Crossing birds of different species.

Reproduction with another species can and often does occur. A cross between two species is called "hybridization". However, it usually occurs with birds of the same genus.

The most common example of this is the Catalina macaw, which is a cross between a blue macaw and a red macaw; They are two different species, but of the same genus. It is possible for birds of different genera to produce offspring, but it is very rare and occurs mainly in loris, parakeets and some other parrots.

In the case of a parakeet, which is an Old World African parrot, and a conure, which is a New World South American parrot, it is impossible for the eggs to be fertile.