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Great tits show early signs of splitting up, providing social clues to bird 'divorce'

In a discovery that deepens our understanding of animal social bonds, a study led by University of Oxford researchers in collaboration with the University of Leeds has demonstrated that wild great tits exhibit clear behaviors signaling "divorce" long before the breeding season. The findings, in Proceedings of the Royal Society B, provide valuable new insights into how animals navigate complex social decisions.

For monogamous birds that only bond with one partner at a time, choosing a mate has a critical bearing on reproductive success. Earlier studies have examined why some monogamous birds stay with the same partner while others "divorce" before the next breeding season. What remained unclear, however, was how their day-to-day social ties during the non-breeding season indicate a future split.

Finding the early clues of divorce would be highly challenging to explore for most bird populations. However, the new study leveraged data from the Wytham Woods great tit project, one of the most intensively studied wild bird populations in the world, which has run for over 75 years. This enabled the researchers to generate robust, quantitative data on the social interactions between individual birds.

Fascinatingly, the data showed that early signs of divorce could be identified in the winter, months before the couples rebreed with different partners in the following spring. This suggests that winter socializing during the non-breeding season is indicative of what will be seen in the following mating period.

Key findings:

• Winter behavior can predict springtime divorce. Pairs that later separated spent significantly less time together during the winter than those that remained faithful.
• Faithful pairs increasingly bonded over time, while divorcing pairs grew more distant—even visiting feeders at different times.
• Birds heading for a split rarely preferred to socialize with their breeding partner—unlike faithful birds, whose bond strengthened over time.

Lead researcher, Ph.D. candidate Adelaide Daisy Abraham (Department of Biology, University of Oxford), said, "Our results show that bird relationships are far from static. We found a clear behavioral signature in the winter months that can forecast a pair's likelihood of divorcing by spring. Divorce appears to be a socially driven process, unfolding over time."

To assess the birds' social associations, the researchers recorded how they behaved around feeding stations equipped with advanced RFID (Radio-Frequency Identification) technology. These feeders automatically detected tiny electronic tags carried by the birds in the study, recording their presence. This enabled the researchers to generate high-resolution datasets for each individual, mapping which birds they associated with at the feeders.

This data was compared with information on which birds had formed pairs together during the previous and following breeding seasons. The results clearly showed that faithful wild great tits visited the feeders with their breeding partners significantly more often than pairs that went on to divorce.

Professor Ben Sheldon (Department of Biology, University of Oxford), head of the Wytham study, noted, "This work is an important step towards uncovering the social mechanics behind pair bonding and fidelity in the wild. Our study has revealed that it is possible to use behavioral dynamics in wild animal pairs to predict future social states, such as divorce."

By following the same birds across multiple years, the study links how partnerships form, persist, and unravel through the seasons. This offers rare insight into the life cycle of social relationships in a wild, pair-bonding animal, and could now potentially guide future work in other species. Further, as the tell-tale signs of divorce are now identified, researchers can use this to investigate the causes and consequences of divorce as they unfold.

Senior author Dr. Josh Firth (University of Leeds) said, "Following these individual birds across seasons and over many years allows us to see how relationships form and break down in nature in a way that short-term studies wouldn't. Going forward, carrying out new experiments in the wild will provide even more opportunities to really understand the fine-scale dynamics of bonding and separation in natural settings."