With some ducks, the size of your male friends’ penises determines the size of yours. But what other crazy crap is going down with birds these days? Australian biologist Geoff MacFarlane found that among about 100 species of birds that exhibit same-sex behavior (read: from platonic courtships to genital touching), the most likely to engage in it are birds who don’t want to be around their kids.
In 2007, a team led by Geoff MacFarlane, a biologist at the University of Newcastle in Australia, reported that male homosexual behavior was more common in polygynous bird species, where males mate with numerous females, and that female homosexual behavior was more common in monogamous species. Intrigued, MacFarlane looked for help explaining the pattern in a theory predicting that whichever gender spends less time caring for young tends to have sex with more partners.
And what did he find?
To find out whether the theory might extend to homosexual behavior, MacFarlane and his team exhaustively combed the literature for accounts of same-sex courtship, mounting, or pair bonding. They focused on the 93 bird species whose homosexual interactions scientists had seen in the wild. For each species, the team calculated the frequency of homosexual behavior as well as both sexes’ contributions to parenting.
Overall, homosexual behavior amounted to less than 5 percent of all sexual activity in the 93 species, though in some cases it was much higher. And sure enough, there was a strong correlation between a species’ mating system and its homosexual behavior. Whichever sex did less parenting also typically did more same-sex canoodling – basically because they could. This tended to be true for the promiscuous males in polygynous species. The balance shifted to females in socially monogamous species, where the sexes split the work more equitably. So far, female homosexuality hasn’t turned up in the handful of birds where each female mates with many males, but MacFarlane’s team predicts it may.
And thus, concludes MacFarlane, if you’re a daddy bird whose parental responsibilities are negligible, you’ve got all the time in the world to flap your feathers at the fella in the nest next door.