The San Jorge Islands are in the northern part of the Sea of Cortez in Mexico. They consist of three islands each infested by Black Rats, Rattus rattus, which prey on seabird eggs and nestlings. In addition to ridding the island of rats and restoring bird populations, this project was scientifically important for its comparison of three different rodenticides.

Isla San Jorge, Mexico

The islands of northwest Mexico are largely (90%) publicly owned and part of the national system of nature reserves and there is increasing public support for their conservation. The three San Jorge Islands are part of the Biosphere Reserve and are home to six species of threatened seabirds – Least Storm-Petrel, Black Storm-Petrel, Craveri’s Murrelet, Heerman’s Gull, Yellow-footed Gull and Red-billed Tropicbird. Predation by introduced rats had dramatically reduced the nesting success and even adult survivorship of these and other species.

The grantee, Santa Cruz, CA-based Island Conservation, collaborated with the FIF Chairman Dick Spight and Mexico’s Grupo de Ecologia y Conservaciónde Islas to:

• Eradicate the introduced rats from the islands.
• Test the efficacy of two new rodenticides, and compare them with the conventional rodenticide.
• Provide technical training to workers and managers in the Reserve and some private groups through participatory field work.

Red-billed Tropicbird

The conventional rodenticide is known to be effective but can cause some secondary and non-target poisoning. The experimental rodenticides had not been field tested but were known to have little secondary or non-target toxicity. If either proved equal to or superior to the conventional rotendicide in this small island study, it would then be adopted for use on larger islands. The eradication of rats requires that every rat be eliminated.

This research found that the conventional rodenticide achieved this goal while the experimental ones achieved less than 100% elimination. (Donlan CJ, Howald GR, Tershy BR, Croll DA (2002). Evaluating alternative rodenticides for island conservation: roof rat eradication from the San Jorge Islands, Mexico. Biological Conservation).