Same-Sex Parenting Can Be an Adaptive Advantage

Same-sex bird couples produced fewer offspring than traditional couples, but they still reared more chicks than solo parents

Hjalmar Gislason

Same-sex human parents are commonplace these days, but we are not the only species that sometimes pursue this particular parenting arrangement. In an albatross colony in Oahu, Hawaii, for example, around 30 percent of couples that come together to raise a chick are two unrelated females. The females may continue to pair with one another for years. In this case, they alternate every other year who gets to lay the egg, fertilized by one of the males in the colony that already has a female mate.

Researchers decided to investigate and find out whether those females are at any disadvantage compared to their traditional peers. They monitored the colony from 2003 to 2012, recording who mated with whom, how many eggs were laid and whether those chicks hatched and survived to fledge the nest.

Over those ten years, they report in the journal Proceedings of the Royal Society B, same-sex pairs raised fewer chicks on average compared to male-female couples, and individual females in those same-sex couple produced fewer of their own offspring than females that paired with males. However, those same-sex pairs still produced more offspring than birds that had no partner at all.

In this particular colony, the females are likely pairing with each other because of a sex ratio skew (60 percent of the birds are female), and so rather than skip breeding all together, the researchers write, they may be “‘making the best of a bad job’ in response to a shortage of males,” the authors write. In other words, under the circumstances, same-sex pairings are an adaptive advantage for certain females.

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