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  Page updated:29.06.2009

Eradication, monitoring, and control of introduced rats (Rattus rattus and Rattus norvegicus)

For more information contact:
Víctor Carrión, +593 (0)5 252 6189 Ext. 145, vcarrion@spng.org.ec

The black rat was most probably introduced by boats.

Rodents are carriers of many diseases that infect humans and other animals. In the Galapagos Islands, introduced rats were probably brought by pirate and buccaneer ships in the late seventeenth century and sporadically by subsequent colonization. 

Rodents have caused problems, primarily in planted fields, and have transmitted diseases to humans and other animals for thousands of years.

Rodents are carriers of many diseases that affect humans and other animals, caused by ectoparasites (fleas, ticks), viruses (hantavirus), bacteria (Salmonella spp., Leptospira spp.), and protozoa (Toxoplasma gondii), among others. Other more common diseases include intestinal infections; toxoplasmosis, whose effects cause eye and brain damage in adults and fetuses; and salmonellosis, which causes high fevers, body aches, diarrhea, and sometimes meningitis.

Rodent control is the best remedy to control these pests, mainly on oceanic islands like the Galapagos that are vulnerable to the introduction of new diseases. Also, its unique flora and fauna are affected. In some cases rodents have caused the extinction of several animal species.

Endemic rodents of the Galapagos

Introduced rats are also a threat to the endemic rodents of the Galapagos.

The mouse endemic to Santiago (Nesoryzomys swarthi).

The last endemic mouse on Santa Cruz (Nesoryzomys indefessus) was captured in 1934. Their extinction was most likely due to the introduced black rat, by spreading diseases and/or by competing for space and food, as well as by the feral cats on the island.

The mouse endemic to Santiago (Nesoryzomys swarthi) was believed to be extinct for the same reasons, as it had not been seen since 1906, but was rediscovered in 1997.

Something similar happened with the mouse endemic to Fernandina (Nesoryzomys narboroughi), that was recently rediscovered.

Both are very vulnerable to predatory introduced species, so it is essential to carry out continued monitoring and strengthen the rat and cat eradication operations on these islands.

Advances in the control and eradication of rats

Introduced rats are a problem in populated areas and protected natural areas.

In 2007, thanks to support from several worldwide organizations and particularly the Charles Darwin Foundation, an international workshop on Santa Cruz Island was organized with the participation of experts in rodent management from all over the world.

This event resulted in the Regional Strategy for the Management of Rodents in the Galapagos Islands.

One of the first actions taken as a result of the recommendations of the document, was the eradication of rats on North Seymour, Island, where monitoring after the implementation of the control product has not indicated the presence of rodents. In any case, the monitoring efforts must be maintained to detect possible survivors and proceed with their early elimination.

Current work and future challenges

By eradicating cats from Baltra Island the introduced rat population has increased considerably, reason for which a rat control program is being implemented, at least in the populated areas of the island.

Another action that is being performed on the Islands, is the monitoring of visitor sites and islands where rodents have not yet been introduced, or where they have been eradicated: Fernandina, the Bainbridge islets, the Marielas Islands, Santa Fe Island, and Española.

» Introduced rats in Galapagos

In 2009 the rodent monitoring work began on Pinzon and Rabida islands. This work will be executed jointly with the Charles Darwin Foundation. The idea is to determine the types of rodents present on the two islands, determine the approximate concentration of the population, and experiment with the use of non-toxic baits with non target species such as turtles, marine iguanas, or sparrowhawks.

Given the climatic conditions of 2009, (this is a dry year and this causes a drastic reduction in rodents, due to lack of food in particular) steps are being taken to implement eradication actions this year.

Also in collaboration with the Charles Darwin Foundation, the monitoring of the mangrove finch population continues in Caleta Tortuga Negra, Caleta Black, and Bahía Cartago on Isabela Island. This work contemplates the monitoring and control of rats, to prevent this introduced species from predating upon a population as small as the mangrove finch population (about 48 individuals!). 

On the islands of San Cristóbal and Santa Cruz, the Directorate of the Galapagos National Park, in conjunction with the CIMEI, carries out rat control programs in the urban and agricultural areas of these islands.

In urban areas periodic monitoring and control campaigns are carried out in public places, where bait stations are used to estimate the population density and control rodents.

Rat control programs are also carried out in protected areas corresponding to the nesting sites of the petrels.

This program has counted on the support of:

The Charles Darwin Foundation for the Galapagos Islands (CDF) is an international nonprofit research organization dedicated to providing scientific research, technical assistance and information in order to ensure the success of conservation in Galapagos.


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