Evidence of breeding White-faced Storm-petrel Pelagodroma marina on St Helena Island, South Atlantic: vagrancy or a relict from human pre- colonisation?

Abstract

During an overnight ringing expedition to the Oceanodroma storm-petrel colony on Egg Island, St Helena in July 2009, a White-faced Storm-petrel Pelagodroma marina was found on the ground under an open mist net. The bird was easily captured and close examination in the hand, together with subsequent inspection of photographs, showed that the bird was recently fledged. Biometrics and timing of fledging preclude provenance from the closest colony on the Tristan da Cunha archipelago and the pristine nature of the plumage render an origin from the northerly colonies of Cape Verde or the Selvagens Islands, around 4,000 km distant, unlikely. We suggest this bird probably fledged locally, quite possibly on Egg Island itself, where the substratum is suitable for burrowing. The length of the bird’s tarsus was within the range of sub-fossil specimens from St Helena, which show the species was once widespread and abundant there. This recently-fledged individual raises the possibility that a relict population may persist on one or more of the predator-free offshore stacks that surround the St Helena mainland.