Birb

Birbs are parrots that can be bred. Each birb carries two colour alleles, and breeding passes one allele at random from each parent, so offspring colour follows ordinary Mendelian inheritance rather than a fixed table. Birbs will replace vanilla parrot spawning.

There are five base colours: red, cyan, blue, green and gray. A birb carrying two matching alleles is pure and shows that colour; one carrying two different alleles is a hybrid and has its own appearance. Five pure colours and ten hybrid combinations give fifteen variants in total.

Allele pairs are order independent: a red-and-blue birb and a blue-and-red birb are the same variant.

Breeding

Breeding two tamed birbs produces a chick that inherits one allele from each parent, chosen at random. Crossing two pure birbs of different colours always gives a hybrid; crossing hybrids can restore a pure colour where both parents share an allele.

For example, crossing a red-and-blue birb with a green-and-blue birb gives four equally likely outcomes: red-and-green, red-and-blue, blue-and-green, and pure blue. The shared blue allele is the only one that can appear pure.

About 1% of birbs are born special, with a distinct appearance shared by all specials regardless of colour. This is appearance only: a special birb breeds exactly as its colours dictate, and the trait is not inherited. Every birth and wild spawn rolls independently.