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.