Few people have ever seen a Jerdon's courser (Rhinoptilus bitorquatus), a critically endangered nocturnal bird that lives in a tiny scrub forest in southeastern India. And until recently it was thought that no one had ever seen a Jerdon's courser nest or egg. But it turns out that a single egg from one of these rare birds has been gathering dust in a museum drawer in Scotland, of all places, for almost a century, just waiting to give up its secrets.

This tiny egg—smaller than three centimeters—had been hiding in the collections of the University of Aberdeen zoology museum for decades but had never been catalogued. It came to Scotland nearly 100 years ago as part of a group of Indian eggs that a veterinary surgeon named Ernest Meaton gathered around 1917. The collection, which was donated to an Aberdeen grammar school in 1919, made its way to the zoology museum in the 1970s. And there it sat, unexamined, for many more years.

Then, in 2008, Alan Knox, the university's emeritus head of museums, started going through the museum's drawers of uncatalogued eggs. He found the egg, which surprisingly was actually labeled as coming from a Jerdon's courser. "It was one of those eureka moments—finding something nobody else knows about, something so rare and exciting," Knox said in a press release. "I could hardly believe my eyes."

The 1917 date is particularly notable because at that time the Jerdon's courser was already thought to be extinct. The naturalist Thomas C. Jerdon first described the species scientifically in 1848, but after 1869 no one saw any of the small (27-centimeter), plover-like birds again for more than a century. In 1986 scientists rediscovered a population of the birds in Eastern Ghats, hundreds of kilometers from where Jerdon himself first found them. Today experts estimate there are fewer than 250 mature birds—possibly as few as 50—left.

Knox set out to confirm the egg's unlikely label. Comparison with eggs from other courser species showed that it was, in fact, unique. The next step was to carefully extract some DNA from the dried-up membranes inside the egg as well as from a Jerdon's courser toe that resided in the collection at the Natural History Museum in Tring, Hertfordshire. The DNA matched, and the egg's identity was confirmed.

Neither the egg itself nor the DNA gives us much new data about these little-studied, nocturnal birds. But Knox hopes that knowing what the eggs look like will give conservationists another tool to help in saving the species. Conservationists could use the help. Panchapakesan Jeganathan, a scientist with the Bombay Natural History Society, told Mongabay in 2010 that he saw the birds only three times during the eight years he studied them because the coursers are so fast, well-camouflaged and prone to hiding. But now, with at least this new egg description available, scientists and conservationists have at least one more thing to look for in preserving this critically endangered species.

Egg photo courtesy of the University of Aberdeen. Jerdon's courser llustration by Sarah Nicholls, used with permission. Visit her blog or Flickr page to see her great drawings of many other endangered birds