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Introduction
Procellariiforme seabirds (albatrosses, petrels and shearwaters) are becoming threatened at a faster rate globally than any other bird order (BirdLife International 2008, Croxall et al. 2012), with 45% of extant taxa currently threatened (IUCN 2010). The primary drivers of this decline are twofold: the impacts of invasive alien species at nesting sites, and the operation of commercial longline fisheries within seabird foraging areas (Butchart et al. 2004). Governments and non-governmental organisations around the globe are attempting to redress this situation. A number of national and international threat abatement plans have been developed and are currently being implemented along with various species recovery plans. Despite these efforts many threatened seabirds continue to decline, with few species having increased in abundance. The Bermuda Petrel (or Cahow) Pterodroma cahow, endemic to the islands of Bermuda (32°20'N, 64°45'W; 53 km2) in the western North Atlantic Ocean, is an 'Endangered' species (IUCN 2010) whose population has increased greatly in number in response to recovery actions.
Subfossil evidence suggests that when the Bermuda archipelago was first discovered, early in the 16th century, the Bermuda Petrel was widespread and abundant (Shufeldt 1916). Spanish mariners introduced pigs to Bermuda around 1560 (Lefroy 1877), and by the time the first settlers arrived in 1609, pigs had already decimated seabird populations on the main islands (Strachy 1625). Petrel populations that survived on satellite islets where there were no pigs were heavily harvested for food, with adults, nestlings and eggs taken (Butler 1619). The colonists also brought with them other exotic species, including rats, cats and dogs (Lefroy 1877). These new predators, together with extensive burning and deforestation during the first two decades of settlement, further reduced the remnant populations of Bermuda Petrel (Verrill 1902). By 1621 the Bermuda Petrel could no longer be located (Smith 1627) and for the next three centuries it was thought to be extinct (Verrill 1902, Murphy and Mowbray 1951).
The first modern record of the species dates from February 1906 when a live specimen was collected on Gurnet Rock, Bermuda (Bradlee 1906). Initially, this specimen was erroneously identified as a Mottled Petrel Pterodroma inexpectata (Bradlee 1906). It was not until 1916 that the specimen was compared with subfossil...