Smithsonian.com

Invasive brown and black rats feed on the eggs of the Galapagos land iguana. Photo: Nicolas de Camaret

When a young Charles Darwin first set sight on the Galapagos Islands on September 15, 1835, he already had an inkling that the rocky equatorial Pacific archipelago would be a good site to study the effects of geography on biology. The classic emblem of Darwin’s theory of natural selection are the Galapagos Islands’ many and varied finches, each with a beak well-suited to the food source it has on offer.

Due to their relative isolation, many of the species living on the Galapagos Islands are quite unique in the world—a rarity that has put a huge swath of the Islands’ endemic species on the extinction watch-list. Through centuries of travel to-and-from the Islands, people have aided in this race towards extinction by introducing a number of competitive non-native species, two of the most prolific being the brown and black rats. The Associated Press:

The invasive Norway and black rats, introduced by whalers and buccaneers beginning in the 17th century, feed on the eggs and hatchlings of the islands’ native species, which include giant tortoises, lava lizards, snakes, hawks and iguanas. Rats also have depleted plants on which native species feed.

The rats have critically endangered bird species on the 19-island cluster 1,000 kilometres from Ecuador’s coast.

In the second leg of a project kicked off last year, Ecuadorian officials are set to drop 22 tons of poisoned pellets onto two of the Galapagos Islands over the coming weeks in a bid to wipe out 180 million rats.

Those who paid attention in high school biology classes, the idea of swooping in and systematically restructuring the local ecosystem may seem like a risky measure. But, says The Guardian:

While some may be appalled at the thought of deliberately dumping toxins in one of the most biodiverse and pristine places in the world, conservationists say risks have been minimised to ensure this is the lesser of evils.

“The rats cause a great deal more damage than the poison,” said Linda Cayot, science adviser for Galápagos Conservancy. “They have decimated 100% of tortoise hatchlings for the past 100 years.”

In advance of this operation, she said, years of research has gone into lessen the impact on other species.

… ”No one likes to see the extermination of large numbers of animals, but it is either the rats or the tortoises and iguanas,” said Scott Henderson of Conservation International. “Any conservation measure entails a measure of risk, but in this case the risks are low and carefully calculated.”

More from Smithsonian.com:

The Beautiful and Bizarre Galapagos Islands
When It’s Okay to Kill 80,000 Wild Goats
The Last of His Kind, Tortoise Lonesome George Dies, Leaving No Offspring