Darwin’s theory that tropical birds are more colorful proven by recent study


If you’ve ever visited a tropical location, you may have noticed that the feathers of birds appear shinier than those in other parts of the world. It turns out that the color of a bird’s plumage varies depending on the latitude.

During the 1800s, three European scientists who continued expeditions in the tropics – English naturalist Charles Darwin, British biologist Alfred Russel Wallace and German geographer Alexander von Humboldt – were amazed by the particularly vibrant colors of the flora and fauna they saw, and they issued the hypothesis that the animals became more colorful as one approached the equator, reported Phys.org.

From December 1831 to October 1836, Darwin and the captain and crew of HMS Beagle took part in a British government-sponsored expedition to survey the coast of South America, said the American Museum of Natural History. Darwin spent two-thirds of his time on land, much of it exploring and collecting specimens from the wilderness of Brazil, Chile, and Argentina, as well as the Galápagos Islands.

Wallace spent eight fascinating years in the Isles of Malay Archipelago, from 1854 to 1862, where he collected specimens, had an attack of malarial fever which led to his own theory of the survival of the fittest, and sent Darwin an essay. Titled “On the tendency of varieties to deviate indefinitely from the original type,” the article offered Wallace’s evolutionary theory of natural selection, which Darwin said had a “striking” similarity to his own, The New reported. Yorker.

From 1799 to 1804, von Humboldt set out on an expedition that took him through Venezuela, Cuba, Ecuador, Peru and Mexico, where he collected thousands of plant species and made sociological, socio-economic, geological and anthropological observations, according to a study published in the Annals of the Brazilian Academy of Sciences.

Recently, biologists from the University of Sheffield in England used artificial intelligence technology to confirm the theory of European naturalists that organic color vibrancy increased as one approached the tropics, Phys reported. .org. The results of their study“Latitudinal gradients in avian colourfulness”, were published in the journal Nature ecology and evolution.

“Darwin, Wallace, and von Humboldt all traveled to the tropics from their European places of origin and were clearly impressed by the variety of colors they encountered there, compare[d] to the species they [were] familiar in Europe. For example, von Humboldt in particular remarked frequently in his writings about the “mixtures of colors” he encountered, and you can sense his surprise when he writes about the “colors of birds, fish, even crayfish (sky blue and yellow) !” Dr. Christopher R. Cooney, an independent National Environment Research Council (NERC) researcher at the University of Sheffield and lead author of the study, told EcoWatch in an email.

Cooney and his colleagues examined more than 4,500 species of songbirds in the order Passeriformes, known as passerines, in their effort to prove the hypothesis. Passerines are distinguished by toes made for perching and comprise more than half of all birds.

Using an artificial intelligence technique called “deep learning”, the scientists obtained data from the pixels of three photographs of adult bird plumage obtained from Britain’s Tring Museum of Natural History.

According to MathWorks, deep learning is a subset of machine learninganother artificial intelligence technique that teaches computers to learn by example like humans.

“In deep learning, a computer model learns to perform classification tasks directly from images, text, or sound. Deep learning models can achieve state-of-the-art accuracy, sometimes exceeding human performance said MathWorks on its website.

The researchers used machine learning to help them identify the pixels that represented the birds’ plumage in the photographs.

“[I]In our case, we did not use machine learning to distinguish between different colors, but only to help us locate the position of the bird in our photographs of museum specimens. In other words, the machine learning helped us identify the right pixels in the image to analyze (i.e. those matching the bird’s plumage), while we measured the colority ( i.e. color diversity) using different techniques that take into account how the birds themselves perceive color,” Cooney told EcoWatch.

Birds are able to see ultraviolet lighta facet of color invisible to humans, explains the Natural History Museum in London.

“[T]To measure color in a way that represents color from a bird’s perspective, we need to measure colors that we can’t see,” Cooney said, as reported by the Natural History Museum in London.

Using the deep learning technique on photographs they had taken of the plumage of adult birds from the Tring Museum of Natural History collection, the scientists were able to identify 1,500 different color areas on the plumage of each bird, order the birds by color, and juxtapose the rankings with their places of origin, reported Phys.org.

The results confirmed the hypothesis of Darwin and his contemporaries that the color of bird feathers becomes more vibrant at latitudes closer to the equator. In fact, Cooney said birds closer to the equator tend to be 30% more colorful, the Natural History Museum in London said.

But why are birds more colorful in the tropics?

Wallace’s theory was that the “lush vegetation of the tropics” served as natural year-round camouflage, while the plumage of northern birds must have been adapted to leafless winter trees, Phys.org reported. Cooney noted that some of the predictions made by Wallace were supported by the study results.

“By examining large-scale patterns, we found that color was highest in birds in dense, closed forest habitats (such as rainforests) and in birds consuming fruit and floral nectar, all of which are two more prevalent at tropical latitudes,” Cooney told EcoWatch. . “This suggests the need for bright visual communication in dark tropical forests and the ability to acquire chromogenic compounds in the diet as two potential drivers of this pattern. We also found an association between color and tree diversity. bird communities, i.e. the average number of songbird species coexisting in the same location.This finding supports the idea that increased coloration can help equatorial species distinguish themselves from others in species-rich tropical communities.

“Structural” pigments and processes are used to achieve the spectacular colors of the birds.

“Birds can be colored in many different ways, but being colored often involves displaying colors produced by several different coloring mechanisms. For example, dark colors such as blacks and browns are produced by a pigment called melanin which is deposits in feathers. Similarly, brighter colors such as reds, oranges and yellows are produced by depositing a different set of pigments called carotenoids,” Cooney explained. “Unlike these ‘pigmentary’ color mechanisms, some birds can produce color using “structural” mechanisms, which involve small-scale structural changes to feathers to reflect certain wavelengths of light. In particular, many of the blues, purples, and ultraviolet colors of birds are produced by structural mechanisms… [B]birds with the most colorful plumage (such as the Paradise Tanager) will likely produce these colors using a variety of mechanisms.

It remains to be seen how the climate crisis will affect the coloring of animals around the world.

“[U]Fortunately, it is not yet clear how climate change (and other forms of environmental change) will affect animal color trends. However, this is an increasingly active area of ​​research and hopefully large animal coloration datasets like ours will allow us to further investigate the relationship between color and color. climate, and so shed light on the implications of climate change for global hair color trends,” Cooney said.


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