If you missed last week’s Mating Monday on monogamy you can check it out here.
The more I study avian social behavior, the more I realize that humans and birds are not so different after all. Just like in human relationships, sometimes things don’t work out and birds decide to get divorced.
How common is divorce in birds? It’s estimated that divorce occurs in 95% of bird species. Ornithologists describe divorce as when a pair of socially mated birds choose to re-pair with different partners. This can happen after or during the breeding season. There are multiple reasons a bird may want to stay faithful to the same partner. Fidelity has benefits: it helps save energy since time doesn’t have to be wasted finding a new partner. Plus, a familiar pair bond increases cooperation and coordination when raising young. However, when things go wrong there are also many reason why divorce could make more sense than staying together.
It’s common for breeding attempts to fail. Therefore, a pair bond with poor success may find it more beneficial to seek new partners. Mercier et al. states that divorce could be considered an “adaptive mechanism” against having suboptimal partners (2021). A divorcee has the opportunity to find a better mate and possibly more breeding success. Infidelity can also be a reason for avian divorce. Promiscuity in males, but not in females, coincides with divorce rates.
Splitting up doesn’t always have to do with whether or not the nest failed. Sometimes the timing just isn’t right. A study of Eurasian Blue Tits found that 64% of the breeding pairs divorced before the experiment ended, even if the pair had a history of breeding success. Why? If both birds in a pair returned to the breeding territory around the same time they were more likely to stay together, but if the timing was off there was a higher chance of divorce. Since mortality rates are high for many birds, if a mate doesn’t show up “on time” they could be dead or injured. In cases like this fidelity may not pay off. Waiting around could mean losing the chance to breed, so finding a new partner is imperative. Also, studies have found that long-distance migrants such as Arctic Terns have higher divorce rate since unpredictable factors can affect whether or not they return to the breeding grounds on time.
Albatrosses have some of the lowest divorce rates in the avian world. Pairs usually stay together for decades in these long-lived species. However, divorce can still occur and there are some interesting reasons as to why. In Wandering Albatrosses personality can influence divorce. “Shy” males tend to avoid confrontation with bolder males who “intrude” in their territory seeking the female’s attention. As a result the shy bird may give up and desert the relationship. The shy birds were twice as likely to get divorced compared to the aggressive birds.
Environmental factors, such as climate change, may be influencing divorce rates in some albatross species. Ventura et al. studied 15,000 pairs of Black-browed Albatrosses that bred in the Falkland Islands over 15 years. The typical divorce rate of this species is between 1-3%, but in years with unusually warm water temperatures that percentage went as high as 8%. Warm water temperatures means having to travel farther to find food and can trigger stress hormones that leave birds with less energy to raise their chick. Ventura et al. refer to this as the partner-blaming hypothesis. These hormones can lead females to attribute the higher physiological stress to a poor performance by the male. By returning to the breeding grounds exhausted, stressed, and overworked the female may move on to a new partner.
Just for fun I wanted to wrap up this post with some divorce rates: 40-45% in humans, 9% in Mallards, 67% in Piping Plovers, 85% in Emperor Penguins, 99% in flamingos, and 100% in Great Blue Herons. And even swans, which the media likes to have us believe always mate for life, have a 5% divorce rate.
References
- Chen, Y., Lin, X., Song, Z., & Liu, Y. (2022). Divorce rate in birds increases with male promiscuity and migration distance. bioRxiv, 2022. doi: https://doi.org/10.1101/2022.10.13.512018
- Dunens, E. (2017, September 10). Albatrosses [Photograph]. Wikimedia Commons. https://commons.wikimedia.org/wiki/File:Albatrosses_(36336954984).jpg
- F&M. (2022). RESEARCH: Long distance travel for migrating birds has disadvantages-a high ‘divorce rate. Similar But Different in the Animal Kingdom. https://similarbutdifferentanimals.com/2022/11/18/research-long-distance-travel-for-migrating-birds-has-disadvantages-a-high-divorce-rate/
- Goldman, J. G. (2018). Why Do Birds Get Divorced?. Scientific American. https://www.scientificamerican.com/article/why-do-birds-get-divorced/
- Krulwich, R. (2014). Introducing A Divorce Rate For Birds, And Guess Which Bird Never, Ever Divorces?. NPR. https://www.npr.org/sections/krulwich/2014/04/22/305582368/introducing-a-divorce-rate-for-birds-and-guess-which-bird-never-ever-divorces
- Lubofsky, E. (2022). When it comes to albatross ‘divorce’, climate isn’t the only issue. Woods Hole Oceanographic Institute. https://www.whoi.edu/oceanus/feature/when-it-comes-to-albatross-divorce-climate-isnt-the-only-issue
- Mercier, G., Yoccoz, N. G., & Descamps, S. (2021). Influence of reproductive output on divorce rates in polar seabirds. Ecology and Evolution, 11(19), 12989-13000. doi: 10.1002/ece3.7775
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