It's a biological mystery that has confounded scientists for over a century: How did the world's tiniest flightless bird find its way to one of the world's most remote islands?

The Inaccessible Island rail (Atlantisia rogersi), sometimes called the "bird from Atlantis," is only found in one place on Earth, the appropriately named Inaccessible Island in the South Atlantic Ocean, smack dab between Africa and South America. Because the bird is flightless, it's unclear how it could have found its way to such a far-flung place.

When the bird was first discovered, scientists guessed that perhaps its ancestors walked to the island at a time when sea levels were lower and a land bridge stretched out across the Atlantic. This theory also became the basis for assigning the bird its own genus, Atlantisia, an homage to the mythical lost city of Atlantis which, according to legend, had also been swallowed by the sea.

But it now appears that this theory was mistaken. A new genetic analysis of the bird has revealed what its closest living relatives are, which has, in turn, provided some telling clues about how its ancestors may have found themselves in such a distant locale, reports Science Daily.

It turns out, this itsy-bitsy flightless bird probably got to Inaccessible Island by flying there about 1.5 million years ago. Of course, at that time it was not flightless; the bird likely evolved to become flightless as an adaptation to its remote habitat.

Relatives around the globe

Although the Inaccessible Island rail is certainly an oddity, the study found that it has a distant relation to the dot-winged crake in South America and the black rail found in both South and North America. These birds are adept flyers, known to colonize habitats far and wide.

"It seems that rail birds are extremely good at colonizing new remote locations and adapting to different environments," explained evolutionary biologist Martin Stervander, who conducted the research.

It might seem unusual for a bird so adept on the wing to ever give up the ability to fly for a life confined to the ground on a small island, but it's a fairly smart adaptation. Flying takes a lot of energy and resources, and resources aren't plentiful on small islands in the middle of an ocean. Furthermore, there are no land predators on Inaccessible Island, so there's no need for wings to escape. Instead, the bird is able to fill the niche that tiny rodents might occupy elsewhere, scurrying around through the vegetation.

"The bird has not had any natural enemies on the island and has not needed to fly in order to escape predators," said Stervander. "Its ability to fly has therefore been reduced and ultimately lost through natural selection and evolution over thousands of years."

So, mystery solved. But this bird is truly one-of-a-kind, the last surviving member of a lost lineage that somehow found its way to a very unlikely habitat, and its rarity underscores the importance of making sure that it's protected. For now, Inaccessible Island is relatively pristine, with few introduced species that might compete with the bird. It will be important for conservationists to ensure that it stays this way.