San José, Costa Rica, since 1956

Rats Invade Isla del Coco

Isla del Coco, declared a World Natural Heritage Site by the United Nations in 1997, has been invaded by rodents – hundreds of thousands of them.

According to a recent study by Juan Ricardo Gómez, a student at the National Institute for Wildlife Conservation and Management, part of the National University (UNA), many of the unique species that inhabit the island could disappear if the estimated 210,000 rats are not eradicated.

The rats aren’t native to the island, which, thanks to its isolated location 600 kilometers off the coast of Costa Rica, has evolved a large number of endemic species, much like the Ecuador’s Galapagos Islands.

Gómez estimates current rat populations at over 87 per square hectare – and because they are omnivores, they eat all manner of native vegetation, birds, insects and reptiles.

The study indicates that rats pose a serious risk to native wildlife, either by competition for food sources or direct predation. The exact date of arrival of the rats is unknown, though most believe they were transferred by boat, most likely by accident, according to Gómez.

Fernando Brenes, director of the Isla del Coco Marine Conservation Area, believes that the rats and other invasive species, including pigs, deer, cats and goats – all introduced to the island in the last two centuries – must be eliminated, but care must be taken to not harm native species in the process.

“The state must do what it can to safeguard the native species here,” he said, while acknowledging that the costs and man-hours associated with such a project could be prohibitively high.


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