Population census and nesting habitat selection of thin-billed prion Pachyptila belcheri on New Island, Falkland Islands

Catry, Paulo; Campos, Ana R.; Segurado, Pedro; Silva, Mónica C.; Strange, Ian J.

http://hdl.handle.net/10400.12/1506

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Abstract(s)

Seabirds have the potential to be used as indicators for monitoring changes in the southern oceans. However, many species and populations are still poorly known. The thin-billed prion (Pachyptila belcheri) is the most abundant seabird species around the Falkland Islands, but this far, no detailed censuses of its populations had been carried out. In this study, we developed a methodology, based on standard field methods combined with a Geographical Information System, to census the biggest known colony (New Island) of this species. Data were also collected on nesting habitat preferences. Results indicate that there are 1,081,000 (95% confidence limits: 815,000–1,346,000) apparently active nest-burrow entrances on New Island South which, given the very high occupancy rates by known breeders, should correspond to a similar number of nesting couples. We present quantitative evidence that this result can be extrapolated for the entire island, giving an overall estimate of 2 million pairs. Prions have an almost ubiquitous distribution on New Island, but they are more frequent in areas with steeper slopes (excluding cliffs). Habitats dominated by introduced grass species generally hold higher densities of nests in comparison to most native formations.