Rare Three-Species Hybrid Warbler Discovered

Declining Population of One Species May Play a Role


It's exciting to see what the future may hold for this very rare bird. Photo: Lowell Burket

Birders have a new bird species to add to their birding wish list with the discovery of a rare three-species hybrid warbler.

Scientists have shown that a bird found in Pennsylvania is the offspring of a hybrid warbler mother and a warbler father from an entirely different genus.

Introducing the rare Three-Species Hybrid Warbler. Photo: Lowell Burket
Introducing the rare Three-Species Hybrid Warbler. Photo: Lowell Burket

This is combination never recorded before now, which resulted in a three-species hybrid bird.

The finding has just been published in the journal Biology Letters.

eBird Sighting Leads to Rare Find

“It’s extremely rare,” explains lead author and Cornell Lab of Ornithology postdoctoral associate David Toews.

“The female is a Golden-winged/Blue-winged Warbler hybridalso called a Brewster’s Warbler. She then mated with a Chestnut-sided Warbler and successfully reproduced.”

Graphic shows predicted family tree of warblers leading to the three-species hybrid. Blue-winged, Golden-winged, and Brewster's Warblers by Liz Clayton Fuller; Chestnut-sided Warbler from del Hoyo et al. (2018) Handbook of the Birds of the World Alive; new hybrid by Jillian Ditner. Graphic courtesy of the Cornell Lab of Ornithology
Graphic shows predicted family tree of warblers leading to the three-species hybrid. Blue-winged, Golden-winged, and Brewster’s Warblers by Liz Clayton Fuller; Chestnut-sided Warbler from del Hoyo et al. (2018) Handbook of the Birds of the World Alive; new hybrid by Jillian Ditner. Graphic courtesy of the Cornell Lab of Ornithology

A dedicated bird watcher and contributor to eBird.org in Roaring Spring, Pennsylvania, first noted the oddity in May 2018.

Lowell Burket says he spends time birding and relaxing in the woods on a family-owned property where he also likes to take photos and video of birds.

He noticed in a video a male bird that sang like a Chestnut-sided Warbler but had some of the physical characteristics of both Blue-winged and Golden-winged Warblers.

Male Chestnut-sided Warbler singing. Photo: Lowell Burket
Male Chestnut-sided Warbler singing. Photo: Lowell Burket

Burket saw the bird again many times, reported it to eBird, and got in touch with researchers in the Cornell Lab’s Fuller Evolutionary Biology Lab.

“I tried to make the email sound somewhat intellectual, so they wouldn’t think I was a crackpot,” says Burket.

He says having the photos and video helped.

Three-Species Hybrid Warbler Confirmed

Within a week researcher David Toews came down and they found the bird again and collected a blood sample and measurements.

“It was a very interesting and exciting morning for us. A few days later I got a text message from Dave saying, ‘You were right!!!’,” he says.

The key to identifying the triple-hybrid’s parents came from genetic analyses.

“We looked at the genes that code for different warbler colors,” Toews explains.

“This way we could recreate what the hybrid’s mother would have looked like—the avian equivalent of a detective’s facial composite, but generated from genes. We confirmed that the mother would have looked like a Brewster’s Warbler and the father was a Chestnut-sided Warbler,” adds Toews.

Three-Species Hybrid Warbler. Photo: Lowell Burket

Rare Hybridization

Hybridization is common among Golden-winged and Blue-winged Warblers, and this has been of particular concern for Golden-winged Warblers which have declined dramatically in some populations.

But hybridization has never been recorded between these species and Chestnut-sided Warblers. This kind of rare hybridization event may also occur more often in the declining warbler populations of Appalachia because there is a smaller pool of mates from which to choose.

“That this hybridization occurred within a population of Golden-winged Warblers in significant decline suggests that females may be making the best of a bad situation,” says Toews.

“It also tells us that wood-warblers, in general, have remained genetically compatible long after they evolved major differences in appearance.”

It's exciting to see what the future may hold for this very rare bird. Photo: Lowell Burket
It’s exciting to see what the future may hold for this very rare bird. Photo: Lowell Burket

Will the bird’s mixed ancestry confuse potential mates and make him a pariah or will he be able to find a mate and successfully produce offspring?

Scientists are going to keep an eye on this location to see what the future may hold for this very rare bird.

Next Rare Bird Discovery Can Happen to You

And Lowell Burket declares he’s a bird watcher for life.

“I had literally zero knowledge about birds until seven years ago,” he says.

“And now I end up discovering what appears to be a first-of-its-kind bird. It can happen to anybody!”

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