Extramarital affairs or longer separations often mean divorce for human couples. But apparently not just between humans: Similar factors play a role in separations between birds, new research shows.
It is believed that over 90% of bird species typically have a single mate for at least one breeding season, if not longer. However, some monogamous birds will switch to a different mate for a later breeding season even though their original mate is still alive — a behavior known as “divorce.”
While several studies have looked at possible factors related to these separations, experts say they tend to focus on individual species or groups of species. According to the Guardian, researchers now say they have found two main factors at play in divorce across a wide range of bird species: male promiscuity and longdistance migration.
Researchers in China and Germany describe in the journal Proceedings of the Royal Society B how they drew on analysis of previously published data on divorce rates for 232 bird species with mortality dates and migration distances. The team also gave the males and females of each species a separate “promiscuity score” based on published information about the birds’ behavior.
They also performed an analysis based on evolutionary relationships between species to explain the effects of common ancestry. The results show that species with remarkably high divorce rates tend to be closely related, a finding that also applies to species with remarkably low divorce rates. A similar pattern was observed for male promiscuity.
While the researchers found that greater promiscuity in men was associated with higher rates of divorce, this was not the case for promiscuity in women.
The team also found that species with longer migration distances had higher rates of divorce. “After migration, pairs may arrive at their destination asynchronously, allowing the early arrivals to mate with another mate, resulting in ‘divorce.'” Migration can also result in pairs ending up in different breeding grounds and there is a “divorce” due to an accidental loss. “This effect increases with increasing migration distance,” wrote the team, who found that longer migrations narrowed the window for reproduction.
The researchers also found that mortality rates and migratory distance appeared to be related to male promiscuity, suggesting possible knockon effects on divorce. The team says the results suggest that divorce in birds may not just be a strategy to increase an individual’s fitness or a response to ecological factors such as migration, but may be influenced by both simultaneously.