Abstract

Anthropogenic impact has been heavy in remote oceanic islands, including the introduction of alien species, having negative effects on native seabirds. The isolated and subtropical Rapa Nui (Easter Island) is one of the few known breeding sites of the red-tailed tropicbird, Phaethon rubricauda in Chile (southeastern Pacific Ocean) where is listed as vulnerable. A relatively new breeding colony is found in the Rano Raraku volcano, where human-introduced species are present. We used hen eggs as a proxy for red-tailed tropicbird eggs to assess potential predation risk on unattended eggs. Each experimental egg was monitored by camera traps during 6 days. Three predatory species were identified on the records: the Brown rat Rattus norvegicus, the Polynesian rat Rattus exulans, and the raptor Chimango Caracara Phalcoboenus chimango. The most frequent species were the Rattus spp. A total of 45 predatory visits were recorded with a total time of 1.7 h, accounting for the 0.3% of the experimental time. Within this time of visits, all the potential predators spent time in both interacting activities (trying to prey on) and no-interacting activities with the experimental eggs. Only a Brown rat was able to prey on one of the eggs. Our results suggest that these invasive species are a low threat for unattended red-tailed tropicbird eggs at Rano Raraku, Rapa Nui. However, future research is needed to determine the potential negative effects over unattended red-tailed tropicbird nestlings that are easier for these predators to handle compared with an egg.