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Colorful birds make spring extra lively. But what gives them their hue

Vaseline

Birds have some of the most vibrant colors among land animals. The tropics are often known for the brightest birds, but American birds also display a wide range of striking hues.

But how colorful are our bird friends?

USA TODAY analyzed more than 500 photos of bird species from the Macaulay Library at the Cornell Lab of Ornithology, whose extensive media collection helps researchers identify and study color anomalies and rare bird colors. The species was chosen based on data from Project FeederWatch, a citizen science program at Cornell Lab that allows people to submit sightings of birds they have seen locally.

Using a machine learning algorithm, we determined the dominant color of each bird photo.

Let’s take a look at the American kestrel, one of the smallest and most colorful falcons in the US. It can be seen all over the country, hovering over open plains in search of insects to eat. Running the photo through a machine learning algorithm created this color palette for the bird.

The machine learning model determined that the dominant color for this bird is dark gray, meaning that this color group contained the most pixels. We performed the same analysis for all 559 bird species, resulting in a rainbow of colors representing American birds.

It is important to mention that the dominant color we get depends on the lighting of the photo, the time of year it was taken, the sex of the bird and its age.

Bird colors do more than just captivate human spectators. They also serve utilitarian purposes, indicating the overall quality of the environment and playing an important role in a bird’s survival and courtship behavior.

“Birds are sentinels of the environment,” says Allison Shultz, associate curator of ornithology at the Natural History Museums of Los Angeles County in California.

“It’s the artist in me that really fell in love with the colors of birds,” Shultz said, “but it was the biologist in me that discovered why they are so important and that they are actually worth studying.”

How do birds get their colors?

Understanding bird coloration combines biology and physics. There are two main ways birds get their color: pigmentation and the physical structure of the feather – sometimes a combination of the two.

Pigments are the chemicals in animal and plant cells that provide color and absorb and reflect certain wavelengths of light.

Birds acquire certain pigments, such as carotenoids, by eating fruits, seeds or insects. Carotenoids produce the bright red, yellow and orange hues you see in birds, and they are the same pigments that give carrots and pumpkins their distinctive color.

The other way birds achieve their appearance is through structural colors, which result from the interaction of light with the microscopic structures in feathers. Tiny air bubbles in the feather refract and scatter the light, creating vibrant colors that we can perceive.

Imagine the surface of a soap bubble or a rainbow-like oil slick. These phenomena, along with the brilliant blue wings of morpho butterflies, are examples of structural colors at play.

The northern cardinal, a classic red bird, has pigment in its feathers that absorbs all wavelengths except the red, which are then reflected back to us.

Carotenoid-based colors are often used as an indicator of a male bird’s quality, Shultz said. Brighter colors are often associated with superior genes, a stronger immune system and higher reproductive success.

This concept, known as “redder is better,” reflects the idea that brighter birds make better mates, says Richard Prum, an evolutionary ornithologist who teaches at Yale University. However, Prum disagrees, saying the concept is a problematic way of “bringing beauty into the world and turning it into usability.”

While several North American birds display apparently green plumage, turacos, native to sub-Saharan Africa, stand out as the only birds that are truly green. Unlike other species, turacos owe their color to a copper-based pigment called turacoverdin.

The common grackle and many glittering hummingbirds exhibit iridescence, like the way a prism splits light in a rainbow. Their iridescent feathers change color depending on the viewing angle, adding to the allure.

Colors of a bird

While bird species dazzle with countless colors, a single bird usually has multiple colors of its own, which our color palettes above do not represent.

The colors that birds have come down to evolutionary trade-offs and selective pressures, Prum said.

The strongest pressure is what drives a bird’s feathers in a certain way, Shultz said, whether it’s to impress a mate, blend in or stay cool in a warm place.

While bright colors can be great for social and sexual signals, they are not as useful for avoiding predators.

Bright pops of color often indicate colors used for social interactions. It can be a way of saying, ‘join my flock. We are members of the same herd,” Prum said.

For this reason, these vibrant spots often appear on a bird’s crown, throat or chest — areas that are opposite to other birds, Shultz said. A bird’s back is typically darker and more cryptic, which helps with camouflage. This adaptation, known as countershading, allows the bird to blend in with its surroundings and avoids drawing attention to itself.

For example, male ruby-crowned queens may display a scarlet crown when excited, or keep it hidden when necessary.

Feathers that contain melanin are stronger, Shultz said, which is why birds often have dark wing feathers to help them in flight.

Do colors change?

Even within the same species, color can vary depending on age, season and sex.

Birds undergo molting, the process of shedding old feathers and growing new ones, which can result in color transformations. Most birds experience an annual molt, usually after the breeding season, Shultz said, but species like American goldfinches replace their feathers twice a year.

“If you look at birds at certain times of the year, when they’re molting, they might look a little scrawny,” Shultz said. “That’s just because they’re growing new feathers.”

Moulting helps birds maintain optimal feather condition for flight and allows them to replace worn feathers and remove parasites, Prum said.

Young birds can also look different from their older counterparts. That’s because it takes time for birds to signal sexual maturity. Most songbirds reach this state after a year, but it can take up to five years for bald eagles to reach fully mature plumage.

Males and females can look different – ​​a phenomenon called sexual dimorphism. Females are often boring because they have different ecological and social behavioral needs, although the two sexes sometimes look identical, as seen in blue jays.

How do birds see colors?

As colorful as birds are to the human eye, we are actually “color blind when it comes to birds,” Prum said. That’s because birds see an even wider range of colors than humans.

“Birds live in a much more vibrant and colorful world than we do,” says Shultz.

Humans have three types of cones in our eyes for red, green and blue light. Birds have an extra type of cone that allows them to see ultraviolet light.

In addition to seeing a broader spectrum of colors, birds can also detect finer differences between colors. This means that birds can distinguish subtle nuances in shades of green that are imperceptible to us.

“Everyone always asks me, ‘Can you make bird-watching glasses?’” Shultz said. “And we can’t actually do that, because our brains are just not wired to neurologically process that kind of information.”

Curious about the birds you saw in this story? Click on a color to find out.

Contributing: Javier Zarracina

Sources: U.S. Fish and Wildlife Service National Digital Library, Getty Images.

Methodology: Photos were manually selected to find images of birds in a similar pose, with good lighting and for overall quality. The background was removed from all photos and each photo was put through the K-means algorithm to get the dominant color. K-means works by dividing a bird’s colors into different groups or ‘clusters’ to find the most representative colors. The color of each pixel is then assigned to the nearest cluster center. The cluster with the most pixels becomes the dominant color.

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