Avian hybrids might be more common in the wild than previously believed, according to a new book, Handbook of Avian Hybrids of the World (Oxford University Press), by geneticist Eugene McCarthy, Ph.D., of the University of Georgia. “For many years, animal hybrids were believed to occur only rarely, and even then, primarily in captivity,” said McCarthy. “But avian hybrids cannot be so easily dismissed.” Hybrids occur “in virtually every country of the world,” he added.
The book runs 600 pages and lists all known and suspected hybrids (including captive-bred), where they are located and an assessment of fertility in hybrids. Two hundred and forty-seven parrot crosses are mentioned as well as 23 cockatoo crosses.
Hybrids are known for their sterility, but McCarthy found that many of them are in fact quite fertile and reproducing “in huge numbers.” Agapornis lovebirds and rosella hybrids are among those producing fertile hybrids. Unlike mammals, male hybrid birds are more likely to be fertile than females.
In captivity, hybrids can be avoided if differing species are kept separate. In the wild, whether or not a species interbreeds might have to do with its location or upbringing. McCarthy found that crossbreeds often live in “hybrid zones,” regions where hybrids are produced on an ongoing basis. These zones occur all over the world, he said. A lack of appropriate mates might have something to do with the behavior but so might early learning as a fledgling. McCarthy said that the song of a male overheard by a female nestling of another species might influence the adult female’s mate choice later on, as could the appearance of another bird.