Oxford Researchers Study Divorce Patterns in Great Tits

Why do birds divorce? Oxford University researchers have been studying great tits to find the answer to this question and determine what makes them decide to end a relationship. Most birds are socially monogamous but they will cheat on partners or separate to mate with another bird. The researchers found that with great tits divorce comes down to their social network and territory change.

The Oxford researchers have been observing a breeding population of great tits at Wytham Woods. These birds have been included in a large-scale study to understand their social behavior since 2007. Over 80 percent of the great tits that spend the winter in the woods are tagged with passive integrated transponders (PITs). Feeders in the woods are equipped with a PIT-detecting antennae and the date and time is recorded each time a bird lands on one of these feeders. The scientists are able to identify with birds socialize with each other and ascertain the strength of associations between pairs of birds. The Oxford research team analyzed the data of 6,743,553 feeder visits made by 3,198 different great tits between 2007 and 2014.

Dr. Antica Culina, the leader of the research team from the Department of Zoology, says in a statement, "Our feeders are opened once a week for two days, and in this way we can capture a snapshot of the social network among all the birds. By performing the same procedure many times over winter, we can track how relationships and social networks change over time."

The researchers found that male birds with a high proportion of female acquaintances are less likely to divorce their partner between breeding seasons. They also found males are less likely to divorce if the strength of the association with their partner is higher than their association with other females, and if they are experienced breeders.

Dr. Culina says, "Our results seems to suggest that males use divorce to correct for non-preferred partnership. They might not be able to breed with their preferred female, so they ended up simply breeding with a less preferred one — then in the next season, they move on to another partner."

The research team found that a female's social environment had no influence on the probability of divorce. This could be because males hold the territory in great tit bird populations. If a female bird decides to leave her mate for another she will likely be changing territory.

Dr. Culina says, "In great tits, males hold territories. That means that females that divorce their males also change territory. We wonder if females might pay more attention to the territory they want to live in than the social dynamics of the group when it comes to changing partners."

A research paper on the findings was published here in the journal, Proceedings of the Royal Society B. The paper is called, "Carry-over effects of the social environment on future divorce probability in a wild bird population."

More information about the study of the great tits population at Whytham Woods can be found on the Twitter account, @wythamtits.

Photo: Oxford University

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