The Aldabra rail, a unique and remarkable bird, inhabits the coral limestone islands of the Aldabra atoll, situated off the southeast coast of Africa, north of Madagascar. This flightless bird, a subspecies of the white-throated rail, holds a fascinating evolutionary history.
The Aldabra rail is the sole living flightless bird in the Indian Ocean, with its evolutionary journey closely tied to human-driven extinctions, such as that of the dodo. A 2019 study explored the fossil record of rails on Aldabra, revealing evidence of a flightless rail that existed before the atoll submerged beneath the waves approximately 136,000 years ago.
Extinction and Recolonization
The submersion event, lasting until around 118,000 years ago, led to the extinction of the flightless rail subspecies. However, after the atoll resurfaced, the white-throated rail, capable of flight, recolonized Aldabra. This marked the beginning of the rail’s second evolution towards flightlessness.
Analysis of leg fossils dating back to around 100,000 years ago indicated a shift towards heavier and more robust legs in the rails, suggesting the loss of flight capability. Flightlessness appears to be a beneficial trait in their environment, where the birds lay eggs on the ground. The development of strong legs assists newly hatched birds in survival.
The Aldabra rail’s remarkable journey involves evolving to flightlessness twice, a process known as “iterative evolution.” This phenomenon, where a species becomes extinct and is later replaced by another evolving identical traits, is a rare occurrence. In this case, the same ancestral bird lost and regained its ability to fly.
Multiple Choice Questions (MCQs) with Answers:
- Where are the Aldabra atoll and the Aldabra rail located?
- a) North of Europe
- b) Southeast coast of Africa, north of Madagascar
- c) South America
- d) East Asia
- What is the Aldabra rail’s connection to the dodo?
- a) They are distant relatives
- b) They share the same habitat
- c) Both are flightless birds affected by human-driven extinctions
- d) The dodo is a predator of the Aldabra rail
- What caused the extinction of the flightless rail subspecies on Aldabra approximately 118,000 years ago?
- a) Human activities
- b) Climate change
- c) Submersion of the atoll
- d) Introduction of new predators
- What evolutionary trait in the Aldabra rail indicates its adaptation to a flightless lifestyle?
- a) Longer beak
- b) Lighter and more delicate legs
- c) Heavier and more robust legs
- d) Larger wingspan
- What process describes the Aldabra rail’s evolution of flightlessness twice?
- a) Parallel evolution
- b) Convergent evolution
- c) Iterative evolution
- d) Adaptive radiation