This is a continuation of a 2010 CREOi-funded project. The Peruvian diving petrel (Pelecanoides garnotii) (IUCN Endangered) was once very common on coastal islands of Peru and Chile. However, guano mining and the introduction of invasive species have caused declines in breeding populations throughout their original range. In Chile, most of the population is found on Isla Choros, including 94% of breeding individuals. The island is characterized by an abundance of native and endemic flora; however, it has been subject to the introduction of invasive species, most notably the European rabbit Oryctolagus cuniculus and the plant Mesembryanthemum cristallinum. The rabbits are well-known for destroying or occupying seabird burrows during the nesting season. Rabbit foraging pressure has also reduced native vegetation cover, exposing the soil to erosion and leading to the rapid expansion of the invasive M. cristallinum.
This project included the long-term (2010-2015) monitoring of breeding petrel density and plant cover diversity on Isla Choros. During July and August of 2013, European rabbits were successfully eradicated from Isla Choros by the Chilean National Forest Service (CONAF). This allowed for an integrated assessment of ecosystem elements pre- and post-eradication of rabbits. The effects of the eradication were measured on petrel breeding density and physiological condition, as well as the plant community. The results suggest that among the petrel population variables measured (nest density, number of active breeding pairs, plant diversity, plant cover), only the number of active breeding pairs was significantly different before and after rabbit eradication. The physiological condition of petrel chicks was significantly better after rabbit eradication, though this could be due to factors such as the availability of prey at sea or the level of parental experience over the course of the breeding seasons studied.
Although there were no statistically significant differences in plant cover, it is notable that after the eradication there were new plant species that had not been previously observed on the island during the study period. Finally, the results of this work have been made available to CONAF through reports, presentations and participatory workshops, which have been very successful for communicating technical and scientific information to decision-makers. This is reflected in the fact that CONAF is now supporting continued post-eradication monitoring of the Isla Choros ecosystem. ($8,000)