When climate conditions become more variable, birds are more likely to ‘cheat on’ and ‘divorce’ their mates. The hypothesized reason is that birds may be seeking out a greater diversity in genes for their offspring. An unstable climate could be deadly for birds, so breeding with a wider range of mates could increase the likelihood that their offspring are fit for the new environment.
Over 90% of bird species regularly engage in social monogamy. A male and a female will pair off, sharing territory and engaging in social pair behavior for at least one breeding season, although many will remain monogamous for many years. However, researchers have found that some chicks are actually fathered by other birds than the ones who act like their fathers, taking care of the nest. Also, a pair of birds may act monogamous for a few years, and then ‘divorce’, finding other mates in subsequent years. Exposure to a variable climate drastically increases the chances that a bird will engage in extra-pair copulations or will find a new mate for the season.
For example, birds with large beaks are sexually selected for in dry climates, where they are better at eating large seeds; birds with small beaks are sexually selected for in rainy climates, where they are better at eating tiny seeds. It is easy for a female to select her mate in a stable wet or dry climate, but if the climate is variable, she will seek variability. This occurrence is becoming more and more prevalent with recent global warming.
Posted by Erica Fitzpatrick (1)