Breeding biology of the Critically Endangered Galapagos Petrel Pterodroma phaeopygia on San Cristóbal Island: conservation and management implications

The Galapagos Petrel Pterodroma phaeopygia is endemic to the Galapagos Archipelago, where it nests on only five islands. The species is considered ‘Critically Endangered’, mostly due to the effects of alien invasive species, which impair its reproductive success. During 2002–2003 we studied the breeding biology of the petrels nesting on San Cristobal island. The study revealed particular characteristics of the San Cristobal petrel population and differences compared to those of other islands, mostly related to nesting habitat, phenology, reproductive success and causes of mortality. On San Cristobal, petrel nests were primarily located along ravines, in areas of dense vegetation cover formed by the endemic shrub Miconia robinsoniana and a wide variety of native ferns. Over 90% of the nests on the island were located on private agricultural land. The petrel population has a prolonged reproductive period covering 10 months. Laying dates occurred mostly from May to October, with a peak during August, although eggs may be occasionally laid between November and March. The incubation period averaged 50.8 days (range: 46–53), and parental care 103.7 days (range: 98–108). Overall reproductive success was 23.6%; 63.8% for eggs and 37.1% for chicks. Predation by rats was the primary cause (72.2%) of nest failure. Rat control campaigns and clearing of exotic plant species in areas of high density of petrel nests, as well as promoting cooperation agreements between conservation authorities and landowners of the properties where nests are located, are suggested among other critical management measures intended to reduce nest mortality and ensure the survival of the San Cristobal petrel population.