With the objective of reducing the negative impact produced by the cats and restore a Galapagos ecosystem, the Galapagos National Park (GNP), with technical support from the Charles Darwin Foundation (CDF), began a project with the principal objectives of eradicating cats from Baltra island, and the restoration of its natural habitat. In addition, the project guarantees the survival of a population of repatriated land iguanas Conolophus subcristatus, a species made extinct on this island in the past, partly due to the presence of feral cats.
Eradication of cats was possible for various reasons: firstly, it is an island with a very small human population and therefore with a low risk or re-introduction of cats; its size is small (26km2) which helps control and monitoring; and lastly, the vegetation is sparse, with many open areas.
Studies on feral cat behaviour and the most appropriate methods of control revealed that cats are active during the day and night. During the day, GNP staff looked for tracks and signs, and placed traps (Tomahawk and Victor types) and poison. At night, hunters removed cats with spotlights and rifles. With the objective of ensuring total eradication, in 2001, sodium monofluoroacetate (1080) in fish baits was placed over the entire island. The island was divided into 13 sectors and 350 bait stations were placed.
This methodology was successful in controlling the cats. The population has slowly been reduced to the point of eradication. Removal of the remaining cats was complicated by a weather-induced eruption of rats Rattus rattus, and mice Mus musculus, that enabled recruitment of kittens in 2002, but made cats more sucseptible to trapping and shooting in 2003 when the rodent population collapsed. By the end of 2003 no sign of a cat was seen on Baltra despite extensive searching.
Periodic monitoring on Baltra continues throughout 2004 to confirm the eradication of the feral cats, and the establishment of colonies of repatriated land iguanas.
On reduction of the cat population there have been immediate increases in the numbers of locally bred terrestrial iguanas seen during annual censuses. However, this response may reflect the coincidental maturation of young produced by iguanas repatriated from 1991 onwards or climatic variations rather than resulting from reduced cat predation alone. It may be necessary to wait some years to see the full benefits of reduced cat predation.
Currently the GNP is carrying out cat control programmes at two sites, Cerro Dragon and Cerro Montura, on another island in Galapagos, Santa Cruz. In addition, they are monitoring other islands to determine the areas where feral cats are threatening native species.
Source: Galapagos National Park and the Charles Darwin Foundation.