Evaluating black rat eradications on islands in the Gulf of California, Mexico

Techniques for eradicating rodents from islands have experienced a significant development during the last decades, achieving success on around 300 islands worldwide. Aerial broadcast techniques facilitate eradication on big and complex islands. However, it remains difficult to confirm success. Failure is assessed by waiting until such time as survivors could have produced enough offspring for the population to become easily detectable, which usually means two years of intensive post-eradication monitoring. Moreover, the effort and cost involved may be even higher than the eradication itself. We examine the case of the aerial rat eradication on Farallón de San Ignacio and San Pedro Mártir islands in the Gulf of California, México, in fall 2007. Confirmation of the eradication is an ongoing task on these islands. We discuss the cost-benefit tradeoffs of implementing additional detection studies and conducting spatial simulations to improve the assessment of eradication success.