June 28, 2000.
How the Galapagos Islands Saved Giant Tortoises From All But Humans
This is Roger Payne speaking to you from the Odyssey, as we sail among the Galapagos Islands.
I have several times referred to the giant tortoises of these islands. As I have said it is believed that the first ones probably reached the Galapagos by floating in on currents from South America, carried in their own shells, or riding on mats of floating vegetation. The trip would only take about three weeks and there would be no danger of starvation-whalers stocked their ships with tortoises for fresh meat, storing them in their holds for up to a year with neither food nor water.
From the first individuals that arrived, 14 species and subspecies evolved, each adapted to its own island environment. Tortoises live mostly in the volcanic craters of their respective islands. Their shell varies in size and shape from one island to the next. Giant tortoises can weigh up to an astonishing 270 kg. Great size is often coupled with longevity and this is true for giant tortoises. It takes them 25?30 years to reach sexual maturity and they may live for as long as 150 years. This means that some individuals may even have encountered Darwin himself.
Though it might seem disastrous for the giant tortoises that floated out to the Galapagos, that undoubtedly harrowing trip saved their species. Their continental ancestors eventually died off, victims, presumably, of bigger and better predators, or of egg robbers, until finally their descendants in the Galapagos were the only survivors. Terrestrial mammals, being warm blooded, are not as well adapted as tortoises for crossing large expanses of water, so for millennia the Galapagos hawk was the only threat to giant tortoises, and then only to hatchlings. However, when humans came they introduced goats, pigs, donkeys, dogs and rats, species that compete for grazing, damage nests, eat eggs and young, and change forest habitat to grassland. The result was that the number of tortoises went from perhaps 200,000 to 15,000 individuals, a population loss of 92%.
When people discovered these islands there were 14 species and subspecies of tortoises here. Since that time three subspecies have been lost, and only a single individual represents another. Affectionately known as 'Lonesome George', he is the last of the Pinta island giant tortoises. The Charles Darwin Research Station and the Galapagos National Parks Service have intensive efforts underway, including breeding and reintroduction programs, with which they are attempting to restore endangered tortoise populations. The Galapagos Islands may have saved the giant tortoises of South America, but in spite of our best efforts, it is we who now threaten them. These efforts have come too late for Lonesome George. In spite of intensive searching, no one has been able to find a mate for him. He is living out his last days (and the last days of his species) in his own pen at the Charles Darwin Research Station.
To look him in the eye is to stare extinction in the face.
That's all for now, that's more next time.
© 2000 - Roger Payne