Climate change is robbing birds of color

On April 3, 1860, in a letter to the American botanist Asa Gray, Charles Darwin expressed his frustration at the presence of peacocks’ conspicuous tails: “The sight of a feather on a peacock’s tail, every time you I look at it, it makes me sick!” Darwin confessed.

His discontent was that the peacocks’ tails contradicted his theory of evolution by natural selection, since rather than increasing the survival of peacocks, they seem to do the opposite.

Eleven years later, in 1871, Darwin proposed the solution to this (apparent) contradiction in his book The origin of man and selection in relation to sex. According to the British scientist, the function of showy features (ornaments) is not to increase the survival of their owners but rather their reproductive success. That is, the presence of conspicuous features, such as the tails of peacocks, is explained by sexual selection rather than natural selection.

A sign of health and quality

Currently, we know that ornaments function as signs of quality: they inform about the physical condition, health, or personality of the possessors.

Furthermore, we also know that ornaments convey honest information because they are expensive to produce. This means that only the highest quality individuals are capable of producing the most striking ornaments.

However, despite the fact that our knowledge of ornaments has come a long way since Darwin’s time, there are still many open questions about its evolution.

Effects of climate change

Climate change and its effects on fauna and flora have received much attention from the scientific community. Most of the studies have focused on exploring the effects of climate change on the beginning of flowering in plants or the date of laying in birds.

In contrast, the effects of climate change on other features, such as ornaments displayed by many species of animals and even plants, are virtually unknown.

The importance of studying the effects of climate change on ornaments lies in the fact that their production costs vary depending on environmental conditions. When environmental conditions are good (for example, when there is a lot of food), ornaments are relatively cheaper to produce than when environmental conditions are bad (for example, when there is little food).

If climate change continues to worsen environmental conditions, the relative costs of signal production could increase. As the energy available to an individual is limited, this increase in signal costs could limit the energy investment in other vital functions such as survival, which could have negative consequences for the maintenance of the populations of a species.

Therefore, to understand and predict the responses of populations to climate change, it is important to study how it affects the expression of ornaments.

The case of the blue tit in the south of France

In a recent study, scientists from the Center for Functional and Evolutionary Ecology in Montpellier and the University of the Basque Country have studied the effects of climate change on the ornamental colorations of the blue tit (Cyanistes caeruleus).

The blue tit is a small bird that is very common in European forests. It is characterized by having a very showy coloration. Its blue crown and yellow chest are especially striking.

Blue tits have received a lot of attention from the scientific community. Thanks to that we know that both their blue crowns and their yellow breasts work as signals informing about the quality of their owners.

Our study focused on two populations of blue tits from the south of France. One located in the vicinity of Montpellier and the other in the northwest of the island of Corsica, which have been studied for more than 15 years.

Every year between 2005 and 2019, we captured all the breeding blue tits in each population. Thanks to that we were able to obtain more than 5,800 measurements on the coloration and other characteristics of the blue tits.

less colorful plumage

The results of our study show that in both populations the blue and yellow coloration of blue tits has decreased between 2005 and 2019. In other words, currently in these two populations, the blue crowns and yellow breasts of blue tits are less conspicuous than when the study began.

Furthermore, in Corsica we found that in hotter and drier summers blue tits had less conspicuous colorations, both blue and yellow. This, together with the rise in temperature and reduction in rainfall in our study area, suggests that the reduction in coloration in this population is a consequence of climate change.

The blue tit is characterized by its blue, green, yellow, and black-and-white color patterns. David Lopez Idiaquez, Author provided

Interestingly, no significant changes in temperature or associations between temperature and blue tit coloration were detected in the population in the vicinity of Montpellier.

On the one hand, this tells us that the effects of climate change are not the same everywhere. On the other hand, the absence of association between color and climate suggests that ornamental colorations are sensitive to other environmental factors that should be explored in the future.

In summary, our study and others carried out on other species such as the collared flycatcher and dragonflies show that climate change is having a negative impact on the animals’ ornaments.

In future studies, we will need to explore the consequences of this impact on the ability of populations to adapt to climate change. In this way we will be able to understand its consequences not only for birds but also for ecosystems in general.The Conversation