Over the past 30 years, Swiss barn owls have become more reddish-brown and more heavily spotted. By analysing the genomes of more than 3,000 birds, scientists at the University of Lausanne identified the genetic variants linked to these changes in plumage and revealed natural selection at work. Their findings, published in Nature Communications , show that evolution can happen rapidly in the wild.
From pure white to deep reddish-brown through all variations of golden brown, barn owl plumage varies remarkably from one bird to another. Some owls have only a few faint dark spots on their chest, while others display many more, much bolder markings.
Research at the University of Lausanne (Unil) has shown that these features are more than cosmetic. Plumage colour is linked to fertility and hunting strategies, and therefore to diet. White barn owls, for example, use moonlight to their advantage when attacking prey (see this news , in French). Spotting, meanwhile, is associated with immunity and the ability to cope with stress. Birds with large black spots appear to withstand certain stressful conditions, such as food shortages or parasites, more successfully.
This diversity is not fixed. A study led by Tristan Cumer , a research fellow in the Department of Ecology and Evolution at Unil’s Faculty of Biology and Medicine, in the team of Professor Jérôme Goudet , shows that Swiss barn owls have gradually become more reddish-brown and more heavily spotted over the past 30 years. The findings were recently published in Nature Communications .
“Drawing on the exceptional volume of data collected by Alexandre Roulin and his group, who have monitored these birds of prey in the field for decades, we were able to sequence the complete genomes of more than 3,000 owls and identify the DNA variants associated with colour and spotting. This is one of the most in-depth genetic analyses ever conducted on a wild population,” says Jérôme Goudet, last author of the study, also affiliated with the SIB Swiss Institute of Bioinformatics .
The scientists pinpointed genetic regions that play a major role in the birds’ appearance. These include MC1R, a gene already known to affect pigmentation, and a region on a sex chromosome whose contribution to colour and spotting the researchers were able to clarify.
“This is one of the most in-depth genetic analyses ever conducted on a wild population.”
Prof. Jérôme Goudet, Department of Ecology and Evolution, Unil
The move towards redder, more heavily spotted plumage is not simply due to chance. By examining how genetic variants associated with colour and spotting became more or less common over time, the Unil biologists detected the effects of natural selection. “We compared the changes observed in the population with simulations in which evolution was entirely random. A genetic variant associated with reddish-brown plumage became far more common than chance alone could explain. Only simulations that included natural selection reproduced the changes we observed,” explains Tristan Cumer, first author of the paper. “Conducted in collaboration with the Swiss Ornithological Institute in Sempach , this study is one of the rare cases in which the genetic basis of recent evolution has been traced with such precision in the wild. This kind of demonstration is much harder in animals living in their natural environment than in a laboratory,” adds Jérôme Goudet.
“A genetic variant associated with reddish-brown plumage became far more common than chance alone could explain. Only simulations that included natural selection reproduced the changes we observed.”
Dr Tristan Cumer, Department of Ecology and Evolution, Unil
One essential question remains: why are barn owls becoming redder and more heavily spotted? Although the study clarifies the genetic basis of this evolution, the factors driving it have yet to be identified. Alexandre Roulin, professor in the Department of Ecology and Evolution and a co-author of the study, suggests several possibilities: “A change in prey availability may have favoured reddish-brown barn owls, which eat more voles, whereas white owls tend to feed more on wood mice. The increase in spotting could be linked to greater environmental stress. Despite the striking differences in colour between individuals, it remains extremely difficult to determine which ecological factors explain these variations.”
“We also do not know whether plumage colour is itself the trait directly favoured by natural selection,” says Jérôme Goudet. “MC1R plays a role in pigmentation, but it is part of the melanocortin system, which has also been linked to other traits, including stress responses and aggression. Selection may therefore be acting on one of these traits, with the change in the owls’ appearance simply arising as a consequence.”
The findings are part of a research programme led by Jérôme Goudet and his team for almost a decade. Their goal is to decode the barn owl genome and establish the species as a model for studying evolution in the wild. The researchers have sequenced and assembled the species’ reference genome , reconstructed its evolutionary history across Europe and the Mediterranea n, investigated genetic recombination , which reshuffles DNA from one generation to the next, and studied how mutations arise and are passed on within populations. “Research on this scale is possible because field teams, genomics specialists and members of the Faculty of Biology and Medicine’s core facilities work together,” says Professor Goudet.
The work is continuing. Computer analysis of photographs will allow the team to measure colour and spotting more precisely. The researchers also plan to use genetic data to reconstruct the plumage colour of birds that died very young and determine whether particular plumage features are associated with better chances of survival.
Beyond the case of barn owls, the Nature Communications study reminds us that evolution does not take place only over millions of years. Major genetic changes can also occur within a few decades. In this case, 30 years, around ten generations, were enough for the effects of natural selection to become detectable. “The study carries an encouraging message: it shows that species living in the wild can evolve over a short period. This capacity for rapid adaptation could help them cope with environmental change, including climate change,” concludes Tristan Cumer.
Nature Communications
Animals
Genomic bases of short-term evolution in wild barn owls revealed by long-term monitoring and population-scale sequencing
12-Oct-2026