By Victoria Gill
Science reporter, BBC News
Sub-populations of the mockingbirds remain on two small islands
A rare mockingbird could be reintroduced to the Galapagos Islands - with the help of some specimens collected by Charles Darwin.
A team of geneticists extracted DNA from two birds that the famous naturalist collected in 1835.
By comparing this to DNA from living sub-populations on two other islands, the scientists revealed genetic clues about how best to conserve the birds.
They report their findings in the Royal Society journal Biology Letters.
The researchers used two specimens that Darwin and Robert Fitzroy - the captain of HMS Beagle - collected from Floreana Island during their trip to the Galapagos more than 170 years ago.
The Floreana mockingbird (Mimus trifasciatus) became extinct on the island soon after this famous expedition, mainly because of the human impact on its delicate habitat.
Today only two small sub-populations survive on two tiny satellite islets - Champion and Gardner-by-Floreana.
Survival of species
The study was led by biologist Paquita Hoeck from the University of Zurich in Switzerland.
Karen James, a Natural History Museum of London researcher who was also involved in the work, said the Floreana mockingbird was one of the rarest birds in the world.
"It was also important for Darwin's realisation that organisms might evolve independently on islands," she told BBC News.
Darwin knew about evolution, but nothing about DNA
The Charles Darwin Foundation, which carries out conservation research in the Galapagos, is collaborating with Durrell Wildlife Conservation Trust, to reintroduce the birds to Floreana.
But for this reintroduction to be effective, Dr James said, a population would have to be restored that was "as close as possible to what existed before".
To find out what this population would look like, the scientists needed to study the Floreana birds.
"There are very few of these specimens," Dr James explained. "But the Natural History Museum has two of them and they just so happened to have been collected by Darwin and Fitzroy."
Dr James and her colleagues were given the opportunity to take tiny samples from the toe pads of each historic specimen, from which to extract DNA.
The team found "genetic signals" in each of the two surviving species that were also present in Darwin's samples.
This revealed that the two sub-populations split from each other very recently. This split, the researchers said, was likely caused by the Floreana mockingbird becoming extinct.
Its extinction would have severed a "bridge" between the two populations - meaning that it was no longer possible for them to interbreed.
Even though they have evolved independently and become inbred, this study showed that the tiny sub-populations have retained much of the important "genetic variation" once found in the mockingbirds on Floreana.
This is good news for the survival of the species.
It has led the researchers to conclude that future conservation plans should focus on protecting "the two satellite populations in situ and establishing a single third population on Floreana".
This reintroduction could use birds from both islands, the researchers said, "to maximize genetic diversity".
Dr James said the project highlighted the importance of historic specimens.
"Though Darwin knew nothing of DNA, the specimens he and Fitzroy collected have, after 170 years of safe-keeping in collections, yielded genetic clues to suggest a path for conservation of this critically endangered and historically important species," she said.