Bermuda Petrel

Pterodroma cahow

(c) Jeremy Madieros
  • Shearwaters, Fulmars, Petrels
  • Procellariiformes
  • Petrel cahow
  • Pétrel des Bermudes

The once-common Bermuda Petrel has the dubious distinction of being one of the world's rarest seabirds. This nocturnal ground-nesting petrel, now being laboriously brought back from the brink of extinction, is a symbol of hope for nature conservation. Commonly known in Bermuda as the Cahow, a name derived from its eerie cries, this endemic species is the national bird of Bermuda, and was featured on the original Bermudian one and ten dollar bills.

Appearance Description
Bermuda Petrels average 15 inches in length, with a wingspan of 35 inches. Their brownish-gray upper body includes a cap that covers the eye and a partial brown collar on the nape. The bill is black, and the white under-wings are edged in black; the under parts are otherwise entirely white. A narrow whitish band is visible at the base of the tail. The long-wings on this medium-sized seabird make it an excellent flier. The very similar Black-capped Petrel, a larger and darker bird with a more extensive white rump, occurs regularly off the North Carolina coast.
Range Distribution
Bermuda Petrels breed only on suboptimal rocky islets in Castle Harbor, within the oceanic Bermuda island group, located in the western reaches of the Sargasso Sea. During the non-breeding season, the birds range widely in the North Atlantic, to the western edge of the Gulf Stream, where they feed on squid and fish.
Bermuda Petrels formerly excavated inland nesting burrows, in sand or soft soils, but introduced predators preclude them from occupying this habitat. The birds now nest only on small, rocky offshore islets in Castle Harbor, Bermuda, in suboptimal eroded limestone crevices or artificial burrows. They spend their adult life at sea.
While small squid make up the bulk of the Cahow's diet, the birds also feed on shrimp and various small fish.
Five year old Cahows return to their former nesting grounds to begin breeding. Breeding takes place from January to June. Cahows typically mate for life. The birds' nocturnal aerial courtship is now disrupted by lights from human facilities. These slow breeders lay only one egg. The single white egg is incubated for 51 to 54 days, with parents visiting the nesting burrows only at night. The chick is brooded for only a day or two, and fledges after 90 to 100 days. The breeding grounds are abandoned by the petrels from mid-June to mid-October.
In the non-breeding season, birds likely move north into the Atlantic, following the warm waters on the western edges of the Gulf Stream. There are confirmed records off the coast of North Carolina.
  • 180
  • 150
  • Endangered
  • Globally endangered
Population Status Trends
Bermuda Petrels once bred abundantly throughout Bermuda. After 1621, the bird was considered extinct for about three centuries, until their continued existence was confirmed in the early 1900s. In 1951, 18 pairs were rediscovered breeding on Castle Harbor. Forty-five years of intensive management has resulted in slow but steady increases in population of this species, but total numbers remain extremely small. Breeding success has increased from 5 percent per year in the 1950s to more than 25 percent per year in the 1990s, with 70 pairs fledging a record 40 young in 2003, and 71 pairs fledging 35 young in 2005. BBS and CBC data are not available for this species. The Bermuda Petrel is federally listed as an Endangered Species.
Conservation Issues
The Cahows' eerie nocturnal cries deterred superstitious early Spanish explorers from settling on Bermuda. But the bird was nearly exterminated in the 1600s by British colonists who hunted it for food, destroyed its breeding habitat, and introduced predators, including rats, dogs, and cats. Bermuda Petrels were considered extinct for about 300 years.
Following the birds' rediscovery in 1951, the Bermuda Conservation Programme periodically removed rats, installed concrete nesting burrows with wooden baffles over burrow entrances to keep out larger, competing White-tailed Tropicbirds, and ecologically restored a larger nearby island—Nonsuch Island—as a potential nesting site. The Castle Harbor islands were made a national park.
Under legal protection and intensive management, the species is slowly recovering. However, nearby light pollution hampers the birds' nocturnal courtship. In addition, contaminants may contribute to increased egg failure. But the primary threat is limited breeding habitat. Increasing sea levels and storm activity flooded nesting sites in the 1990s, and Hurricane Fabian washed over the breeding islets in 2003, destroying many nesting burrows.
In 2004, with a new artificial burrow complex built on a higher section of one islet, a sound attraction system pioneered by Audubon's Seabird Restoration Program was set up, and adult Cahows moved there from the destroyed sites. Three pairs occupied burrows in the new site by the spring of 2005. Beginning in 2004, a few Bermuda Petrel chicks were translocated to Nonsuch Island, fed, and monitored, in the hopes that they would imprint on these surroundings and return when mature to nest. All translocated chicks fledged successfully. This project is scheduled to continue for three more years, with plans to translocate a total of about 100 chicks.
What You Can Do
Join beach cleanups in your area. Properly discarding of debris, particularly plastic, will prevent Bermuda Petrels and other seabirds from eating it.
Don't discard used oil into city sewers or municipal water supplies. It can end up in the ocean where petrels rest and feed; if their feathers become oiled, the birds are no longer waterproof and cannot survive.
Never let balloons drift off; petrels can become entangled in the strings, and marine mammals can mistake the balloons for food.
Cut up monofilament fishing line, which can entangle coastal birds, prior to discarding it.
Join the Bermuda Audubon Society. To learn more, visit:
Find out about actions you can take including Audubon programs and activities.
More Information
Learn more about this species and other birds through these resources.
Natural History References
Kaufman, Kenn. Lives of North American Birds. Houghton Mifflin Company, New York, 1996
Sibley, David Allen. The Sibley Guide to Birds. Alfred A. Knopf, Inc., New York, 2000
BirdLife International 2006. Species factsheet: Pterodroma cahow. In: IUCN 2006. 2006 IUCN Red List of Threatened Species.
Conservation Status References
Kaufman, Kenn. Lives of North American Birds. Houghton Mifflin Company, New York, 1996
Sibley, David Allen. The Sibley Guide to Birds. Alfred A. Knopf, Inc., New York, 2000
BirdLife International 2006. Species factsheet: Pterodroma cahow. In: IUCN 2006. 2006 IUCN Red List of Threatened Species.