Aldabra Rail: The Avian Resurrection – Evolving Twice from Extinction
Off the southeast coast of Africa lies the Aldabra atoll, a collection of coral limestone islands that once sank beneath the waves, causing the extinction of the flightless Aldabra rail 136,000 years ago. However, this unassuming bird has defied the odds by evolving to be flightless not once, but twice.
Resembling a chicken in size, the Aldabra rail boasts a flecked gray back, a rusty red head and chest, and a white throat. As a subspecies of the white-throated rail, it stands as the sole surviving flightless bird in the Indian Ocean, a testament to the impact of human-driven extinction, particularly that of the dodo.
In 2019, a study published in the Zoological Journal of the Linnean Society delved into the fossil record of Aldabra rails. The research uncovered evidence of a flightless rail population on the atoll prior to its submersion, signifying a significant shift in the fauna at the time.
The submersion, lasting until approximately 118,000 years ago, led to the extinction of the flightless rail subspecies. Yet, as the atoll resurfaced, the white-throated rail, capable of flight, recolonized the region and initiated a second evolution toward flightlessness. Leg fossils dating back around 100,000 years indicated a trend of increased weight and robustness, pointing to the loss of flight capabilities.
The environment played a crucial role in shaping this evolutionary path, as flightlessness proved advantageous for these birds. With the habit of laying eggs on the ground, the Aldabra rail’s strong legs facilitated immediate post-hatch survival. Julian Hume, lead author and paleontologist at the Natural History Museum, London, noted that pectoral and wing muscle development lags in rails, making flightless adaptation beneficial.
The Aldabra rail’s unique story involves what scientists term “iterative evolution,” a process where a species becomes extinct, only for another to evolve similar traits and essentially resurrect the original species. This extraordinary occurrence, according to Hume, is unparalleled, representing the same ancestral bird evolving into flightlessness twice.
In summary, the Aldabra rail stands as a remarkable example of avian resilience, overcoming extinction through iterative evolution and adapting to its environment by evolving flightlessness not once, but twice.