As I wrote about earlier, many animals have intersex members, showing that the sex binary is not all that’s found in nature. It turns out, sex variation isn’t the only interesting thing found in nature; fluid sexuality is natural among animals too. New evidence shows that fluid sexuality is normal — and common — in the animal kingdom, at least among birds.

Sexually fluid behaviors have been examined in a study of hundreds of species of birds. Among the birds studied, the gender that spends less time raising babies is more likely to engage in homosexual behavior. In species where females raised hatchlings, male birds were more likely than female birds to engage in same-sex behavior, whereas species where both sexes raised babies included same-sex behaviors for both females and males.

The study found homosexual behavior in over 100 bird species, including relationships ranging from casual sex to joint child-rearing. In bird species that aren’t monogamous, homosexual behavior is more common. In fact, those birds with same-sex flings in non-monogamous species seemed to have as much reproductive success as those who didn’t engage in same-sex behavior.

Same-sex partnerships even benefited some birds, helping in raising young birds or to defend territories.

Birds are far from the only animal that engages in homosexual activities. Homosexuality has been documented in many animals, including cats, dogs, dolphins, chicken, and several species of fish.

Those opposed to LGBT equality often argue that heterosexuality is the only natural sexuality. But, as it turns out, science proves otherwise.

Photo credit: Mike Baird