Cape Town – Scientists from UCT are part of a global team that has solved the mystery of how the world’s smallest flightless bird alive today landed on an isolated island in the middle of the southern Atlantic Ocean, aptly named Inaccessible Island.
More than 2500km from any mainland, the tiny Inaccessible Island is uninhabited by people and mostly uninhabited by animals: no land mammals, reptiles, amphibians, butterflies or snails have been found there.
But it is the only place where the Inaccessible Island rail (Atlantisia rogersi), lives; a small bird with brown plumage, black beak and feet, and red eyes. It is flightless and weighs only 34g to 49g - less than a chicken’s egg.
UCT Percy FitzPatrick Institute of African Ornithology (PFIAO) director and study co-author Professor Peter Ryan said: “Birds of the rail family are extraordinarily good at colonising remote islands.”
Ryan has spent the most time on the otherwise uninhabited Inaccessible Island, where he is on a three-month expedition.
The study found that the birds either flew or were assisted by floating debris.
When the birds arrived on the island, they found a place free of predators and abundant food. Because they no longer needed strong wings to survive, over time, they evolved into a flightless species - something not uncommon among rails.
At least 32 isolated, living rail species have either lost their ability to fly or are much less capable of flying.
While visiting Inaccessible Island seven years ago, the researchers collected DNA from one male rail.
They sequenced this using next-generation sequencing techniques and compared with DNA sequences from other species of rail, including from South America and Africa which allowed them to establish which species the Inaccessible Island rail was most closely related to.
Their results show that the Inaccessible Island rail very likely originated from South America, where its closest living relative - the dot-winged crake - resides, more than 3500km away.
By looking at the extent of the differences between the two sister birds’ DNA and considering the amount of time it would take to accumulate these genetic changes, the researchers can tell that the Inaccessible Island rail probably immigrated around 1.5 million years ago.
The rails that live on the island have subsequently thrived and should continue to do so as long as no predators are introduced to the island. Having no introduced predators is extremely rare among the world’s islands.
Dr Martim Melo, research associate at the UCT PFIAO based at the Research Centre in Biodiversity and Genetic Resources at the University of Porto, Portugal, said many flightless rails lived on oceanic islands all over the world before the arrival of humans.
“Up to 1 600 species are thought to have lived on the Pacific islands alone, but people brought with them a variety of predators,” Melo said.