Bermuda Petrel Pterodroma cahow
Version: 2.0 — Published November 16, 2020
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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 (6); 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, 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 (6). 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 (2), 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 Identification 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; 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 April 1983 and June 2020, Bermuda Petrel has been reported or recorded on 36 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 well-documented 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; 6). More recently, there are photographic records of a juvenile Bermuda Petrel from deep waters off Massachusetts 28 June 2010 (P. Duley; Duley 2010) and 21 Sep 2019 (T. Johnson, in litt.). A Bermuda Petrel of unknown age (but in fresh, unworn plumage) was photographed off Virginia Beach, Virginia 12 August 2013 (T. Johnson, in litt.). A freshly plumaged Bermuda Petrel was photographed 21 April 2014 near 41.25, -66.283, in Canadian waters over Georges Canyon about 242.6 km (131 nautical miles) south of Cape Sable, Nova Scotia (Michael P. Force, Nicholas Metheny), 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 36 North Carolina records, 33 have been made by Captain J. B. P. Patteson of Frisco, North Carolina and Captain K. Sutherland of Hatteras, 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 (6), over waters ca 1,400-1,600 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, 2016, 2017, and 2018, no Bermuda Petrels were recorded in those years, but single birds were noted off Hatteras on 3 June 2013, 30 August 2014, and 25 May 2015, and in 2019, single birds were documented 8 May, 9 May, and 29 May (all adults), and 27 July (juvenile). 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.). For at-sea records of the species after June 2020, consult data in ebird.org.
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. 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 1,440 km from the nesting grounds. Adults cover 5,000 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 (14, 15, 16). Results of surveys with more sophisticated GPS tags (begun in the 2019-2020 nesting season) should be published in the near future.
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 (17, 18); the same bird was noted at this site again on 19 and 21 November 2003 and 12 and 13 December 2006 (19, 20; 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 (21, 16). These devices are relatively accurate, perhaps within 200 km (22). Away from the Azores, the only direct observation of the species in the eastern North Atlantic was made 19 May 2014, a single bird 170 nautical miles west-northwest of Slea Head, County Kerry, Ireland, in the continental slope waters of Porcupine Bank (water depth 1030 m). The bird was studied and photographed from the R/V Celtic Voyager by Niall T. Keogh, Ryan Wilson-Parr, Simon Berrow, and Rossa Meade during a survey of cetaceans and seabirds. Based on data from tagging projects, observers in Atlantic Canada, the United Kingdom, western Europe, and Macaronesia should be be watchful for Bermuda Petrels in their regions as well.
Historical Changes to the Distribution
Bermuda Petrel's population was reduced, chiefly by human exploitation (hunting) and by introduced mammalian predators, from perhaps a million or more (23) to a low of about seven pairs in 1951 (5). With 134 breeding pairs in 2020, the population is likely nearing 500 individuals or possibly more.