Today I learned that some chickens (1 in 10,000 apparently) are born with ‘one half of them male, and the other half female,’ like the one above (who belongs to Redcatcher on BackyardChickens, as well as the pictures). They almost look like harlequin rabbits or tortoiseshell cats (or ‘chimeras’). They tend to only have one sex’s reproductive organs though.
They’re called Gynandromorph Chickens and they have a mixture of genetically male and female cells. I believe it is still unknown as to why exactly this happens, though it is said to happen because the egg is fertilized by two sperm.
They’ll most often show signs of being a rooster on one side- large waddles, saddle feathers, rooster coloring (if the sex of the chicken is determined by color, sometimes Gynandromorphism goes unnoticed because of this!), and the development of spurs, while the other side will have female features (lack of the before mentioned usually). It can actually happen in all birds (and other animals and insects as well), but is often not noticeable due to the sexes having such similar appearances. [x]