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This White Red-tailed Hawk Isn’t Just Gorgeous—It’s Also a Rare Scientific Opportunity

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On a sunny February afternoon, Bryce Robinson, a PhD candidate at the Cornell Lab of Ornithology, was on the search for Red-tailed Hawks in the Oklahoma countryside. He was walking with his advisor and other researchers when suddenly they saw it: an all-white Red-tailed Hawk. “Everyone was in shock and awe at first,” Robinson recalls. “It looked like it was glowing.”

Robinson studies the Red-tailed Hawk subspecies harlani, a variant that has a distinct dark plumage. He catches the birds to gather genetic data, take photographs of their feathers, and put GPS transmitters on them. The hawk’s lack of coloration made it hard to tell whether it was the subspecies Robinson was interested in, but the opportunity to research such a bird was too exciting to pass up. While white Red-tailed Hawks aren’t unheard of, seeing one is like finding “a rare unicorn,” Robinson says. So the team set out their trap and caught the raptor, taking  measurement and samples and affixing it with a transmitter before letting it go. They hope the data the bird provides will help propel our scientific understanding of how individuals like this hawk get such striking plumage.

All-white birds have long been a source of fascination in the scientific community. At first, scientists only understood albinism, a genetic mutation that prevents an animal from producing pigment due to the absence of a specific enzyme. But “our sophistication in how we talk about birds that are white … has grown a lot in the past 30 years,” Robinson says. Scientists now have a variety of terms to capture plumage patterns outside of albinism, and attempt to discern if colorations are genetic, environmentally driven, or both.

Looking at this Red-tailed Hawk, experts agree that it is not an albino. Albinism would mean that the bird would have no color, period. The eyes would be red, says Robinson. But the captured bird had pigment in the beak and eyes, as well as a few brown feathers scattered on the back of its head.

This hawk is more likely leucistic, an umbrella term indicating that the bird’s “melanin pathways are broken,” says Allison Shultz, an ornithologist at the Natural History Museums of Los Angeles County. This means that certain cells in its body are unable to deposit melanin, turning feathers white instead of black and brown. A variety of abnormal plumages are often grouped under leucism, from birds with white spots to all-white birds. Under formal definitions, these white patches from leucism stay consistent throughout life and are caused by genetic mutations. However, without molecular testing, it’s hard to determine if this hawk has these mutations, says Robinson.

This hawk is more likely leucistic.

It’s also possible that the hawk is undergoing progressive graying, which Robinson proposed in a blog post about the striking raptor. With progressive graying, melanin production is deteriorating, causing feathers to get whiter as a bird ages. By examining the hawk’s molt patterns, Robinson and his colleagues determined that it is at least three years old. He says he’s heard of birders talking about hawks that get slightly whiter every year, so maybe this one’s plumage has slowly lost pigmentation. But pure white plumage from progressive graying is rare, says Hein Van Grouw, the senior curator at the Natural History Museum in the U.K. who wrote a 2021 paper about color terminology. It would be very difficult for a hawk to reach this level of white through progressive graying, even if the bird is well into adulthood, he says.

Van Grouw instead brings up another explanation: The bird was born unable to produce pigment but is slowly gaining the ability with age. He’s currently working on a paper explaining this developmental pattern that he has observed, where white birds slowly grow small patches of black as they get older. That could explain why the hawk has some plumage pigmentation, as well as dark eyes, feet, and a beak, he explains, since all-white leucistic birds tend to have paler beaks and feet. But whether this is the case can only be shown with time.

Thanks to the transmitter Robinson and his team put on the bird, we can now observe how the bird—and its plumage—ages over the coming years. Tracking it could not only perhaps provide some clarity on how the hawk got its colors, but also its life, he says. We know that melanin can help feathers become stronger, adds Shultz, but how a lack of melanin affects how a bird finds its mate, whether it can live as long, as well as other aspects of its life, remains a mystery. 

The birding community can also help augment our understanding of birds with irregular plumages. Birders and photographers see way more unusually colored birds than scientists, including many white Red-tailed Hawks throughout the continent. Adding these atypical sightings to platforms like eBird and iNaturalist can help researchers learn more about these plumage variations, says Shultz.

A part of that information gathering has already begun for this Red-tailed Hawk. A local birder has recently reached out to Robinson, informing him that they’ve seen this raptor in the Oklahoma City area for the past eight years. When it comes to his own data, Robinson probably won’t get a clearer picture of this hawk’s movements until October. He plans to post updates on his blog as the transmitter gathers more data. Until then, we can only admire the all-white plumage of this hawk, and the secrets it has yet to share.

 

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