Chickadees, the birds that divorce and give signs of the breakup months in advance: they don't want to even see each other.

Great tits are small, monogamous birds that only bond with one partner at a time. Some pairs remain together over the seasons, but others divorce before the next breeding season. Researchers from Oxford and Leeds University in Britain have studied the behavior of these birds, common in Europe and Asia, and have found clear clues that indicate an impending separation. A very clear "friend, notice!" with feathers. The findings, published in the Proceedings of the Royal Society B, provide valuable insight into how animals navigate complex social decisions.

The researchers collected the data for their study from the Wytham Woods Great Tit Project, one of the most extensively studied wild bird populations in the world, with over 75 years of experience, near Oxford. Interestingly, the data showed that the first "divorce signals" could be identified in winter, months before the birds bred with different partners the following spring.

For example, pairs that subsequently separated spent much less time together during the winter than those that remained faithful. Faithful pairs bonded more and more over time, while divorced pairs became more distant, even visiting feeders at different times. Rather like eating dinner at different times so as not to share time at the feeding station. Furthermore, birds preparing to separate rarely prefer to socialize with their breeding partner, unlike faithful birds, whose bond strengthens over time.

Adelaide Daisy Abraham, the study's lead researcher from Oxford's Department of Biology, is clear: "Our results demonstrate that relationships between birds are far from static. We found a clear behavioral signal in the winter months that can predict a pair's likelihood of divorce by spring. Divorce appears to be a social process that develops over time."

To assess the birds' social associations, researchers recorded their behavior around feeders equipped with advanced radio-frequency identification (RFID) technology. These feeders automatically detect tiny electronic tags worn by the study birds, recording their presence. This allowed the researchers to generate individual-specific data sets, mapping which birds they associated with at the feeders.

These data were compared with information on which birds had formed pairs during the previous and subsequent breeding seasons. The results clearly showed that faithful great tits visited feeders with their breeding partners much more frequently than those pairs that had divorced.

"This work represents an important step in uncovering the social mechanisms underlying pair bonding and fidelity in the wild. Our study has revealed that behavioral dynamics in wild animal pairs can be used to predict future social states, such as divorce," says Ben Sheldon, also from the Department of Biology and leader of the Wytham study.

By following the same birds over several years, the study links how pairs form, persist, and dissolve across seasons. This offers exceptional insight into the life cycle of social relationships in a pair-forming wild animal and could inform future research with other species. Furthermore, by identifying the telltale signs of divorce, researchers can use this information to investigate the causes and consequences of such separations as they unfold.

Human behavior is far more sophisticated than that of a small bird and is influenced by thousands of factors that don't occur on tree branches and at bird feeders, but it will be difficult for many to avoid the temptation to compare these birds' relationship patterns with the state of their marriage... and draw conclusions.