This Bird Lost Its Ability to Fly... Twice

Nature is filled with astonishing phenomena, and iterative evolution is a perfect example. This fascinating concept is dramatically exemplified in the Cuvier's rail, also known as the Aldabra rail (Dryolimnas cuvieri aldabranus), a bird that has lost its ability to fly not once, but twice in history. Located off the southeast coast of Africa, Aldabra Atoll provides a unique habitat for this remarkable species.


At first glance, the Aldabra rail might seem ordinary. With a size comparable to that of a chicken, its speckled gray back, a rust-colored head and torso, and a white throat, it stands out for one astonishing characteristic: it is the only bird currently unable to fly in the Indian Ocean, a survivor from a group that once included the dodo (Raphus cucullatus). This unique status is the result of a remarkable evolutionary process, illustrated by a 2019 study published in the Zoological Journal of the Linnean Society.

The story begins around 136,000 years ago when Aldabra Atoll was submerged, leading to the extinction of many species, including a subspecies of rail that was flightless. When the atoll resurfaced about 18,000 years later, the white-throated rail, capable of flight, recolonized it. Over time, these birds evolved again into a flightless form, a phenomenon supported by the discovery of fossils showing heavier and more robust legs dating to about 100,000 years ago, indicating a loss of flight ability.

This evolution towards flightlessness appears to have been advantageous in this isolated environment. Birds, laying their eggs on the ground, benefit from strong legs to swiftly move around right from hatching, a trait crucial for survival. The iterative evolution of the Aldabra rail highlights a fascinating aspect of evolution: nature's ability to follow similar paths under similar environmental pressures.

The case of the Aldabra rail is unique in the annals of biology, representing the only known instance of a bird becoming flightless twice through the same ancestor. This discovery illustrates not only the plasticity of evolution but also highlights the importance of Aldabra Atoll as a natural laboratory for studying evolutionary dynamics.