Understanding why birds stay together or part ways can reveal fascinating insights into how evolution shapes this behaviour.
Stay or split? Frigg Speelman is a researcher in behavioural ecology at Macquarie University who studies pair-bonds in birds.
While undertaking my PhD at Macquarie University, I worked with scientists from the Netherlands, UK and Seychelles on research published in Ecology Letters to explore this phenomenon further.
For many bird species, staying with the same partner can lead to better breeding outcomes. Familiarity and teamwork in raising chicks can make a big difference. However, switching partners can also offer benefits, such as finding a higher-quality mate or a better nesting spot, which can enhance the chances of survival and successful reproduction.
Divorce among birds is surprisingly common, occurring in over 90 per cent of socially monogamous species. Studies have shown that in some cases, this separation can lead to better breeding success and longer lifespans. Researchers are keen to understand the reasons behind these break-ups and their impact on the birds' lives.
We used data from a 24-year study of Seychelles warblers (Acrocephalus sechellensis), a small, socially-monogamous island songbird, to shed light on this phenomenon.
These birds, which can live up to 19 years but have an average lifespan of 5.5 years, are particularly interesting because they have virtually no migration and can be easily tracked throughout their lives. This allows scientists to gather detailed data on their partnerships and breeding success.
Risky business
The study found that divorce in Seychelles warblers is influenced by factors like previous reproductive output, the length of the relationship, and the age of the male. Specifically, pairs that produced fewer eggs were more likely to divorce in the following breeding season.
Both younger and older males were more likely to divorce than middle-aged males, with the lowest divorce rate in male birds around six to seven years old. Interestingly, females that lose their breeding position after a break-up have lower survival rates, suggesting that divorce might have some costs.
However, in general, divorce in Seychelles warblers is less common than in other species with only 14 per cent of partnerships ending in divorce compared to 69 per cent ending due to widowhood. We think this is likely due to intense competition for breeding spots.
For those interested in the romantic lives of birds, this research highlights the complexities of avian relationships. It suggests that while divorce can sometimes lead to better opportunities, it also carries risks.
The study found no evidence of short-term fitness benefits from divorcing, and the long-term consequences appear to be mainly negative for females who lose their breeding position.
Our research shows the love lives of birds are more intricate than we might have imagined.
By studying these patterns, scientists hope to gain deeper insights into the adaptive strategies birds use to survive and thrive in their natural habitats.
Future research will continue to explore whether divorce is a strategic move for birds' survival – or just a consequence of challenging circumstances.
Causes and consequences of divorce in a long-lived socially monogamous bird was published in Ecology Letters in December 2024 by lead author Macquarie University's Dr Frigg Speelman, in collaboration with T Burke, J Komdeur, D Richardson and H Dugdale.
Frigg Speelman is a behavioural ecologist in the Faculty of Science and Engineering, Macquarie University.
