Bad weather causes more frequent “divorces” among waterbirds

Shorter days, cold rain, strong wind. Unfavorable weather makes relationships fall apart. Partners drift away from each other, and by the next season the bond is not renewed. It may sound like a story from the human world, but it concerns… waterbirds. A new study shows that strong winds do not favor monogamy. This is not just a curiosity but a sign of how changing climatic conditions affect the behavior of marine species.

Decline in fidelity among waterbirds

Scientists from Edinburgh Napier University, the UK Centre for Ecology & Hydrology (UKCEH), and Biomathematics and Statistics Scotland (BioSS) analyzed the impact of weather conditions on the faithfulness of bird pairs. The results were published in Animal Behavior. The team presented data collected over 20 years from more than 1,500 European shags (Phalacrocorax aristotelis) – a species considered monogamous and known to form long-term pair bonds across multiple breeding seasons.

It turned out that the level of fidelity among the birds varied greatly. On average, about 45 percent of shags reunited with the same partner in the following breeding season, but depending on the weather, this rate ranged from 25 to 72 percent. Researchers note that the average fidelity in this species is lower than in other monogamous seabirds.

The most important factor influencing pair reformation was wind strength before the breeding season. During windier periods, the birds were more likely to change partners.

Monogamy supports offspring

Reproductive success does not directly depend on whether the pair is new or previously bonded. However, bird fidelity affects the timing of breeding. Long-term pairs tend to lay eggs earlier, which increases chick survival due to better feeding conditions.

Although weather influences the stability of bird pairs, the study indicates that individual traits such as age, condition, and past breeding success still play a greater role. However, scientists emphasize that with the intensification of climate change, these proportions may shift. Warmer waters and stronger, more frequent winds are already beginning to affect bird behavior, reducing the stability of established patterns.

Higher water temperatures mean fewer chicks

Authors of another study on waterbirds, published in October 2025 in Communications Earth & Environment, point to an additional environmental factor. Changes in ocean water temperature –especially in the mixed layer – and differences in water density structure affect seabird reproduction. The analysis covered 138 breeding cycles of 39 species living in the Northern Hemisphere.

In most of the studied areas, researchers observed a correlation between pre-breeding water temperature and reproductive success. Higher temperatures led to a decline in the availability of plankton and other organisms that serve as natural food sources. The birds were not starving, but their diet became less diverse, reducing the intake of nutrients essential for reproduction. The steepest drop in breeding productivity was recorded in colder marine regions: the Arctic, northern European seas, and the northwestern Atlantic.

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Bibliography:

Sue Lewis, Adam Butler, Sarah Wanless, Mark A. Newell, Michael P. Harris, Sarah J. Burthe, Carrie M. Gunn, Richard J. Howells, Francis Daunt, Effects of environmental conditions on mate fidelity in a socially monogamous seabird, Animal Behaviour, 2025, 123356,ISSN 0003-3472, https://doi.org/10.1016/j.anbehav.2025.123356

Killeen, H., Sydeman, W.J., Hoover, B. et al. Ecosystems mediate climate impacts on northern hemisphere seabirds. Commun Earth Environ 6, 804 (2025). https://doi.org/10.1038/s43247-025-02717-z