tufts and blue-shelled eggs. However, rumplessness can appear in other breeds as well, often as a result of crossbreeding or selective breeding for this particular characteristic. The genetic basis for rumplessness is understood to be an autosomal gene, meaning it is not linked to the sex chromosomes.

While the absence of a tail might seem unusual, rumpless chickens function normally. They can fly, forage, and reproduce just like their tailed counterparts. In some breeding programs, the rumpless trait is selectively bred for its aesthetic appeal or to create distinct breed lines. The genetics of tail development in birds are complex, and the rumpless mutation represents a variation in this developmental pathway.