Guest blog – Invasive black rats in Galapagos by James Fage

Our guest blog has been kindly written by James Fage, a recent graduate in Biological Sciences

Black rats and brown rats are major conservation threats to islands worldwide, and Galapagos is no exception. Black rats first reached the Galapagos Islands in the holds and living spaces of visiting pirate and trade ships, just after first European contact in the 17th century. Brown rats were initially seen in major ports of Galapagos in the 1980s and rapidly spread. As of 1985, over 80% of all islands globally had been invaded by rats.

Predation and decimation

The impact of rats is particularly severe in Galapagos due to the high numbers of endemic species – plants and animals found nowhere else. Many island species have evolved in the absence of predators; native birds breeding in the Archipelago are often ground nesting. Therefore, eggs and young hatchlings are particularly vulnerable to new predators. Due to this influx of alien predators, several of the Islands’ unique bird species have become critically endangered. Egg predation by rats also affects reptiles. In the 1960s, conservationists on the island of Pinzon noticed that all the giant tortoises they saw were almost a century old. Due to invasive rats, not a single young tortoise had survived the egg or hatchling stage for several decades.

Invasive rats also threaten the Islands’ own species of rice rats, namely, the small and large Fernandina rice rats, the Santiago rice rat, and the Santa Fe rice rat, each restricted to a single island. Of these, the Santiago rice rat is the only one to survive competition with invasive rats, as the latter are absent on Fernandina and Santa Fe. Three other rice rat species have already been driven to extinction by both direct competition with black rats, and by the diseases they carry.

Invasive black rat © Ian Dunn

Project Pinzon

Despite the considerable harm caused by invasive rats, however, things started to look more hopeful in 2007 with the start of Project Pinzon. This ambitious initiative aimed to successively clear rats from North Seymour Island, Rabida, and Pinzon (plus many other smaller islands) by dropping poisoned rat bait from helicopters. Early tests showed no major risks to other animals, but nobody took any chances – a small population of tortoises from the targeted islands was taken into captivity just in case. 2012 saw the final phase of this project on Pinzon, with 45 tonnes of bait dropped over 18 square kilometres. It was a success – Pinzon, Rabida, and North Seymour are now all rat-free. Furthermore, in December 2014, the first new giant tortoise hatchlings were seen for more than a century. On the cleared islands, populations of reptiles and seabirds, including the Galapagos petrel, have already started to increase. Careful and frequent monitoring is needed to ensure that rats do not return, as there is always a risk black rats could be reintroduced to these islands by boat.

Project Pinzon was so successful that it has now been extended into its fourth phase – Project Floreana. Previous rat eradication attempts have focused on remote, mostly uninhabited islands. Floreana will certainly provide unprecedented challenges, with its human population and 173 square kilometre area. Work on Floreana is ongoing, but, if successful, would set a shining example to the rest of the world of what conservation can achieve.

If you would like to learn more about and donate to the work in Floreana, please click here.