Justification 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, the species will warrant downlisting to Vulnerable in due course.

Family/Sub-family Procellariidae

Species name author (Nichols & Mowbray, 1916)

Taxonomic source(s) AERC TAC (2003), AOU checklist (1998 + supplements), Brooke (2004), Sibley and Monroe (1990, 1993)

Identification 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.

Population estimate

Population trend

Range estimate (breeding/resident)

Country endemic?

140

increasing

636,000 km²

Yes

Range & 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 2005⁷, with 70 pairs fledging a record 40 young in 2003⁵, and 71 pairs fledging 35 young in 2005⁷. In the non-breeding season, birds probably move north into the Atlantic, following the warm waters on the western edges of the Gulf Stream². There are confirmed records off the coast of North Carolina, USA^1,3, and one bird was captured in the Azores in November 2002⁶.

Important Bird Areas Click here to view map showing IBAs where species is recorded and triggers any of the IBA criteria.

Ecology: 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 1990s². Ringing recoveries have shown that birds return to birds first return to breed four years after fledging⁸. The breeding grounds are not visited by birds between mid-June and mid-October².

Threats 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. Light pollution from a nearby airport and NASA tracking station adversely affects nocturnal aerial courtship³. 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 problems³. Category three hurricane Fabian in 2003 overwashed three of the four breeding islets, damaging or destroying a significant number of nest burrows⁷. Increasing egg failure may be attributable to contaminants². Rats also swam to one breeding island in April 2005, but were successfully eradicated within two weeks without loss to the Cahows⁷.

Conservation measures 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 petrels³. The Castle Harbour islands are a National Park and Nature Reserve⁷. 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 physicall translocation of adult Cahows from the destroyed sites, three pairs occupied burrows in the new complex by March, 2005⁷. 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 is scheduled to continue for three more years, with a target of 90 to 100 chicks in total being translocated over a five-year period⁷.

Conservation measures proposed Maintain all management activities at current nesting-grounds. Investigate whether contaminants are increasing egg failure². Continue to manage the new breeding colony on Nonsuch Island^2,5,7. Investigate the pelagic and foraging range of the species using new data logger technology⁷.

References Collar et al. (1992). 1. D. S. Lee in litt. (1998), 2. Wingate (1997), 3. Wingate et al. (1998). 4. J. Madeiros in litt. (2002). 5. Madeiros (2003). 6. Bried (2003). 7. J. Madeiros in litt. (2005). 8. Madeiros in litt. (2006).

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

Fully 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.

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.

Text account compilers Rob P Clay (Guyra Paraguay), Isabel Isherwood (BirdLife International), Simon Mahood (BirdLife International), Helen Temple (BirdLife International), David Wege (BirdLife International)

IUCN Red List evaluators Stuart Butchart (BirdLife International), Simon Mahood (BirdLife International)

Recommended citation BirdLife International (2009) Species factsheet: Pterodroma cahow. Downloaded from http://www.birdlife.org on 10/2/2010

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.

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