Skewed sex ratios induce same-sex behaviour in pigeons

Numerous records of such bonding exist in nature

Pairing: One of the pigeon pairs observed for the study in the breeding colony in Poland.

It’s all about making the best of a bad job: if there is a paucity of males, female rock pigeons can form long-lasting, same-sex relationships to bring up their chicks, find scientists. Such female pairs fare no differently than female–male pairs, and better than single females, in bringing up their brood.

Numerous records of same-sex sexual behaviour exist in the natural world and more than 130 bird species have been recorded displaying such behaviour, ranging from courtship displays and copulation to establishing nesting territories. Theories put forward to explain this include ‘social glue’ (where engaging in same-sex bonds establishes strong social relationships), ‘alloparenting’ (that females have a fluid sexuality that helps them form same-sex bonds if their partners die or leave, which is useful to bring up offspring) and the ‘prison effect’ (removing one sex causes the rest to engage sexually with members of its own sex).

A team of scientists from Poland tested what would happen if males or females are removed from populations of rock (feral) pigeons, a monogamous species (which has only one mate at a time) that is also found in India.

In their study published in

Scientific Reports, the scientists detail how they established three feral pigeon colonies between 2007 and 2009. From the first colony, they removed several males that had already paired with females. This skewed the sex ratio towards females, creating not just the existing female–male (f–m) pairs but also five female–female (f–f) pairs and 14 single females. Males from the f–m pairs fertilised the single females and those in the f–f pairs.

The team found that egg incubation time, development of chicks and numbers of hatchlings of f–f pairs was almost the same as f–m pairs, while single females did not do as well.

The removal of females from the second colony created only two short and unstable male–male pairs, which did not build nests or adopt offered eggs. From the third colony, when the team removed females whose fledglings were growing, males displayed mating behaviour towards their offspring.

“Our results show that a shortage of males evokes same-sex sexual behaviour in females in an effort to adapt and compensate for the lack of males,” writes lead author Łukasz Jankowiak (University of Szczecin) in an e-mail to The Hindu. According to Jankowiak, both alloparenting in females and prison effects in both females and males explain same-sex sexual behaviour in this case.