Rats and prions at Tristan da Cunha Island

Abstract

Tristan da Cunha is a 96 km² volcanic island in the South Atlantic Ocean. Black Rats Rattus rattus reached the island from a shipwreck in 1882 and their depredation of seabirds’ eggs and chicks are likely partly responsible for the much lower densities of burrow-nesting petrels, compared with adjacent rodent-free islands in the archipelago. We monitored a colony of Broad-billed Prions Pachyptila vittata breeding in a coastal cliff cave in 2015/2016, where a maximum of 6% of chicks survived from 310 nests. We suspect rats frequently depredated eggs (36% of eggs were found broken with rat bite marks) and infrared trail cameras recorded how rats repeatedly hassled chicks, although no direct chick depredations were recorded.