Bermuda Petrel Pterodroma cahow

  • Order: Procellariiformes
  • Family: Procellariidae
  • Monotypic
  • Authors: Edward S. Brinkley and Kate Sutherland
Sections

Distribution

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  • Year-round
  • Migration
  • Breeding
  • Non-Breeding
Distribution of the Bermuda Petrel
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eBird range map for Bermuda Petrel

Generated from eBird observations (Year-Round, 1900-present)

Distribution in the Americas

Bermuda Petrel currently is known to nest only on six small islands off the southeastern part of Bermuda, around Castle Harbour (Castle Roads): Horn Rock, Long Rock, Inner Pear Rock, Green Island, and more recently Nonsuch Island (where translocated chicks have begun breeding) and Southampton Island (spontaneously colonized by three pairs in the 2012-2013 breeding season). A former nesting island, Outer Pear Rock, is no longer used, and the type locality, Gurnet Rock, is difficult of access and does not provide adequate habitat for nesting. The last nesting petrels on Outer Pear Rock were killed by a Brown Rat (Rattus norvegicus) in the nesting season of 1977-1978. The Castle Harbour islands are protected as a Nature Reserve and National Park.

Bermuda Petrel has been observed at sea in the vicinity of these islands regularly since 1993—typically in late autumn, when birds are preparing to return to nest sites and/or courting in the late afternoon and early evening—but there are very few observations of the species from pelagic waters around Bermuda. Up to 20 were noted 3-4 June 1997 some 475 km east-northeast of Bermuda (Wingate et al. 1998); data gathered from Lotek data-loggers attached to the legs of several Bermuda Petrels 2009-2011 indicate that this area often is frequented by Bermuda Petrels.

Although the nesting islands are off limits to visitors at all times, many observers have been able to study Bermuda Petrels using a spotting scope at Cooper's Point (accessed only with permission), usually during the late afternoon from mid-October through late November.

There is limited published information on the at-sea range of Bermuda Petrel; much of what is known is based on sightings at sea, many of which have been documented by photograph since the late 1990s. Several reports of the species at sea between 1979 and 1991 appear to refer to Black-capped Petrel (Pterodroma hasitata), an understandable error, inasmuch as Black-capped was very little known until the late 1970s, and field identification of Bermuda Petrel was not elucidated until 1994 (Wingate et al. 1998). Other older reports of Bermuda Petrel may pertain instead to one or more members of the complex of gadfly petrels that nest in the Macaronesian islands, from the Cape Verde Islands north to the Desertas; the taxonomic status of these petrels remains unsettled (Jesus et al. 2009), but they appear to be close relatives of Bermuda Petrel (see Related Species) and are similar in size (though most show a more extensively slaty underwing than Bermuda Petrel; see Distinguishing Characteristics and Similar Species). Since 1991, petrels of this group have been recorded annually and photographed on numerous occasions off North Carolina. Most literature refers to these records as pertaining to Fea's Petrel (Pterodroma feae); up to 10 have been recorded per year there, plus three records from Virginia, one off Long Island, New York, four off Georgia, one off Nova Scotia, and one off Newfoundland.

Between 1983 and 2016, Bermuda Petrel was reported or recorded on 31 occasions in the Gulf Stream (or in waters influenced by the Gulf Stream) off North Carolina, with a single-day high count of 3 birds on 29 May 2009, 2 birds on both 27 May 2002 and 23 May 2005, but all other records pertaining to single individuals. The dates of sight records range from 18 April (D. S. Lee; Lee 1984) through possibly 20 December on the Continental Shelf Christmas Bird Count (American Birds 39: 554; D. S. Lee, W. Irvin; Lee 1987, described as "probable"). Confirmed photographic records range from 26 May through 22 September (J. B. P. Patteson, K. Sutherland). A Bermuda Petrel was seen but not photographed off the South Carolina coast 30 May 2009 (N. Dias, personal communication). There is also a credible sight record of the species from 32° 40’ N, 75° 43’ W, far east of the South Carolina coast, though closer to Carteret County, North Carolina, on 31 July 1993 (T. Hass, J. Poston; Wingate et al. 1998). More recently, there are photographic records of a juvenile Bermuda Petrel from deep waters off Massachusetts 28 June 2010 (P. Duley; Duley 2010) and a Bermuda Petrel of unknown age (but in fresh, unworn plumage) off Virginia Beach, Virginia 12 August 2013 (T. Johnson, in litt.). A freshly plumaged Bermuda Petrel was photographed 21 April 2014 in Canadian waters over Georges Canyon about 242.6 km (131 nautical miles) south of Cape Sable, Nova Scotia (Michael P. Force), in an area with high numbers of marine mammals including Long-finned Pilot Whales (Globicephala melas), Sei Whales (Balaenoptera borealis), Humpback Whales (Megaptera novaeangliae), and Bottlenose Dolphins (Tursiops truncatus).

Of the 31 North Carolina records, 28 have been made by Captain J. B. P. Patteson of Frisco, North Carolina, whose pelagic birding and natural history tours operate year-round out of Hatteras as well as occasionally from ports farther north. Captain Patteson first documented Bermuda Petrel off Hatteras Island, North Carolina at 35° 37’ N, 74° 43’ W on 31 July 1993 (Wingate et al. 1998), over waters ca 1400-1600 m deep. He detected and documented the species annually from 1995 through 2009, with as many as 5 individuals per year. Despite extensive exploration of pelagic waters off North Carolina's Outer Banks in 2010, 2011, 2012, and 2016, no Bermuda Petrels were recorded in those years, but single birds were noted off Hatteras on 3 June 2013, 30 August 2014, and 21 May 2015. A Bermuda Petrel was observed 6 June 2009 from a large cruise ship whose location at the time of the observation was described as "approximately 160 nautical miles east-northeast of Cape Hatteras" (G. Mackiernan, B. Cooper, in litt.).

From 2009 through 2012, 12 Bermuda Petrels were fitted with Lotek data-loggers, which have provided evidence that the petrels range much farther from Bermuda than previously suspected, even into the cold waters off northeastern Canada, which may provide a rich supply of food for petrels when feeding young. As yet, there is no report or record of the species from Canadian waters, but observers in these areas should be mindful of its occurrence there. Preliminary results provided by the data-loggers indicate that about one-third of tagged Bermuda Petrels spent their time to the north and west of Bermuda, normally not more than 1440 km from the nesting grounds. Adults cover 5000 km or more during a foraging trip, following different courses from Bermuda but often foraging over Gulf Stream edges. Data-loggers indicate that the species ranges northwest to the Bay of Fundy, into the Gulf of St. Lawrence and over the Grand Banks, and one individual ranged to about 200 km off southwestern Ireland (Madeiros 2009, 2013; Madeiros et al. 2014).

Distribution outside the Americas

A Bermuda Petrel, apparently an adult male, was first discovered prospecting nest sites at Ilhéu da Vila, an islet off Santa Maria in the Azores, on 17 and 21 November 2002 and was banded (Bried 2003, Bried and Magalhães 2004); the same bird was noted at this site again on 19 and 21 November 2003 and 12 and 13 December 2006 (Gantlett 2004, 2007; J. Bried, in litt.). There is no other record of the species on land away from Bermuda. Data from Lotek data-loggers attached to Bermuda Petrels since 2009 indicate that the species ranges into the northeastern North Atlantic at least as far as waters off Ireland, and that in the nonbreeding season, about half of the tagged petrels remained in the vicinity of the Azores (Madeiros 2010, Madeiros et al. 2014). These devices are relatively accurate, perhaps within 200 km (Phillips et al. 2004). There are no at-sea records of the species in the vicinity, but observers in Ireland, the United Kingdom, western Europe, and Macaronesia should be be watchful for Bermuda Petrels in their regions.

Habitat

For breeding, Bermuda Petrels utilize small offshore islets exclusively, making their nests in burrows, usually at the end of tunnels. In places where there is topsoil, the birds may excavate these burrows themselves, but most birds now nest in artificial burrows designed to maximize breeding success. All of the breeding islets are composed of aeolian limestone, whose uneven stratification makes it susceptible to fragmentation by heavy seas. Formerly, Bermuda Petrels utilized a wider variety of terrestrial habitats for nesting, and although there are no written accounts detailing precisely the types of habitats occupied, it is clear that the birds excavated burrows in areas with extensive topsoil and trees, as do some of their congeners.

When not at the nest site, Bermuda Petrels inhabit pelagic environments, apparently foraging primarily over deep (> 200 m) water of the continental slope and seaward; there are no reports or records of the species from inshore (littoral waters) and no reports of storm-wrecked birds in terrestrial environments (by contrast, there are nearly 100 such records for Black-capped Petrel Pterodroma hasitata). Several pelagic records of Bermuda Petrel (e.g., Duley 2010) are from areas of ocean characterized by temperature breaks or thermoclines over the continental slope, where upwelling of nutrients and higher concentrations of favored prey items would occur. Few data are available at present to adduce characteristics of pelagic waters in which this species most regularly forages, but use of Lotek data-loggers on several individuals per year since 2009 has shown that Bermuda Petrels forage not just in waters adjacent Bermuda or the Carolinas but regularly into the cold waters off New England and Newfoundland, and that many also spend the nonbreeding season in the vicinity of the Azores (Madeira 2010).

Historical changes

Bermuda Petrel's population was reduced, chiefly by human exploitation (hunting) and by introduced mammalian predators, from perhaps a million or more (Wilkinson 1950) to a low of about seven pairs in 1951 (Murphy and Mowbray 1951), with 105 breeding pairs in 2012/2013 (at least 50 fledged successfully), which suggests a total population of perhaps 350 individuals (Madeiros 2010).

Fossil history

Shufeldt (1916, 1922) analyzed fossil and subfossil bones from Bermudian caves and noted an abundance of remains of a gadfly petrel species, which he named Æstrelata gularis in the same year that Nichols and Mowbray (1916) described Æstrelata cahow. The latter name applies to Bermuda Petrel, as it was published first and was based on a specimen.

Recommended Citation

Brinkley, E. S. and K. Sutherland (2017). Bermuda Petrel (Pterodroma cahow), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.berpet.01