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 pictured on Bermudian currency. 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 300 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.
Cahows, being a recovering lazarus species, need special attention in order to support recovery and population growth. All nesting and nearby islands are strictly protected as part of the Castle Islands Nature Reserve, and landing by the public is prohibited except by special permission in the company of the conservation officer. This area is also designated as an international I.B.A. (Important Bird Area), in recognition of containing the entire world population of Bermuda petrel, and up to 20% of the North Atlantic population of white-tailed tropicbird. These islands are maintained rat-free by an annual baiting program, and domestic animals are prohibited from landing on all islands in the reserve. In addition, there is an ongoing management program to eradicate non-native invasive plant species on all of the reserve islands, coupled with plantings of native and endemic plant species, many of which are also endangered. Several of the nesting islands are also the subject of an ecological restoration project, to restore them as examples of the terrestrial plant and animal communities once found on, but now largely lost from, the rest of Bermuda.
Cahows typically eat small fish, squid and shrimp-like crustaceans. They also predominantly feed in colder waters. Geolocator studies carried out between 2009 and 2011 confirmed that they primarily forage in two widely separated locations during the non-breeding season (July to October), between Bermuda, Nova Scotia and North Carolina, and to the north and northwest of the Azores archipelago. Special glands in their tube-like nostrils allow them to ingest seawater. These glands filter out the salt and expel it through sneezing.
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. 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 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 between May and June. Cahows mate for life and typically return to the same nest each year.
In a first of its kind, a high school science project engaged in a remote study via live webcam using Cornell Lab's Cahowcam. It described incubation behavior of this species. The study found that sexes shared incubation duties equally; sedentary behaviors of incubating parent included resting (56% of observed time), sleeping with head tucked back (31%), preening (5%), and nest maintenance (3%); nest attentiveness was high, with the egg left unattended only 1.5% of the observed time; and the incubating parent faced the nest entrance 49% of the time. Breathing rates and head shake movements were also measured for the first time in a seabird. Both parents were in the nest together for only 11 of the 55 days (19%) of observations. The egg failed in this study. A parent was observed burying the inviable egg on the 68th day since laying.
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. He undertook work to address various threats to the Bermuda petrel, including the eradication of introduced rats on the nesting islands and nearby islands, and addressed nest-site competition with the more aggressive, native white-tailed tropicbird Phaethon lepturus catsbyii, which invaded petrel nest burrows and killed up to 75% of all chicks. Following the design and installation of specially sized wooden "baffler" burrow entrance covers, which allowed the petrels to enter but excluded the larger tropicbirds, there has been essentially no further chick loss from this cause.
Wingate also initiated the ecological restoration of Nonsuch Island, located near the Bermuda petrel breeding islets. Nonsuch 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 recreate what had been lost, and thousands of endemic and native plants, including Bermuda cedar (Juniperus bermudiana ), Bermuda palmetto palm (Sabal bermudana ) and Bermuda olivewood (Cassine laneanum ), were propagated and planted out on Nonsuch to recreate the original forest ecosystem that once covered Bermuda, but which was almost entirely lost through disease and clearing for agriculture, shipbuilding and residential development. In total, almost 10,000 individual native and endemic plants of over 100 species were planted on Nonsuch starting in 1962, and have since developed into a well-established closed-canopy forest, similar to early accounts of what was found on Bermuda by the earliest settlers in the 1600s. Wingate's goal was to restore the habitat on Nonsuch Island so that it could eventually serve as a viable nesting site for the species.
Even after retirement, Wingate designed and donated artificial plastic nest boxes to the Cahow Recovery Project, funded by the Bermuda Audubon Society. These nests were an effort made toward assisting the recovery of the Bermuda petrel, which normally nest in deep soil burrows or rock crevices but suffered from a shortage of suitable nest sites and soil for the birds to burrow in on the original nesting islets. Artificial concrete burrows have been used for many years to provide additional nesting opportunities for the birds, but are very labor-intensive to construct, requiring 400-800 lbs of concrete each. The new nest boxes were designed to meet the birds nesting needs, and it is hoped that they will assist in the recovery of the cahow for its future survival.
David Wingate retired in 2000, after which Jeremy Madeiros became the Bermuda Government terrestrial conservation officer, taking over the management of the Cahow Recovery Program and the Nonsuch Island Living Museum Project. Madeiros carried out a review of the status of the Bermuda petrel, identifying erosion of the four small original nesting islets due to hurricane damage and sea level rise as the single largest threat facing the species. A banding program for both fledgling and adult petrels was initiated in 2002, and by 2015 had resulted in over 85% of all Bermuda petrels being fitted with identification bands, enabling positive identification of individual birds through their breeding lifespan. Madeiros published a recovery plan for the Bermuda petrel, which provided guidelines and objectives for the management of the species, in 2005.
