Some 1,36,000 years ago, the Aldabra rail went extinct from the atoll of Aldabra in the Indian Ocean. Originally from the Madagascar islands, the white-throated rail migrated to Aldabra. Over time, they lost their ability to fly as it was a vestigial(not needed anymore) act. They had no natural predators on this island and hence the ability to fly was unnecessary. But eventually, the tiny island sunk under water, wiping out the entire flora and fauna, including the rail. The inability to fly meant it had nowhere to go to, and ended up succumbing.
What happened later was truly incredible. The Aldabra rail found its way back to the island once the water had receded. And that too happened over and over. This unique phenomenon is called iterative evolution, where a species re-emerges over and over after going through extinction at different points in the past. It’s basically the repeated evolution of a species from the same ancestor at different times in history. In a few thousand years, when the sea levels receded, the birds re-colonized Aldabra.
In a study published in the Zoological Journal of the Linnean Society, the team studied the fossils of the bird’s wing bones from before and after the submersion of Aldabra. The bones showed an advanced state of flightlessness. Even the ankle bones highlighted a higher preference for walking.
“Conditions were such on Aldabra, the most important being the absence of terrestrial predators and competing mammals, that a rail was able to evolve flightlessness independently on each occasion,” explained David Martill, coauthor of the study.
Madagascar was also the home to the Dodo, another flightless bird that is now extinct. Due to occasional overpopulation of the rail on the Madagascar island, flocks would often fly out and places like Aldabra ended up being the more favourable option. This means that one species of birds from the Madagascar gave rise to two separate species of similar flightless rails in a gap of a few thousand years. The Aldabra rail can be found on that island even today.