A new study says that birds that devote less time to their offspring engage in more same-sex behaviour.
The results of the study offer a possible explanation for the evolution of homosexuality: parents that devote less time to their offspring have more time and energy to interact with members of the same sex while still producing offspring.
Geoff MacFarlane, an ecologist at the University of Newcastle in Callaghan, Australia, and colleagues analysed records of 93 bird species that have exhibited homosexual behaviour in the wild, reports Nature.
They found that same-sex courtship, mounting and pair-bonding are prevalent: 38 percent of these species display female-female sexual behaviour and 82 percent participate in male-male behaviour.
In some species, nearly one-third of all sexual endeavours are female-female, and up to two-thirds are male-male. But overall, homosexual activity accounts for less than 5 percent of sexual encounters in the species they studied.
Bird species show a range of parental strategies, from male-dominated care to female-dominated care.
The team scored each species based on the relative contribution of males and females to parental chores, such as building nests, and feeding and defending chicks. Females that provide most of the care-taking show little to no homosexual behaviour.
By contrast, females that give less care show higher rates of same-sex courtship and pair bonding. Similarly, males that contribute less care exhibit more male-male courtship and pair bonding compared to males that devote more time to their offspring.
The authors suggest that a release from parental duties affords individuals a greater opportunity to interact sexually with multiple partners, including those of the same sex.
The study has been published this week in the journal Animal Behaviour.