Divorce on a Rainy Day: How Extreme Weather Affects Social Behaviour in Wild Birds

Abstract

In the wild, most birds (ca. 90% of species) form strong bonds with a breeding partner, which are essential to raise offspring successfully. These bonds are not necessarily for life: sometimes pairs divorce. New research is showing alarming threats of climate change to the stability of avian partnerships. In this study on the Seychelles warbler ( Acrocephalus sechellensis ), a small bird endemic to a handful of islands in the Indian Ocean, we explored how rainfall variability influences divorce likelihood. Using 16 years of data on an entire population of individually marked birds, we measured who formed pair bonds with whom and when divorces happen. Using local monthly weather data, we found that divorce rates increase as a response to unusually dry and wet spells. As climate change increases the frequency of these extremes in local rainfall, the stability of pair bonds and the reproductive success of already vulnerable populations are at risk. This case introduces the importance of understanding social relationships in wild animals, how these relationships are modulated by environmental change, and how this affects the well-being of individual animals and entire populations.