Endangered Peruvian diving petrels were once common on coastal islands off of Peru and Chile, but species introductions have reduced populations throughout their former range. For example, over 100,000 pairs were extirpated on a single Chilean island after the introduction of foxes in the mid-1900s. Meanwhile, the current total population estimates range within the tens of thousands and breeding occurs on only four islands, with the largest concentration believed to be at Isla Choros, Chile. Understanding the breeding biology of this little-studied species is important for helping to conserve remaining populations; however, this project was particularly timely in that the removal of European rabbits is planned for a set of islands in Chile to promote the recovery of Humboldt penguins and Peruvian diving petrels. The opportunity allows for taking advantage of this conservation measure as an experiment to determine the impact of removing an introduced species on the ecology of the islands themselves and the population dynamics of seabirds. The primary objective of the study was to conduct surveys to characterize the breeding biology of Peruvian diving petrels on Choros Island prior to the removal of rabbits, against which the recovery of the petrel populations can be assessed.
Surveys of Choros Island identified 19 Peruvian diving petrel colonies with an estimated 10,032 nests, of which 3,611 were estimated to be occupied (suggesting approximately 7,000 breeding pairs). These are the first such data available for this species on this island, and suggest that burrow availability is not a limiting factor for population recovery. Researchers also tracked segments of the reproductive cycle, documenting for the first time that chicks are present as early as November (unexpectedly early for this family of seabirds in this region of the world) and that the majority of chicks have fledged by March. In addition, surveys were conducted on introduced European rabbits, which compete for and destroy petrel burrows; burrowing owls, which are native predators of petrels; and plant cover, which affect erosion, soil stability and suitability of burrowing habitat. Collectively, this information provides important basic biological information and will be invaluable for comparison once eradication efforts are implemented. ($10,000)