Seabird sampling effort within the Chagos Archipelago and the British Indian Ocean Territory. Boundaries of the BIOT MPA (a), and locations within the Indian Ocean (inset). Individual atolls and islands (b-g). Black dots represent the location of individual bird transects. Rat-invaded islands are coloured in red and rat-free islands in blue. Six islands have been reported with uncertain rat status (Île Verte, Île Manon, Île Finon, Île de la Passe and a small Unnamed Island in Peros Banhos) and are for representation purposes shown as rat-invaded.