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By Chris Baraniuk,Features correspondent
Bachman’s warbler is one of 21 species declared extinct last year – but scientists are still discovering its secrets.
For more than 100 years, a tiny yellow and black bird has lain on its back: its eyes closed, its beak shut fast. “March 1890” reads the date on the paper tag tied around its foot – marking it out as one of seven Bachman’s warbler specimens in the ornithology collection at Cornell University, New York.
Last year, Bachman’s warbler was officially declared extinct by the United States Fish and Wildlife Service. It is the only songbird known to have gone extinct in North America in recent times. The four-inch-long (10cm) species was notable for its black throat patch and zezeze-like call, often finished with a brief flourish in the form of a sweeter-sounding note. It looks remarkably like two other warbler species from the US but, until very recently, no-one was quite sure how closely related they were.
More than a century after the individual now stored at Cornell last leapt into the sky, a team of scientists decided to study it and similar specimens. With today’s technology, they knew they could remove tissue from the birds’ feet and analyse the DNA contained within. This would help them better understand the genetic makeup of this enigmatic species, and pin down as best they could the origins of a songbird whose call we will never again hear in the wild.
Few people who ever caught a glimpse of a Bachman’s warbler alive would have been able to match what they were looking at to its official name. The first western record of the species dates to 1832, when it was first described by the Reverend John Bachman, a Lutheran minister. It took another 50 years after that for it to pop up again in natural history archives. Throughout the 20th Century, there are vanishingly few reliable sightings. There are several recordings of its call, and there’s one good colour photograph of a living individual from the 1950s.
In terms of evolutionary history, Bachman’s warbler was definitely one-of-a-kind
When David Toews looks at the only picture of a Bachman’s warbler, which shows it sitting proudly on a branch, he knows it is the closest he will get to witnessing a living specimen. “I don’t know of another more recent photograph,” says Toews, an assistant professor of Biology at Pennsylvania State University. “I usually like to get to know the species’ ecology and be in the wild [with it] – but obviously it’s just not possible.”
Bachman’s warblers were once found in the Gulf Coast region of the US. After it was first described, sightings become few and far between after the 1950s. There was one in 1988 – nearly 40 years ago. But reported sightings in 2001, which sparked extensive searches of Congaree National Park in South Carolina, ultimately yielded nothing.
For a long time, there was a question about the bird’s evolutionary origins. There are two other similar-looking warbler species – the Blue-winged and Golden-winged warblers. Because these birds are known to interbreed, some scientists have wondered whether Bachman’s warbler had some hybrid ancestry associated with them. Notably, the Golden-winged warbler has a dark throat patch just like Bachman’s warbler, as does one of the known hybrid forms of the two other warblers sometimes spotted in the wild today.
To try and find out what connection Bachman’s warbler might have to these visually similar, Toews and his colleagues turned to their DNA samples. In a paper published in June last year, they described their results. They found that there is no evidence for hybrid ancestry – and in fact, the extinct bird was “highly divergent” compared to its relatives.
The Bachman’s warbler’s genome is very clearly distinct from the Blue-winged and Golden-winged warbler genomes. There are hints that these birds might have had a common ancestor, also with yellow plumage or black throat markings. But in terms of evolutionary history, Bachman’s warbler was definitely one-of-a-kind.
“It was a sad finding,” says Toews. “This is something that was on its own evolutionary trajectory, probably for millions of years.”
Now Bachman’s warbler is gone. Scientists don’t even know exactly why it went extinct, though one theory is that the bird may have struggled with the loss of, or changes to, the swampy habitat that it preferred.
Only a handful of people alive today have witnessed a Bachman’s warbler in the wild. The species was never extensively studied – a ghost, as some have described it, that has passed from enigma to memory. Thanks only to genomics, we now know what a singular animal we have lost.
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