Saving Darwin's mockingbird

18 November 2009

A very rare mockingbird could be reintroduced to the Galapagos Islands thanks to specimens collected by Charles Darwin, it is reported in the Royal Society journal Biology Letters today.

A team of geneticists  have extracted DNA from birds that Darwin collected while visiting the islands in 1835. Darwin noticed the Floreana mockingbird’s evident difference from the specimens he collected on other islands. Thus, the former holds a special claim on being a first vital clue for Darwin’s theory of speication under natural selection.

By comparing the DNA extracted from the birds to that of living sub-populations on two other islands, the scientists have revealed genetic clues about how best to conserve the birds.

The Floreana mockingbird (Mimus trifasciatus) became extinct on the island soon after Darwin’s famous visit due in most part to human impact on its delicate habitat. Today only two small sub-populations survive on two tiny satellite islets - Champion and Gardner-by-Floreana.

The Charles Darwin Foundation, which carries out conservation research in the Galapagos, plans eventually to reintroduce the birds to Floreana.

The scientists obtained blood samples from the Champion and Gardner populations in 2006-2008 and small toe-pad samples from specimens collected on both satellite islets in 1905-1906 by a California Academy of Science expedition. They also analysed two specimens from Floreana itself collected in 1835 and held at the Natural History Museum in London.

The team found "genetic signals" in each of the two surviving species that were also present in Darwin's samples revealing that the two sub-populations split from each other very recently.  The study shows that these sub-populations have retained much of the important genetic variation once found in the Floreana mockingbirds.

The researchers have concluded that current and future management actions should focus on conserving the two satellite populations in situ and establishing a single third population on Floreana using birds from both islets to maximise genetic diversity upon which selection can act.