Climate Change Has Led to a Reversal of Sexually Selected Traits in Flycatcher Populations

A team of scientists has discovered that climate change is affecting the evolution of small passerine birds called collared flycatchers. After warm seasons, male forehead patches are selected against when they had previously been an indicator of reproductive success. Females are losing interest in the ornaments as average temperatures increase. The findings are in a paper that was just published in the journal Nature Ecology & Evolution.

Collared flycatchers (Ficedula albicollis) are small migratory birds that primarily eat flying insects, as the name suggests. Male collared flycatchers have large white patches on their foreheads, which contrast with the surrounding black feathers. The trait is purely ornamental and had been enhanced by sexual selection—female flycatchers preferred males with large patches. Larger patch sizes were previously linked to higher reproductive success.

Researchers from Uppsala University in Sweden analyzed data from a study of collared flycatchers that ran from 1980 to 2014. The study included a total of 10,842 individual flycatchers, representing 15 generations. The team found that larger patch sizes were no longer associated with higher reproductive success. In fact, large patches are now linked to decreased reproductive success and a lower chance of survival. After further data analysis, the team noticed a pattern. While females preferred large patches after cold breeding seasons, they reversed their preferences if the breeding season had been abnormally warm. Climate change has led to more warm breeding seasons, explaining the sudden negative selection against male ornaments.

The team’s findings show that a changing environment driven by climate change can lead to rapid evolutionary changes. A trait that used to be favorable in male flycatchers is now linked to decreased reproductive success, causing a reversal in sexual selection. The team isn’t sure why females changed their preferences as the breeding seasons became warmer. Although further research is necessary to fully understand this reversal, the authors emphasize the importance of considering the effects of climate change when studying evolutionary biology.


Evans et al. Climate change upends selection on ornamentation in a wild bird. Nature Ecology & Evolution (2017).

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