Zebras, a children’s story says, became striped after being “half in the shade and half out”. Although the author, Rudyard Kipling, was not a biologist, there may be some truth to his story: research shows that when temperatures rise, animals become lighter in color, resembling the sun-exposed parts of the zebra in the storybook. In wet shadows, on the other hand, darker tones predominate.
As our planet warms and rain patterns change, the feathers and skin of many species are changing, often lighter. Snails In the Netherlands they are going from brown to yellow. In a species tropical bee In Costa Rica, the proportion of orange and blue individuals is increasing. lizards They are easing up in France, and a lot of them too insects and the birds all over the world “Due to global warming, one would expect the darkest species and the darkest individuals to decline,” he says. Stefan Pinkertecologist and evolutionary biologist at Yale University.
There are two main ways to color the skin, hair and feathers of animals. Some of the hues we perceive are due to the interaction of light with the microstructure of a feather or scale, think of a hummingbird changing color depending on the angle from which you view it. Others include pigments, light-absorbing molecules, carotenoids, which produce yellow, red, and orange colors, and melanins, which cause black, gray, brown, and rust-like colors.
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Melanin, the most common pigment in birds and mammals, can be affected by rising temperatures and changing rain patterns. “If you have more melanin in your skin or in your fur or feathers, then it tends to absorb more heat,” he says. Matthew ShawkeyAn evolutionary biologist at the University of Ghent in Belgium. This can be a disadvantage as the temperature rises, as it can cause the animal to overheat. On the other hand, if it rains more, pathogens tend to grow. Under these conditions, dark melanins can be protective because they “harden the tissues,” says Shawkey.
A A rule proposed by Charles Bogertan American herpetologist, in a 1949 paper, predicted that warmer climates should have a greater presence of ectotherms, or so-called cold-blooded animals, lighter in color and therefore less likely to overheat. (These animals, such as reptiles and insects, cannot regulate their own body temperature, and rely on external heat sources).
In recent years, science has not only confirmed Bogert’s rule, but has also extended it to endothermic or warm-blooded species. It’s just not frogs, toads, snakes and the radii which are lighter in warmer regions; birds are also lighter. A 2024 study of more than 10,000 bird species showed that in hot places, white and yellow win against the blue and black feathers.
With global warming, some animal populations are becoming even more vulnerable. Between 1967 and 2010, when temperatures in the Netherlands rose between 1.5 and 2 degrees Celsius, brown land snails he gave them a place. Dragonflies and damselflies in the UK between 1990 and 2020 it gradually got lightermoreover, as Pinkert and his colleagues found in a 2023 paper. And if you look closely at some dragonflies, you might notice that they now have less dark ornamentation on their wings.
in one final exam Conducted in North America, male dragonflies from 10 different species had the least melanin-based color spots on their wings during the warmest years between 2005 and 2019. Over the same period of time, even the pretty spots seemed to fade. Mediterranean blue tits—small birds, yellow-breasted and blue-colored, with a hat-like mark on the head. Between 2015 and 2019, blue tit populations around Montpellier, France, declined by approximately 23 percent, a change linked to local temperature increases.
Experiments confirm observational data: hot temperatures make animals lighter. In some cases, an individual may produce more or less pigment depending on the temperature. Live dancers damselfliesfor example, colors can change from dark to light to dark as the mercury changes throughout the day. male chameleon grasshoppers change from black at 50 degrees Fahrenheit (10 degrees C) to turquoise at more than 77 degrees F (25 degrees C). “If you grow many species of insects in cold temperatures, they develop darker, and if you grow them in warmer temperatures, they develop lighter,” he says. Kaspar DelheyEvolutionary biologist at the Max Planck Institute for Biological Intelligence in Seewiesen, Germany.
Such effects are not limited to insects. Field experiments in Spain showed this growing vultures nests exposed to more sunlight have paler feathers than those raised in more sheltered places. It wasn’t just that the birds were bleached by the sun; the melanin in their plumage did not deteriorate, as if destroyed by the sun. To begin with, there was simply less.
In addition to the individual ability to adjust color to temperature, populations of animals living in warming regions may become lighter as paler animals move into new areas. Genetic changes may also be at play, Pinkert says, but we still have a “critical knowledge gap” about how that evolution might play out.
Although Bogert’s rule is correct, in regions that remain hot and dry, such as the Mediterranean, if precipitation increases with temperature, species it can become dark instead of light In 1833 Constantin Glogerthe German ornithologist suggested that in wet places the feathers are black rather than white. One reason may be camouflage. In humid habitats, “there is more vegetation; backgrounds are darker, so a darker animal might be more camouflaged,” says Delhey. Another explanation for Gloger’s rule may be protection against pathogens, often they flourish in humid climates. 2020 exam 16 species of birds Feathers with more melanin are more resistant to damage from nesting bacteria. “The purpose of this molecule is to protect the organism from different sources of stress. For example, feathers that are black are stronger,” he says Alexandre RoulinAn evolutionary biologist at the University of Lausanne in Switzerland, who was not involved in the research. Research suggests that melanin molecules are not alone inhibit parasites but also strengthen cellscreating a barrier against pathogens.
When Delhey tested what happens when temperatures and precipitation increase with climate change, he found that, at least in birds, “the effects of humidity are generally much stronger.” Delhey and colleagues he mapped the colors of the plumage among all species of passerine birds, of which more than 5,000, to the climates where they live. Animals were lighter in warm and dry conditions, but darker in warm and humid conditions. Roulin and his colleagues found something similar in one 2024 exam Among the thousands of owl museum specimens collected worldwide between 1901 and 2018. The researchers showed that over time, plumage colors became lighter where the climate was warmer and drier, but darker where temperature and precipitation increased. “Where the climate change was stronger, the color change was stronger,” Roulin says.
However, they are changes in precipitation patterns caused by global warming so right rather than future temperature rises. Therefore, Delhey says, if he were to predict a general trend among animals, “based on the effects of temperature, they should be lighter.” Although cold-blooded animals, such as insects, may respond more to heat than humidity, he says, there is still no research on this.
In general, changes in animal coloration are expected to be subtle. “We’re not going to see such drastic changes, we’re not going to know the species,” says Delhey. From a biological point of view, however, “that small difference can tell whether a species can survive,” he says. Meanwhile, animals that adapt by changing colors can serve as a visual reminder of humanity’s enormous environmental footprint that has disrupted the entire planet. “You can track the impact of climate change with your eyes,” Roulin says.
