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For many of us, the tropics conjure up the idea of ​​lush vegetation teeming with vibrant and strikingly colorful birds, insects and other creatures. It has been a widespread belief that the world’s tropical regions are home to the most colorful species, an idea that probably dates back to the 19th century, when renowned naturalists, including Charles Darwin, commented on the rich diversity of colors found in the tropics. their high latitudinal homeland. And yet, until now, conclusive evidence for this geographic pattern in species coloration has been elusive.

An earlier study found that tropical birds from South America were more colorful than those from North America, with European birds being the least colourful. But other studies, such as those looking at birds off the east coast of Australia, found that it was the species living in arid regions and not near the equator that had the most intense plumage colour. Therefore, the issue remains unresolved.

In our new research, published in the journal Nature Ecology and Evolution, we have finally found that the trend appears to be true because tropical species of songbirds are actually more colorful than their non-tropical counterparts, as suggested by Darwin. . And we think that this may be partly due to the need to stand out in the crowd, due to the high concentration of different species living together in tropical communities.

Study of 4,500 songbird species

Using the global bird specimen collection at the UK’s Natural History Museum, we collected adult male and female specimens from more than 4,500 species of songbirds from around the world, from the tropical paradise tanager (Tangara chilensis) to the high latitude brown dipper (Synclus). Photographed digitally. Pallasi).

We chose songbirds (also known as passerines) because they represent about 60 percent of all bird species and are therefore well represented in museum collections. A state-of-the-art computer technology called deep learning that is capable of learning to process and classify large amounts of complex data from images helped us extract information from the thousands of pixels in each picture.

We were then able to measure the shade and intensity of the feather colors in each photo in terms of red, green, and blue light as well as ultraviolet, this was important because birds have wider vision than humans and they can’t see the ultraviolet. You can see the colours. light spectrum. Using this information, we generated accurate estimates of the chromaticity of each species, based on the number of distinct colors (or color loci) in each bird’s plumage.

When we mapped variation in species’ color scores across the globe, we found strong evidence that bird coloration is generally highest at the equator and decreases with increasing latitude, particularly toward the poles, Their plumage displays about 20%-30% more color than birds. At higher latitudes outside the tropics, whether north or south. Interestingly, this was true for both male and female birds, even though they can sometimes look very different from each other. So, we have proved Darwin’s observations to be correct, the next step was to investigate what factors could cause this color gradient.

advantage of color

There were several possible theories. Perhaps a more favorable climate near the equator in terms of temperature and precipitation, for example, allows tropical species to invest more energy in developing elaborate plumage colouration. Or perhaps the influence of ecological factors, such as the amount of light in their habitat, may have influenced the birds’ presence.

To test these hypotheses, we collected information about the environmental and ecological characteristics of the species in our study, and using data analysis to ascertain whether variables may help explain variation in coloration across species. . We found that birds of dense, closed forest habitats such as rainforests and those who eat fruit and flower nectar also had the highest color diversity.

Both of those traits are more common in tropical latitudes, so this suggests that two possible reasons for the evolution of color diversity may be the need for brightly colored visual communication (such as gestures and body posture) in deep tropical forests, and the ability to acquire. The ability to add color-forming compounds (such as carotenoids) from fruits in your diet. And there was also a positive association between colorism and diversity of bird communities.

The average number of songbird species living together in the same location increases dramatically toward the equator, so this increased coloration may help them differentiate themselves from all other birds in their rich tropical communities, which Avoiding potentially costly interactions with other species is an essential skill. Which may also include sexual intercourse. Going forward, pinpointing the location of global coloration hotspots in different regions and among different species will help us plan effective species and habitat conservation strategies that preserve color diversity.

As the 19th-century British naturalist Alfred Russell Wallace once said: There is perhaps no single quality of natural objects that makes us so pure and intellectually happy with their colours. We are indebted to generations to come for ensuring that the wonderful colorfulness of the natural world is not diminished.

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