To save a mockingbird

A mockingbird that sowed the seeds of evolution in the mind of Charles Darwin stands on the precipice of extinction, with no more than about 100 breeding pairs left alive in its home on the enchanted Pacific islands of the Galapagos Archipelago.

The Floreana mockingbird is the unsung hero in the story of evolution. It played a pivotal role by making Darwin realise that species were not stable units but changing entities subject to the vagaries of competition and the forces of natural selection. It went extinct on its home island of Floreana in the Galapagos within a few decades of it being discovered by Darwin, because of the introduction of rats, pigs and feral cats, and now survives in two small, isolated populations on the nearby satellite islets of Champion and Gardner-by-Floreana. Scientists believe those remnant colonies are so small and inbred that they could soon disappear with the next drought or famine, which is why the species was placed on the critically endangered "red list" of the International Union for the Conservation of Nature this year.

But now a team of researchers and conservationists has devised a bold plan to reintroduce the blackbird-sized birds back to the bigger island of Floreana in the hope of building up the population to the many thousands of individuals that cheekily greeted Darwin on his arrival there in 1835 – one of them audaciously drank from a cup of water he was holding in his hand.

Intriguingly, an essential element of this reintroduction initiative has centred on a dried museum specimen of the Floreana mockingbird, as well as one from the nearby island of San Cristobal that Darwin himself brought back to Britain from his five-year voyage on HMS Beagle, during which he collected the thousands of biological specimens that inspired his 1859 book, The Origin of Species.

Scientists have extracted DNA from the fleshy foot pad of the Floreana specimen, which is to go on display at the Natural History Museum in London next week, to gauge the level of genetic diversity that may have existed within the original population on the island.

They are using the results to compare the genetic makeup of the specimen against the DNA extracted from blood samples taken from individuals living on the islands of Champion and Gardner. The hope is to identify those birds that will be best suited to act as breeding pairs when building up a new colony on Floreana.

"For most projects involving the reintroduction of animals it is important to maximise the genetic diversity to prevent or limit inbreeding," said Karen James, a researcher at the Natural History Museum who is involved in the reintroduction programme.

"We can use these results of the DNA analysis to select the right birds for reintroduction. The aim is to see if it is possible to breed them in captivity before releasing them into the wild on Floreana where we hope they would become established," Dr James said.

The importance of the Galapagos mockingbirds to the story of evolution cannot be overestimated. Darwin had travelled about 4,000 miles along the South American coast and had seen just three species of mockingbird during that time.

And yet, when he journeyed from the Galapagos island of San Cristobal to Floreana, just 50 miles away, he found two quite different mockingbirds with as many distinct differences between them as there were with the mockingbird species he had seen on the mainland of Chile.

When he had left the Galapagos on his three-week voyage to Tahiti he had time to inspect his specimens more closely. It was then that it dawned on him that the two mockingbirds of San Cristobal and Floreana, separated by just 50 miles of water, were probably separate species unique to each island.

"Each variety is constant in its own Island," Darwin wrote in his notes prepared during that part of the voyage in October 1835. Later on in his life, Darwin was to note that the four different species of mockingbird on the islands of the Galapagos illustrated how competition and natural selection could result in the evolution of one species into another.

"Darwin's first sightings of the Galapagos mockingbirds were to prove historic," said Randal Keynes, a Darwin scholar who also happens to be the great-great-grandson of the founder of the theory of evolution by natural selection. "He later noted in The Voyage of the Beagle that the small difference between the mockingbirds on the two islands was a 'most remarkable fact in the distribution of organic beings'. Darwin had come to understand that species can change and this ultimately led to our present understanding of life on Earth," Mr Keynes said.

"There wasn't a blinding 'Eureka' moment. The idea crept up on him, and because of the way he recorded everything, we can see pretty clearly with the mockingbirds what he recognised, and when. This bird is the single most important species in the history of science," he said.

Tradition has it that it was the finches of the Galapagos that inspired Darwin to come up with the concept of evolution by natural selection. But in fact the finch specimens he collected were badly mixed up and he had failed to make a note of which island each specimen had originated – an "inexplicable confusion", he wrote. However, things were different with the mockingbirds. Darwin had already been primed with his experience of mockingbirds on the South American mainland, so it came as something of a shock to him to find two quite distinct varieties living on the two islands of the Galapagos that he visited first – San Cristobal and Floreana.

"There are five large islands in this Archipelago, and several smaller ones. I fortunately happened to observe, that the specimens which I collected in the two first islands we visited, differed from each other, and this made me pay particular attention to their collection," Darwin wrote. "The fact, that islands in sight of each other, should thus possess peculiar species, would be scarcely credible, if it were not supported by some others of an analogous nature, which I have mentioned in my Journal of the voyage of the Beagle."

The mockingbirds were just one example of "adaptive radiation" – when one species can evolve into several after it arrives in a new, unexploited habitat – which occurred for instance when a mainland species of finch arrived for the first time in the Galapagos.

Darwin was also to observe another feature of evolution – when isolated populations evolve unique characteristics, so-called island endemism. The Galapagos produced fine examples of this, from daisy-like plants that had evolved into trees, to giant tortoises that were unique to each island.

"The point about the two mockingbirds he had collected from San Cristobal and Floreana was that they made him realise that they were two distinct species, from two different islands. The key point is that they raised the possibility of speciation – the creation of new species," Mr Keynes said. "In the sense that you can trace all of Darwin's further thinking towards the understanding that species may change and that they change by natural selection, the mockingbirds were important. They alerted him to the possibility that species might change."

Conservationists believe that the island of Floreana has never in more than a century been more hospitable for the reintroduction of its famous mockingbird.

Many of the feral animals introduced over the years have been culled or eradicated, so much so that on part of the island, ground-nesting petrels have returned to breed after decades of being persecuted by egg-thieving rats.

High rainfall on the islands in recent years had led to a relative boom in the mockingbird populations on Champion and Gardner, which had raised hope that it would be possible to take some of the birds back to Floreana for breeding, said Paquita Hoeck, of Zurich University, who is carrying out the research as part of her doctoral thesis.

"They have been doing relatively well so far but the two isolated populations are inbred and their overall numbers are still low, so they are still in a very dangerous situation," Ms Hoeck said.

"We needed to look at the DNA of the historic specimen kept by the Natural History Museum in London because it is the only specimen that can indicate the genetic make-up of the original population on Floreana at the time of Darwin," she said.

"We are using this to compare against the DNA of living birds that we hope to use for breeding in the reintroduction programme."

But funds are still needed, which is why the Galapagos Conservation Trust and the Charles Darwin Foundation have launched an appeal to raise £60,000 for the reintroduction programme to begin next year, the bicentenary of Darwin's birth.

Toni Darton, the chief executive of the trust, said that it would be a tragedy if the bird that did so much to inspire Darwin was to go extinct 200 years after he was born.

"Although Darwin's finches previously received the credit for inspiring his radical thinking on the evolution of species through natural selection, actually this honour belongs to the mockingbird," Ms Darton said.

Switch your Gas & Electricity and save up to £380 with Independent Compare