Homosexual behaviour in animals is common, has been observed in over 1500 species and well documented in around 500. It's estimated that around 25% of mallard duck pairings are male-male (and incidentally, there is even a case of homosexual necrophilia recorded in mallards). It's not just sex either, standard pairing behaviour is present too.
I think this is a different case though, this is a chicken that for whatever reason (presumably hormonal) is showing male characteristics. Interesting stuff!