Small flight­less bird mys­tery solved


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 2 500km 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 3 500km 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.


The In­ac­ces­si­ble Is­land rail bird was the sub­ject of re­search con­ducted by among oth­ers, UCT sci­en­tists, who in­ves­ti­gated how the world’s small­est flight­less bird alive to­day landed on an iso­lated is­land in the south­ern At­lantic Ocean. |

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