The Tropicbirds Phaethon spp. of the Islas Desventuradas Archipelago, Chile

We found nesting Red-billed and Red-tailed tropicbirds Phaethon aethereus and P. rubricauda in the Islas Desventuradas archipelago, Chile. We visited Islote González on 14–15 December 2020 and on 23 August 2021. During the December visit, we encountered a colony of Red-billed Tropicbirds totaling a minimum of 62 breeding pairs. The nests were in cavities on steep cliffs and slopes located mainly on the northern part of the island, and we were able to access 34, of which 11 had eggs, 11 had nestlings of different ages, and 12 were active but empty. During the August visit, we found four nests with adults attending but no eggs or nestlings, one nest with a chick close to fledging, and one adult attempting to take a nest site from a De Filippi’s Petrel Pterodroma defilippiana. We visited San Ambrosio Island on 10–12 December 2019, and we found only the Red-tailed Tropicbird breeding, as evidenced by four active nests: two with eggs, one with a well-grown nestling, and one with a pair of adults but no nest contents. However, we observed several pairs in aerial display and estimated the Red-tailed Tropicbird population to be at least 10–12 breeding pairs, in addition to the five to six pairs at Islote González and about eight pairs at San Félix Island. Our findings represent a new Red-billed Tropicbird population and the largest breeding colony of the species for Chile. Furthermore, Islote González is one of the very few known places where sympatric breeding of Red-billed and Red-tailed tropicbirds occur. The White-tailed Tropicbird Phaethon lepturus is also known to nest at San Félix Island in the Desventuradas archipelago, but we did not visit that island. It appears that all three species of tropicbird nest in this archipelago.