鸟类同性恋

据澳大利亚纽卡斯尔大学的生物学家在2007年时研究表示，在“一夫多妻“的鸟种中雄性鸟同性恋的居多，在“一夫一妻”的鸟种中雌性鸟“同性恋”居多。同性恋，并且出现很多对长相厮守的同性鸟“夫妻”。

Nearly one-fifth of all long-term greylag geese couples are gay, composed of two males. Credit: Dreamstime. 将近1/5的灰雁“夫妻”是女同性恋，图为两只灰雁mm。灰雁这种神奇鸟类的猛料，请看鸟类网magggot的文章：《灰雁的早孕/SM/同性恋/3P/NP行为》）交配繁殖。最新研究显示，有一些特殊的鸟类可以在固定的周期内与同性和异性交配。通常，“同性恋”鸟类会向爱慕者发出精心准备的求爱“招术’，如果它们都互相爱慕就会相互碰触生殖器官，这也就表示新的一个同性家庭成立了。一些“同性恋”鸟类甚至会生幼崽，而且会相亲相爱的相守几年的幸福时光。交配，它们的异性“伴侣”会负责抚养幼崽。据估计，在这93种鸟类中至少有5%的鸟类有着同性交配行为。科学家表示，这些鸟类的同性恋行为多和交配系统有着很大的关系。英文原文：从进化角度解释鸟类同性恋存在的合理性

In greylag geese, nearly a fifth of all long-term couples are composed of two males. They're not alone: More than 130 bird species are known to engage in homosexual behavior at least occasionally, a fact that has puzzled scientists.

Birds engage in all kinds of same-sex hanky panky, from elaborate courtship displays to mounting and genital contact to setting up house together. In some species the same-sex pairs even raise young (conceived with outside partners, obviously) and stay together for several years.

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.

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.

Evolutionary outcomes

And with plenty of reproductive prospects, a little homosexual behavior won't have much effect on long-term reproductive success, MacFarlane said. "That's quite different to what the traditional argument is in the literature, where homosexual behavior is seen as a cost."

MacFarlane's team is now investigating whether primates exhibit patterns like the one they've found in birds.