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Bermuda Petrel Pterodroma cahow
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Successful conservation has increased the population of this species, but it remains extremely small and the species consequently qualifies as Endangered. If the population continues to grow, which recent figures suggest it has, the species will warrant downlisting to Vulnerable in due course.

Taxonomic source(s)
AERC TAC. 2003. AERC TAC Checklist of bird taxa occurring in Western Palearctic region, 15th Draft. Available at: # _the_WP15.xls#.
Brooke, M. de L. 2004. Albatrosses and Petrels Across the World. Oxford University Press, Oxford.
del Hoyo, J.; Collar, N. J.; Christie, D. A.; Elliott, A.; Fishpool, L. D. C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

38 cm. Medium-sized, long-winged, brownish-grey and white gadfly petrel. Brownish-black cap extending to eye, but interrupted by pale eyebrow. Brownish nape extending towards upper breast to form partial collar. Brownish-grey mantle, upperwing and tail. Pale uppertail-coverts may form narrow whitish band. Entirely white underparts. White underwing with narrow black trailing edge, black tip, extending narrowly onto leading edge. Black bill. Pink legs, pink feet proximally, black distally. Similar spp. Black-capped Petrel P. hasitata is larger with white hindneck and more extensive white rump, but sometimes separation at sea may be impossible. Great Shearwater Puffinus gravis is larger, darker and less contrasting above, lacks black edge to underwing and has slower wing-beats and less erratic flight.

Distribution and population
Pterodroma cahow once bred abundantly throughout Bermuda (to UK). It was thought extinct for almost three centuries, until reported (with specimens) during the first half of the 20th century. In 1951, 18 pairs were rediscovered breeding on suboptimal rocky islets (total area 1 ha) in Castle Harbour. Intensive management has resulted in slow but steady increases, and the population was estimated at 250 birds in 2005 (J. Madeiros in litt. 2005), with 70 pairs fledging a record 40 young in 2003 (Madeiros 2003), and 71 pairs fledging 35 young in 2005 (J. Madeiros in litt. 2005). More recently, 40 young fledged in 2008 from 85 established active nest sites and at least 35 chicks hatched in 2009 (Madeiros unpublished data). By 2011, the population reached 98 nesting pairs (Madeiros 2011). From 40 chicks on all islands in 2008, 21 chicks were translocated in May to Nonsuch, forming the last year of the translocation project (Madeiros 2008). Fourteen individuals fledging from Nonsuch Island after translocation in 2005 and 2006 were observed in 2009 returning to the island and entering artificial burrows. One chick was born on the island in 2009 (Madeiros unpublished data). By 2011, 22 translocated birds have returned to Nonsuch, and 8 more translocated birds returned to the original nesting islets. Non-translocated birds have also been recorded on Nonsuch indicating a sufficient nucleus of translocated birds to attract non-translocated individuals into the colony (Madeiros 2011). In the non-breeding season, birds probably move north into the Atlantic, following the warm waters on the western edges of the Gulf Stream (Wingate 1997). There are confirmed records off the coast of North Carolina, USA (D. S. Lee in litt. 1998, Wingate et al. 1998), and one bird was captured in the Azores in November 2002 and recaptured in November 2003 and December 2006 (Bried 2003, J. Bried in litt. 2010).

Population justification
The population is estimated to number 250 individuals, including 71 breeding pairs and thus a minimum 142 mature individuals (J. Madeiros in litt. 2005).

Trend justification
The population has increased from 18 pairs in 1951 to 71 pairs in 2005. This is equivalent to an increase of well over 79% in three generations, given the species's long lifespan. Records of 40 chicks fledged in 2008 and 35 chicks hatched in 2009 suggest the population continues to increase.

It formerly nested in soil burrows, but such habitat is not available on current breeding islands and it now nests in suboptimal, natural erosion limestone crevices and artificial burrows. The breeding season is January-June, and breeding success has increased from less than 5% per year in the 1950s to more than 25% per year in the 1990s (Wingate 1997). Ringing recoveries have shown that birds first return to breed four years after fledging (Madeiros in litt. 2006). The breeding grounds are not visited by birds between mid-June and mid-October (Wingate 1997), with adults returning from mid-October (Madeiros 2008). Results from geolocational tags showed that individuals can cover in excess of 5,000 km during a foraging trip, following different courses from Bermuda but generally all foraging over the Gulf Stream (Madeiros unpublished data). During the non-breeding season they have been recorded in the Gulf Stream, north to the Bay of Fundy, into the Gulf of St. Lawrence and over the Grand Banks, with one individual recorded 125-150 miles off southwest Ireland (Madeiros 2009).

The drastic population decline is attributed to habitat loss, exploitation and predation. Its recovery has been hampered by competition from White-tailed Tropicbird Phaethon lepturus for nest-sites and subadult predation from a single snowy owl (the first ever recorded in Bermuda) on Nonsuch Island, which was eradicated, having eaten 5% of the population (Dickinson 2007). Light pollution from a nearby airport and NASA tracking station adversely affects nocturnal aerial courtship (Wingate et al. 1998). The threat of sea-level rise and increased storm activity appears real, with five or more major floods affecting burrows in the 1990s, after 25 years without significant problems (Wingate et al. 1998). Category three hurricane Fabian in 2003 overwashed three of the four breeding islets, damaging or destroying a significant number of nest burrows (J. Madeiros in litt. 2005). Increasing egg failure may be attributable to contaminants (Wingate 1997). Rats also swam to one breeding island in April 2005, but were successfully eradicated within two weeks without loss to the Cahows (J. Madeiros in litt. 2005). Unfortunately this pattern appeared to be repeated in March 2008, with four chicks killed on one of the nesting islets. Immediate baiting produced a dead black rat Rattus rattus. However, as the islands were all baited at the beginning of the nesting season, this incident pointed out the need for constant vigilance of reintroduction and a requirement to provide fresh bait on the islands throughout the nesting season (Madeiros 2008).

Conservation Actions Underway
CMS Appendix I. Since 1961, there has been management of nesting-grounds, including the creation of artificial burrows, periodic removal of rats and the elimination of nest-site competition from P. lepturus (by installing baffles over burrow entrances). As part of the Bermuda Conservation Programme, potential breeding islands (e.g. Nonsuch) have been reforested with native flora in an attempt to attract nesting petrels (Wingate et al. 1998). The Castle Harbour islands are a National Park and Nature Reserve (J. Madeiros in litt. 2005). In 2004 and 2005 efforts were made to attract adult Cahows, displaced from low-lying nest burrows destroyed by hurricane Fabian, on the main breeding islet to a new artificial burrow complex built on a more elevated section of the islet. Using a combination of a sound attraction system set up among the new nests and physical translocation of adult Cahows from the destroyed sites, three pairs occupied burrows in the new complex by March 2005 (J. Madeiros in litt. 2005). A project is now underway to establish a new nesting colony on the Nonsuch Island Living Museum, which is much larger and contains more suitable breeding habitat than the present suboptimal breeding islets. The project involves physical translocation of chicks from the present breeding islets to a new complex of artificial burrows on Nonsuch, so that they will imprint on the new site and return when mature to establish their nests at the new location. In 2004, the trial year of the project took place with 14 chicks moved to Nonsuch, where they were fed and monitored every other day until departure, with all fledging successfully. In 2005, 21 chicks were translocated, with all again fledging successfully by mid-June. This project was scheduled to continue for three more years, with a target of 90 to 100 chicks in total being translocated over a five-year period (J. Madeiros in litt. 2005). In 2009, the first adult-fed Cahow for 400 years hatched on Nonsuch Island (Dobson 2009). So far, 79 relocated chicks have fledged on Nonsuch, with only one fatality (Dickinson 2007). A Sound Attraction System was also set up in 2007 to help encourage birds to stay and prospect on Nonsuch, and overcome any tendency for young birds to be attracted back to the activity at the original nesting islets (Madeiros 2008). A total of 171 fledglings were ringed between 2002-2007, with 31 confirmed having returned (including 4 repatured on Nonsuch Island), representing cohorts from four nesting seasons, 2002 to 2005 (Madeiros 2008).Conservation Actions Proposed
Maintain all management activities at current nesting-grounds. Investigate whether contaminants are increasing egg failure (Wingate 1997). Continue to manage the new breeding colony on Nonsuch Island (Wingate 1997, Madeiros 2003, J. Madeiros in litt. 2005). Investigate the pelagic and foraging range of the species using new data logger technology (J. Madeiros in litt. 2005).

Related state of the world's birds case studies

Bried, J. 2003. A Bermuda Petrel on the Azores - a new Western Palearctic bird. Birding World 16: 22.

Collar, N. J.; Gonzaga, L. P.; Krabbe, N.; Madroño Nieto, A.; Naranjo, L. G.; Parker, T. A.; Wege, D. C. 1992. Threatened birds of the Americas: the ICBP/IUCN Red Data Book. International Council for Bird Preservation, Cambridge, U.K.

Dickinson, R. 2007. Seeking higher ground. Audubon 109(5): 54-63.

Dobson, A. 2009. First Cahow hatches on Nonsuch Island for nearly 400 years. Bermuda Audubon Society Newsletter 20(1): 1-2.

Madeiros, J. 2003. Report on the 2003 Cahow nesting season - another record year! Bermuda Audubon Society Newsletter 14: 8-9.

Madeiros, J. 2008. Cahow nesting season update April 2008. Bermuda Audubon Society Newsletter 19(1): 2-5.

Madeiros, J. 2009. Cahow update. Bermuda Audubon Society Newsletter 20(2): 2-3.

Madeiros, J. 2011. Cahow Report. Bermuda Audubon Society Newsletter 22(1): 5-6.

Wingate, D. 1997. The Cahow species account. In: Lee, D.S.; Schreiber, E.A.; Walsh-McGehee, M. (ed.), CBIRDS: the workshop. Draft species account, Society for Caribbean Ornithology, Aruba.

Wingate, D. B.; Hass, T.; Brinkley, E. S.; Patterson, J. B. 1998. Identification of Bermuda Petrel. Birding 30: 19-36.

Further web sources of information
Alliance for Zero Extinction (AZE) species/site profile. This species has been identified as an AZE trigger due to its IUCN Red List status and limited range.

Audubon WatchList

Click here for more information about the Alliance for Zero Extinction (AZE)

Detailed species account from the Threatened birds of the Americas: the BirdLife International Red Data Book (BirdLife International 1992). Please note taxonomic treatment and IUCN Red List category may have changed since publication.

Detailed species account from the Threatened birds of the Americas: the BirdLife International Red Data Book (BirdLife International 1992). Please note, taxonomic treatment and IUCN Red List category may have changed since publication.

Explore HBW Alive for further information on this species

Recuento detallado de la especie tomado del libro Aves Amenazadas de las Americas, Libro Rojo de BirdLife International (BirdLife International 1992). Nota: la taxonomoía y la categoría de la Lista Roja de la UICN pudo haber cambiado desde esta publicación.

Search for photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Anderson, O., Calvert, R., Clay, R., Isherwood, I., Mahood, S., Temple, H., Wege, D.

Lee, D., Madeiros, J.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2016) Species factsheet: Pterodroma cahow. Downloaded from on 28/10/2016. Recommended citation for factsheets for more than one species: BirdLife International (2016) IUCN Red List for birds. Downloaded from on 28/10/2016.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

To contribute to discussions on the evaluation of the IUCN Red List status of Globally Threatened Birds, please visit BirdLife's Globally Threatened Bird Forums.

Additional resources for this species

ARKive species - Cahow (Pterodroma cahow) 0

Key facts
Current IUCN Red List category Endangered
Family Procellariidae (Petrels, Shearwaters)
Species name author (Nichols & Mowbray, 1916)
Population size 142 mature individuals
Population trend Increasing
Distribution size (breeding/resident) 623,000 km2
Country endemic? Yes
Links to further information
- Additional Information on this species