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November 20th, 2012
On Wednesday afternoon, Galapagos National Park Service (GNPS) rangers and partners from Island Conservation began to spread rodent bait on South Plaza Island, and later moved the operation to Pinzón Island, where they had completed the first application on Saturday.
Introduced black rats have prevented the giant tortoises on Pinzón Island from successfully reproducing in the wild for nearly 150 years, due to their predation on tortoise eggs and hatchlings. For the past 45 years, the GNPS and Charles Darwin Foundation have collected eggs, and artificially incubated, hatched, and raised the young in captivity. At four years of age, the young are considered “resistant” to attack by rodents and can be returned to their natural habitat. Since the first reintroduction of 20 young Pinzón tortoises in 1970, more than 550 juvenile tortoises have been released on the island. The rodent bait used in the project does not pose a risk to the tortoises.
The Galapagos National Park Director, Edwin Naula, said, “Invasive species are recognized as a major threat to the biodiversity of Galapagos, so the National Park Service and its partners are using new techniques to remove these threats and to prevent the extinction of species not found anywhere else in the world, such as the giant tortoise of Pinzón.”
Invasive rats also have had negative effects on the endemic Pinzon lava lizard, resulting in the decline of this unique species. On South Plaza Island, invasive mice destroy the root systems of the Opuntia cacti, a favorite food of Galapagos land iguanas and other endemic species such as the cactus finch.
On the Use of Rodenticides
The GNPS has received many inquiries regarding the risks of using anticoagulant rodenticides in protected areas. Before implementing eradication programs, the Park and its partners conduct thorough toxicity studies involving the species found on each of the islands where baits are to be applied in order to determine which species are at high, medium, or low risk. Mitigation plans have been implemented for such species as the Galapagos hawk, which are being kept in captivity for as long as the bait is considered toxic in order to protect them from primary exposure (by eating the bait) or secondary exposure (indirect contact from eating dead or live animals that have been poisoned).
Other tests were performed before the eradication, in order to determine whether it was necessary to modify the existing bait formulas to increase their effectiveness and/or to reduce their attraction of non-target species.
Removing introduced rodents from the islands is extremely important for the ecological restoration of Galapagos ecosystems, which still retain 95% of their original flora and fauna despite the presence of introduced species.