Is global climate change altering the coloration of birds?

An investigation has explored the possible causes of an alteration in the coloration of the plumage of the blue tit (Cyanistes caeruleus).

The study has been carried out for 15 years in the south of France through a collaboration between scientists from the University of the Basque Country (UPV/EHU) in Spain and the Montpellier Center for Functional and Evolutionary Ecology (CEFE) in France.

The study, in which David López-Idiáquez, from the UPV/EHU, took part, focused on two populations of blue tits in the south of France, one located near Montpellier and the other in the northwest of the island of Corsica.

Every year between 2005 and 2019, all breeding blue tits from each population were captured. Thanks to this, the researchers from the two institutions were able to obtain more than 5,800 observations on the coloration and other characteristics of the blue tits.

The blue tit is characterized by its striking coloration: they have a blue crown and a yellow chest. The results obtained in the study show a decrease in both populations of blue and yellow coloration between 2005 and 2019. In other words, today, in these two populations the blue crowns and yellow breasts of blue tits are of average less colorful than at the time the investigation began.

“Our work suggests that environmental changes, and specifically climate change, could be the main reason why birds such as the blue tit are undergoing a change in their physical features, more specifically in the brightness and intensity of their coloration,” he says. David López-Idiáquez, researcher at the Department of Plant Biology and Ecology at the UPV/EHU.

“It has been observed how the trend in both sexes and populations is negative in terms of brightness and intensity of the coloration of the feathers, although in Corsica this change is more associated with the climate,” explains López. “The change in the color of the plumage seems to be the result of the combination between the rise in temperature (1.23 degrees Celsius) and the drop in rainfall (0.64 mm)”, she explains.

The blue tit is characterized by its striking coloration: they have a blue crown and a yellow chest. (Photo: UPV/EHU)

It may seem like it’s just a purely aesthetic change, but it’s just the opposite, as this change in plumage can have effects on the mating patterns of the species. “In these birds, traits such as color function as signals to indicate the quality of the specimen to other individuals, which are decisive, for example, when it comes to reproducing,” says David López.

“This study was possible thanks to the continuous monitoring of the two populations of blue tits for more than 15 years, which highlights the importance of having long-term studies to understand the effects of climate change on the ecosystems that surround us” , highlights.

When there is a variation in the territory, animal populations have 4 options: The first, to undergo a genetic change; the second, to undergo a plastic change (modification in physical characteristics without genetic changes); the third, emigrate; and finally disappear. “It is important to note that this change is not genetic but plastic, one of the ways to adapt to new environmental conditions,” he reveals.

Taking into account that the natural environment in the Basque Country is quite similar, although less hot, it is possible that the birds of the Basque Country are undergoing the same change, as David theorizes. In any case, there are only 4 studies of this type in the world, and none of them have been carried out in the Basque Country. Therefore, as David thinks, it would be very interesting to carry out more research like this not only at the Basque level, but at the state level as well”, he adds.

The study is titled “Long-Term Decrease in Coloration: A Consequence of Climate Change?”. And it has been published in the academic journal The American Naturalist. (Source: UPV/EHU)