Bermuda petrel

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Bermuda petrel
Pterodroma cahow.jpg
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Procellariiformes
Family: Procellariidae
Genus: Pterodroma
Species: P. cahow
Binomial name
Pterodroma cahow
(Nichols & Mowbray, 1916)

The Bermuda petrel (Pterodroma cahow) is a gadfly petrel. Commonly known in Bermuda as the cahow, a name derived from its eerie cries, this nocturnal ground-nesting seabird is the national bird of Bermuda and can be found on Bermudan money. It is the second rarest seabird on the planet and a symbol of hope for nature conservation. They are known for their medium-sized body and long wings. The Bermuda petrel has a greyish-black crown and collar, dark grey upper-wings and tail, white upper-tail coverts and white under-wings edged with black, and the underparts are completely white.

For 330 years, it was thought to be extinct. The dramatic rediscovery in 1951 of eighteen nesting pairs made this a "Lazarus species", that is, a species found to be alive after having been considered extinct. This has inspired a book and two documentary films. A national programme to preserve the bird and restore the species has helped increase its numbers, but scientists are still working to enlarge its nesting habitat on the restored Nonsuch Island.


Initially they were superabundant throughout the archipelago, but because of habitat degradation and invasion of mammals, the bird's suitable nesting areas have dwindled to four islets in Castle Harbor, Bermuda, in the warm waters of the Gulf Stream, some 650 miles east of North Carolina. The cahow is a slow breeder, but excellent flier. It visits land only to nest and spends most its adult life on the open seas ranging from the North Atlantic coastal United States and Canada to waters off western Europe.[2] After 3–4 years at sea, males return to breeding islands to create nests. Breeding season takes place during January and June. They nest in underground burrows and only the ones that can be in complete darkness are chosen. Females return after 4–6 years at open sea looking for a mate; the females lay one egg per season. 40% to 50% fail to hatch. Eggs are incubated by both parents and take 53–55 days to hatch. Hatching occurs during between May and June. Cahows mate for life and typically return to the same nest each year.


The Spanish sailors of the 1500s used Bermuda and its surrounding islands as a waypoint for their raids against the Incas and other civilizations. At that time, cahows were abundant and formed dense, noisy colonies. These sailors, as Diego Ramirez writes in 1603, would take up to 400 birds a night for food. In addition to eating birds, conquistadors brought hogs to the island to sustain themselves over their voyage. These hogs interfered with the ground-nesting cahow and disrupted their breeding cycle. Along with these new species brought by settlers, the remaining Bermuda petrel population also decreased due to widespread burning and deforestation by the settlers during the first 20 years of settlement.

Following the Spanish arrival in Bermuda, the English ship the Sea Venture wrecked on the island in 1609. Those men that were shipwrecked culled the fattest individual petrels and harvested their eggs in abundance, especially in January when other food sources were diminished.

Bermuda's colonization by the English introduced species like rats, cats and dogs, and mass killings of the birds by these early colonists decimated the numbers of birds. Despite being protected by one of the world's earliest conservation decrees, the governor's proclamation "against the spoyle and havocke of the Cohowes", the birds were thought to have become extinct by the 1620s.

In 1935, William Beebe of the New York Zoological Society had hopes of rediscovering the bird. By June he was presented with an unidentified seabird that had struck the St. Davids Light house in Bermuda. The bird was then sent to American ornithologist Robert Cushman Murphy of The American Museum of Natural history in New York. He identified the bird as a Bermuda petrel. Six years later, Bermudian naturalist Louis L. Mowbray received a live Bermuda petrel that had collided with a radio antenna tower. The bird was released after rehabilitation two days later.[3]

In 1951, 18 surviving nesting pairs were found on rocky islets in Castle Harbour by Murphy and Mowbray and with them was a 15-year-old Bermudian boy, David B. Wingate, who would become the primary conservationist in the fight to save the bird.


David B. Wingate devoted his life after that to saving the bird. After university studies and other work, in 1966 Wingate became Bermuda's first conservation officer.

Nonsuch Island was a near desert after centuries of abuse, neglect and habitat destruction. The measures that had to be taken weren't just for conserving what was left but also to re-create what had been lost. After studying the birds and their habits, Wingate designed and donated artificial nest boxes to the Cahow Recovery Project funded by the Bermuda Audubon Society. These nests were an effort made toward the restoration of the Bermuda Petrel. 50 artificial burrows, stabilized with concrete, had been built for the birds on Nonsuch Island. Because Bermuda Petrels have the natural instinct to dig their own burrows, the design of these burrows meet the birds nesting needs. Wingate’s goal is to restore the habitat on Nonsuch Island as a viable base for the species. It is hoped that the artificial burrows will assist in the recovery of the Cahow for its future survival.[4] 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[5]

All but three translocated birds fledged successfully, with the first returning to Nonsuch Island in February 2008. The first Bermuda Petrel egg on Nonsuch Island in more than 300 years was laid in January 2009, and the resultant fledgling departed in June of the same year.[6]

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. 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[7]

Thanks to the conservation efforts over the past two decades and extensive legal protection, the main threat for the future of the bird is still the lack of a suitable breeding habitat. 80% of the Bermuda Petrel nest in artificial burrows. Hurricane Fabian destroyed about 15 nesting burrows in 2003, the rising ocean levels have caused erosion on the petrel's preferred breeding grounds on the islets. Researchers hope the repopulation of the Nonsuch Island with chicks will result in their translocation timed so they will imprint on these surroundings and return here for nesting.[8] This work is being undertaken by Bermuda Conservation Officer Jeremy Madeiros assisted by the Australian petrel specialist Nick Carlile. The global population of this bird in 2005 was about 250 individuals. A cahow was seen off the west coast of Ireland in May 2014, the furthest the species has ever been seen from Bermuda.


Cahows typically eat small fish, squid and shrimp-like crustaceans. They also predominantly feed in colder waters. Special glands in their tube-like nostrils alllow them to ingest seawater. These glands filter out the salt and expel it through sneezing.

Conservation of The Habitats[edit]

Cahows, being a recovering lazarus species, needs special attention in order to support the re-population and growth. Feeding and a proper diet are not the only staple instruments in maintaining the survival and reproduction rate of this species, there a precautions to make sure no Cahow gets lost and that they're comfortable through the regulation of the temperatures in their artificial habitats. With the use of a high solar-powered audio system, preservationists can attract new breeders to a very secure site as well as make sure petrel always know where their home is. The system broadcasts a vocalization of the Bermuda Petrel's call. This system is completely automated and is operational during the night. The preservationists have created two artificial habitats that try to emulate their natural underground burrow. In order to get the correct regulated temperature, a thermometer was placed in the plastic, concrete, and ground burrows and based off the ground's temperature, the other two types of burrows would be regulate to that temperature to ensure survival.

Conservation Issues[edit]

The Bermuda Petrel's re-population has explicitly increased and is approximated that the population doubles every 22 years, but there are still clear-cut inhibitors on its path to recovery. The Petrel's vulnerability has drastically increased because of substantial damage to its habitats and nesting sites by tropical storms and climate changes. With the upcoming increase of category 4 and 5 tropical storms the Petrels face an imminent threat concerning their long-term survivability. Tropical storms also aid to the long-term effect of erosion of their surrounding habitat which puts detriment on the conservation efforts. As a solution, there is research going into finding another suitable area to make the artificial nesting places. 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. Light pollution from a nearby airport and NASA tracking station adversely affects nocturnal aerial courtship.[9]

Another major issue with nests is competition with other birds in the area. To fix this issue, artificial dome nests were created for tropicbirds along areas, not used by the Bermuda Petrel, and by applying wooden baffles over the entrances of petrel burrows. These baffles only allow petrels to enter, keeping the competition of tropicbirds out. Another factor may be that the cahow will have an increased risk of extinction because of restricted ranges, small population sizes, and lower genetic diversity. Additionally, the characteristic philopatry of petrel species may mean that birds continually return to the same high-mortality breeding sites year after year.[10]

Rats also swam to one breeding island in April 2005, but were successfully eradicated within two weeks without loss to the Cahows . 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.[11]


  1. ^ BirdLife International (2012). "Pterodroma cahow". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ "Bermuda's Born-Again Petrels". 
  3. ^ "Overview - Bermuda Petrel (Pterodroma cahow) - Neotropical Birds". Retrieved 2015-10-29. 
  4. ^ "Wingate’s bird boxes give cahows a new home | The Royal Gazette:Bermuda News". The Royal Gazette. Retrieved 2015-10-29. 
  5. ^ "Bermuda Petrel (Pterodroma cahow) - BirdLife species factsheet". Retrieved 2015-10-30. 
  6. ^ Carlile, Nicholas; Priddel, David; Madeiros, Jeremy (2012-03-01). "Establishment of a new, secure colony of Endangered Bermuda Petrel Pterodroma cahow by translocation of near-fledged nestlings". Bird Conservation International 22 (01): 46–58. doi:10.1017/S0959270911000372. ISSN 1474-0001. 
  7. ^ "Bermuda Petrel (Pterodroma cahow) - BirdLife species factsheet". Retrieved 2015-10-30. 
  8. ^ BirdLife International. "News". 
  9. ^ "Bermuda Petrel (Pterodroma cahow) - BirdLife species factsheet". Retrieved 2015-10-30. 
  10. ^ Welch, Andreanna (March 2014). "Phylogenetic Relationships of the Extinct St Helena Petrel, Pterodroma Rupinarum Olson, 1975 (Procellariiformes: Procellariidae), Based on Ancient DNA.". ZOOLOGICAL JOURNAL OF THE LINNEAN SOCIETY. 
  11. ^ "Bermuda Petrel (Pterodroma cahow) - BirdLife species factsheet". Retrieved 2015-10-30. 

Beebe, W. 1932. Nonsuch: Land of Water National Travel Club, New York

Amazing Cahow Facts-The Endemic Bermuda Petrel. Nonsuch Island. LookBermuda. 13 July 2015

“Cahow Fact File.” arkive. Wildscreen Arkive. Web. 26, Oct. 2015.

Lipske, Michael. Bermuda's Born Again Petrels-Conservationists are racing to build up new populations of this island's national bird, once believe extinct for nearly 400 years. National Wildlife Federation.14 January 2013

Madeiros, Jeremy; Carlile, Nicholas and Priddel, David (2011). “Breeding biology and population increase of the Endangered Bermuda Petrel Pterodroma cahow”. Bird Conservation International, 22, 35-45

Madeiros, Jeremy, Bob Flood, and Kirk Zufelt. "Conservation and At-sea Range of Bermuda Petrel." North American Birds 67.4 (2014): 546-57. Web.

CARLILE, NICHOLAS, DAVID PRIDDEL, and JEREMY MADEIROS. "Establishment of a New, Secure Colony of Endangered Bermuda Petrel Pterodroma Cahow by Translocation of Near-Fledged Nestlings." Bird Conservation International 22.1 (2012): 46-58. ProQuest. 30 Oct. 2015 .

MADEIROS, JEREMY, NICHOLAS CARLILE, and DAVID PRIDDEL. "Breeding Biology and Population Increase of the Endangered Bermuda Petrel Pterodroma Cahow." Bird Conservation International 22.1 (2012): 35-45. ProQuest. 30 Oct. 2015 .

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