Bermuda Petrel Pterodroma cahow

Edward S. Brinkley and Kate Sutherland
Version: 2.0 — Published November 16, 2020

Conservation and Management

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Conservation Status


Effects of Human Activity

The earliest accounts of human exploitation of Bermuda Petrels come from the ship logs of Spanish sailors. In 1603, Diego Ramírez, the captain of a Spanish galleon driven by a storm to take harbor in Bermuda, wrote that his crew was able to take 4,000 petrels per night in a single site with ease and that they enjoyed eating them (English translation in 24). These and other Spanish seafarers, who used Bermuda in the early 1500s as a waypoint during raids on the empire of the Incas and others, left hogs on the island, in order to reprovision themselves with pork during their voyages.

William Strachey (1610), then Secretary-Elect for the colony of Virginia, wrote that by the time of the wreck of the English vessel Sea Venture in 1609, nesting petrels were confined to "those ilands which are high and so farre alone in the Sea that the Wilde Hogges cannot swin ouer them." Strachey also wrote (on or around 15 July 1610) that English sailors, selectively culling the fattest individuals, took as many as 240 petrels in 2 hours, mostly by standing on the shore with arms outstretched and calling or singing, which apparently attracted the birds, as did the use of brushwood torches in the evening (34). Strachey noted that the sailors harvested the petrels' eggs in abundance in January. The birds' tameness made them easy to catch; one observer cited in the Historye of the Bermudaes, 1609-1622, wrote: "How monstrous it was to see ... how many of those poore silly creatures, that even offered themselves to the slaughter, were tumbled down into their bottomless mawes."

Less than a decade after Strachey's account, Bermuda Petrel went undetected in Bermuda, and that status did not change until Louis L. Mowbray found a Bermuda Petrel in a rocky crevice on Gurnet Rock, near Castle Island, on 22 February 1906 (11; erroneous date of 20 February given by Beebe [24]).

After the destruction of most of the population of Bermuda Petrel by human settlers and human-introduced mammals in the sixteenth and early seventeenth centuries, the greatest human-generated threat to the survival of this species came in the middle twentieth century, during the height of the production and proliferation of organochlorine pesticides, especially DDT. These toxins were concentrated rapidly through the food chain and caused thinning of egg shells in Bermuda Petrel and many other aquatic birds and birds of prey, which resulted in complete reproductive failure in the species, noted very soon after Bermuda Petrel had been rediscovered (35). The problem has abated only with the banning of DDT in North America in 1972.

Gadfly petrels that are nocturnal on the breeding grounds often are disoriented by bright lights, including fires, at night (36, 37); the reasons for this disorientation are not known. Light pollution from the nearby Bermuda International Airport (Kindley Field), and especially from the down-range satellite tracking station built on Cooper's Point by the National Aeronautics and Space Administration (NASA) in the late 1960s, illuminated all the Bermuda Petrel nesting islets by 1976 and appeared to reduce nesting activity (and apparently causing abandonment of one or more islets; 30), as well as posing a threat of attraction to the many hazards around these facilities, including towers and guy-wires. The situation was resolved amicably in the late 1970s when these facilities agreed to turn off their lights (38). The lighthouse at St. David's, still in operation, has claimed several Bermuda Petrels over the years.

At sea, similar hazards could be posed by ship traffic but especially by wind turbines and petroleum extraction operations, many of which have been proposed for waters of the western North Atlantic where Bermuda Petrels are known to occur.

The population growth of Bermuda Petrel will certainly be limited by mortality associated with landfalling tropical cyclones, which are known to kill other North Atlantic gadfly petrels in numbers (39, 40) and which are predicted to increase as a result of warming oceans and atmosphere. In the recent past, hurricanes have destroyed large numbers of artificial and natural burrows, as during Hurricane Fabian of September 2003 (41), in which nearly all of the concrete burrows were washed away and had to be refabricated. Population growth also will be limited by a reduction in potential nest sites because of rising sea levels (many of the current nesting islets are close to current sea level). Almost all of Bermuda's land area has been developed, and almost all potentially suitable nesting areas would expose petrels to predations of introduced and domestic mammals and to introduced, predatory Cane Toads (Rhinella marinus). As Murphy and Mowbray (5) wrote: "The once spacious nesting grounds of this sea bird at Bermuda are, to all practical intents, permanently destroyed." In the middle twentieth century, Cooper's Island, where Bermuda Petrels had once nested in abundance and which might have served as a restored refuge like Nonsuch, was joined to the main island in order to create more space for the current airport and adjacent facilities. Had Cooper's Island been left untouched, a restoration and recovery project there might have supported many thousands of nesting Bermuda Petrels. Currently, there is no Bermudian island except Nonsuch available for an expanding petrel population; Castle Island is maintained for tourism because of the well-preserved fortress ruins there.

In addition to the myriad negative effects of human activity on Bermuda Petrels, there have been positive effects, almost entirely the work of a handful of biologists and conservationists, chief among them David B. Wingate and Jeremy Madeiros, and their support teams over the past 60 years. What follows is a very brief summary, by year, of the conservation status of Bermuda Petrel, including notes on numbers of established pairs, on numbers of successful fledglings, and on various conservation measures taken to aid the birds in their struggle to survive. Because the nesting season for Bermuda commences in the autumn of one calendar year and concludes in the spring of the following year, the years in the Timeline below indicate first the results at the close of the nesting season (June), when data are compiled on nesting success, and then the returning number of nesting pairs in the following autumn of that calendar year. Because counts of nesting pairs are taken throughout the nesting season, beginning in autumn, published counts often vary, and Audubon newsletters on Bermuda often published a lower or higher count than the final/official count, determined near the end of the breeding cycle (J. Madeiros, personal communication). The counts below are considered correct, and we provide some information on discrepancies in the literature as well.



Seven pairs are found by the Murphys, Mowbray, and Wingate in January and February. The birds handled are noted to be mostly calm during handling, and one bird is banded with a U. S. Fish & Wildlife Service aluminum band. In the extraction of one bird from a burrow, an egg is broken. Four pairs have eggs that hatch. Mowbray later discovers all four chicks dead, killed by returning tropicbirds in search of nest sites. The search team suspects that the petrel population could be larger, with perhaps as many as 18 pairs. The figure of "18 pairs" is abundantly cited in the literature, incorrectly, as the actual number of nesting pairs in 1951 and subsequent seasons.


Seven pairs continue.


Seven pairs continue. From New York, Dr. Richard Pough (American Museum of Natural History) and Richard Thorsell visit Bermuda and devise and install tropicbird-excluding baffles at burrow entrances (42).


Seven pairs continue. One chick survives to fledge, apparently protected from tropicbirds by the baffle. Thorsell and Mowbray end their collaboration, and use of baffles is discontinued for a time.


No data.


No data.


Seven pairs persist. In June, David B. Wingate returns to Bermuda, having graduated from Cornell University. He is employed by Bermuda Aquarium and begins vigorous program to install effective baffles at burrow entrances and also to dig artificial burrows.


In spring, aided by Wingate's burrow baffles, all four chicks that hatch survive to fledge. In autumn, seven pairs return, but only two of these pairs lay eggs.


In spring, the two chicks survive to fledge. In autumn, nine pairs appear, indicating that for the first time in almost a decade, new pairs (two) were attempting to nest. For the first time, one of Wingate's artificial burrows (which have no baffle) is occupied by a Bermuda Petrel (26).


Eighteen pairs of petrels return to nest in the fall. Wingate organizes and implements standard protocols for the official Cahow Recovery Project, which includes monitoring of all nesting pairs and their young, periodic eradication of rats on nesting islands, construction of artificial burrows, and exclusion of tropicbirds from all nest sites. A no-handling policy is strictly enforced, so that the birds' chances being injured are minimized.


In spring, 13 chicks survive to fledge. In autumn, 18 pairs return to nest. Wingate notes that for the first time, 100% of nesting birds in natural burrows are protected by baffles.


In spring, eight chicks survive to fledge. In autumn, 17 pairs return to nest.


In spring, eight chicks survive to fledge. In autumn, 17 pairs return to nest. Wingate and family take up residence on Nonsuch Island (5.8 hectares). Wingate begins multi-decadal project to remove all introduced flora and fauna from Nonsuch and return the island to its precolonial state, with the ultimate goal of having a large population of nesting Bermuda Petrel population as well (see 43).


In spring, seven chicks survive to fledge. In autumn, 18 pairs return to nest.


In spring, eight young survive to fledge. In autumn, 21 (some sources indicate 24) pairs return to nest.


In spring, only six young survive to fledge, leading to suspicions, later confirmed, that the much lower rate of successful hatching could be connected to organochlorine insecticides. In autumn, 21 (some sources indicate 24) pairs return to nest. In this year, a conservation unit was established in the Department of Agriculture and Fisheries, and Wingate was appointed the island's Conservation Officer.


In spring, eight chicks survive to fledge. In autumn, 24 (some sources indicate 26) pairs return to nest. Wingate takes five unhatched eggs and several dead Bermuda Petrel chicks to Charles F. Wurster, Jr., of the State University of New York at Stony Brook. High levels of DDE residues are found in both eggs and chicks.


In spring, eight chicks survive to fledge. In autumn, 24 (some sources indicate 26) pairs return to nest.


In spring, eight chicks survive to fledge. In autumn, 22 (some sources indicate 18 pairs) return to nest.


In spring, six chicks survive to fledge. In autumn, 24 pairs return to nest.


In spring, 13 young survive to fledge. Wingate raises an abandoned chick to fledging as well (44). In autumn, 26 pairs return to nest. For the first time since early colonial times, courting Bermuda Petrels can be seen and heard from Nonsuch Island.


In spring, 16 (some sources indicate 17) young survive to fledge. In autumn, 25 (some sources indicate 26) pairs return to nest. Wingate reintroduces the native bermudianus subspecies of White-eyed Vireo (Vireo griseus) to Nonsuch Island. DDT is banned in the United States.


In spring, 12 young survive to fledge. In autumn, 25 pairs return to nest.


In spring, 12 chicks survive to fledge. In autumn, 25 pairs return to nest. Wingate estimates that the world population of Bermuda Petrel, including the subadults at sea, may be near 100 individuals, for the first time in three centuries.


In spring, 11 chicks survive to fledge. In autumn, 26 pairs return to nest.


In spring, 11 chicks survive to fledge. In autumn, 27 pairs return to nest. Light pollution from the airport and NASA tracking station appears to inhibit nesting activity. Wingate begins talks with representatives from both facilities. Wingate reintroduces Yellow-crowned Night-Herons (Nyctanassa violacea) to Nonsuch Island.


In spring, 14 chicks survive to fledge. In autumn, 27 pairs return to nest.


In spring, 15 chicks survive to fledge. In autumn, 27 pairs return to nest.


In spring, 16 chicks survive to fledge. In autumn, 28 pairs return to nest.


In spring, 17 chicks survive to fledge. In autumn, 29 pairs return to nest.


In spring, only 10 chicks survive to fledge. In autumn, 32 pairs return to nest.


In spring, 21 young survive to fledge. In autumn, 35 pairs return to nest.


In spring, 20 chicks survive to fledge. In autumn, 34 (some sources indicate 35) pairs return to nest.


In spring, 18 chicks survive to fledge. In autumn, 35 (some sources indicate 36) pairs return to nest. David Wingate hires local biologist Jeremy Madeiros as his assistant.


In spring, 21 (some sources indicate 22) young survive to fledge. In autumn, 40 pairs return to nest.


In spring, 16 chicks survive to fledge. In autumn, 41 pairs return to nest.


In spring, 24 chicks survive to fledge. In autumn, 41 pairs return to nest. New lights are installed at the U.S. Naval Air Station near the Castle Harbour Islands, and over the next several nesting seasons, it becomes clear that the lights are inhibiting courtship of petrels.


In spring, 22 chicks survive to fledge. In autumn, 45 pairs return to nest.


In spring, 28 young survive to fledge. In autumn, 43 pairs return to nest. In autumn, Hurricane Dean struck Bermuda as a Category 2 storm 7 August 1989, damaging Bermuda Petrel burrows as well as nest sites of White-tailed Tropicbirds (Phaethon lepturus; 45).


In spring, 18 chicks survive to fledge. In autumn, 41 pairs return to nest (46 indicates 43 pairs). Hurricane Hugo makes landfall at the Isle of Palms, near Charleston, South Carolina on 22 September 1990 as a Category 4 hurricane, and it becomes clear that many seabirds perished in the storm, both at sea and on land. The storm may have killed multiple Bermuda Petrels, as reflected in the decrease in nesting pairs in autumn 1991 (47). In November 1990, the U.S. Naval Air Station agrees to turn off the lights at night, so that petrels will be able to court normally (46).


In spring, only 19 chicks survive to fledge (46). In autumn, 43 pairs return to nest (48). During September and October, more artificial burrows are built, and a 7-m seawall is also built to deflect storm surge around several of the lower-lying nest burrows. This prevented the flooding of active nests when Tropical Storm Grace struck Bermuda 26 October 1991 (48).


In spring, 23 young survive to fledge (Wingate 1992). In autumn, 44 pairs return to nest (47).


In spring, 21 young survive to fledge (47). Of the known causes for nesting failure, one chick dies on hatching and one a few days later; one is found starved; one has to be euthanized because of a badly deformed wing; and apparently for the first time since 1961, one chick is killed by a White-tailed Tropicbird (47). Fifteen new artificial burrows, requiring seven tons of concrete, are built on the western breeding islands (47). In autumn, 45 pairs return to nest.


In spring, 21 chicks survive to fledge. In autumn, 49 pairs return to nest (49, 50, 51).


In spring, 24 chicks survive to fledge (51), but only 22 of those are considered healthy; one departs in "marginal" condition, and one is found dead before departure (50). The final count of successfully fledged young is 23 (J. Madeiros, personal communication). Among the healthy birds to depart was one that had been found attacked by a White-tailed Tropicbird 29 March; Wingate applied a splint to the mandible with CrazyGlue, and the bird recovered, departing on the night of 24/25 May (50). Storm surge from Hurricane Felix badly damages about 50% of Bermuda Petrel nest sites (22 in all) on 15 August, along with many nest sites of White-tailed Tropicbirds (50, 45); the storm was briefly a Category 4, but winds around Bermuda peaked at about 80 knots. In autumn, 52 pairs return to nest (52).


In spring, 26 chicks survive to fledge (52). In autumn, 53 pairs return to nest (Wingate 1997d). In 1996, the unhatched eggs from 1995 and 1996 are tested for PCB and pesticide levels (53).


In spring 29 chicks survive to fledge, including one abandoned chick that is hand-reared by Andre Raine and Giselle Laxalt, with the bird eventually departing a makeshift burrow on Nonsuch Island 23 July 1997 (almost two months later than average). In autumn, 55 pairs return to nest, and four new pairs are noted to be prospecting nest sites (3, 54). In November, dedicated seawatches from Cooper's Point on Cooper's Island produce reasonably good views of flying Bermuda Petrels (with a spotting scope), offering an alternative to the small-boat pelagic trips that began in 1993 (3).


In spring, 29 chicks survive to fledge. Thirty-two chicks survive to fledging age, but one has a deformed wing and is euthanized (specimen sent to the British Natural History Museum at Tring per 55); one does not leave the burrow, despite normal feeding by adults; and one departs the burrow on the night of 20/21 June 1998 but is found dying in Castle Harbour by Mark Whayman (on the sailboat Sand Dollar) (54). In autumn, 56 pairs return to nest, and the number of new colonizing or prospecting pairs increases from four in 1997 to seven in 1998, a significant increase.


In spring, 27 chicks successfully fledge, one of those an underweight chick that was hand-reared to fledging by Jennifer Gray and Patrick Talbot at the Bermuda Aquarium and Zoo. Another hand-reared bird was placed back in its burrow 2 July but was found dead of heatstroke that evening. On 20-21 September 1999, the storm surge associated with the passage of Hurricane Gert overwashes two of the four Cahow nesting islets, causing damage to 30% of the nest sites, which must be repaired before the start of the nesting season; thankfully, the repairs made after damages from Hurricane Felix in 1995 prevent more severe damage (56). In autumn, 53 pairs return to nest, but this count is later revised to 59 pairs (J. Madeiros, personal communication).


In spring, 25 young survive to fledge, although 2 of these were rehabilitated at the Bermuda Aquarium, Museum, and Zoo before being released (57). In all, 32 chicks hatch, but four die soon after hatching and three later in their development. Probably because of mortality due to the intense Atlantic hurricane activity in 1999, three pairs failed to return to nest, and three individual adults (part of established nesting pairs) also fail to return. Also this year, David Wingate retires as Government Conservation Officer, and Jeremy Madeiros, who has worked with the petrels for 17 seasons, succeeds him in the position. In autumn, 60 pairs return to nest.


In spring, 32 young survive to fledge. In autumn, 65 pairs return to nest (58; prematurely published data elsewhere indicate 59 pairs).


In spring, 35 or 36 young survive to fledge (58). Jeremy Madeiros initiates a program to fit all Bermuda Petrels with aluminum leg bands (5.5 mm bands made of an alloy called "incoloy"), in order to estimate survivorship, population, and other aspects of breeding ecology. These bands are specially made for the petrels by Porzana, Ltd., and in the first season, 30 fledglings and 10 adults are banded (58). Madeiros also initiates a program of weighing chicks regularly to gather data on growth rates and also to help in identifying underweight/malnourished birds that might require rehabilitation (58). In time for the returning adults in October, Madeiros and crew erect 12 new burrows (required 7000 pounds of concrete) on the nesting islets, to augment the nearly 70 built there since the 1960s (59). In autumn, 70 pairs return to nest (60), including five new pairs, and five new nest sites are prospected, including two of the 12 newly built artificial nesting burrows, one of which is used for nesting by a new pair (61). More adults and fledlgings are banded during the season, bringing the total of banded petrels to 79 (60).


In spring, 40 young survive to fledge (60). In autumn, 65 pairs return to nest. A Category 3 storm, Hurricane Fabian, overwashes three of the four breeding islets 25 September 2003, with 35-foot waves damaging or destroying a significant number of nest burrows, which need to be reconstructed or replaced in the span of a very stormy five weeks (62).


In spring, 29 young survive to fledge (63). In autumn, 71 pairs return to nest, including six new pairs (63).

In 2004 and again in 2005, using playback of adult courtship calls recorded by Cornell University's Macaulay Library of Natural Sounds (64), efforts are made to attract adult Cahows to a new artificial burrow complex built on a more elevated section of the islet on which so many of the low-lying burrows had been destroyed by Hurricane Fabian.

Also in 2004, an ambitious, much larger project of translocation is finally realized, after many years of study and planning: 14 older chicks are moved to Nonsuch Island, where they are fed and monitored every other day until departure, with all 14 fledging successfully between 27 May and 10 June (62).


Black rats (Rattus rattus) swim to one breeding island in April but are successfully eradicated (no loss of chicks). In spring, 35 young survive to fledge. Of these, 21 chicks are translocated from smaller, low-lying islands to Nonsuch Island between 8 May and 2 June, with all 21 fledging successfully 21 May through 15 June (63. In all, 35 young survive to fledge. In autumn, 76 pairs return to nest.

As in 2004, in an effort to attract adult Bermuda Petrels displaced from low-lying nest burrows destroyed by Hurricane Fabian to a new artificial burrow complex built on higher ground, an audio-lure system (broadcasting courtship vocalizations) is again placed among the new burrows (63), and paired adults that are attending areas where burrows have been destroyed are captured and placed together in the new burrows. By March 2005, three pairs utilize burrows in the new complex (63). Twenty-eight chicks are banded this season, bringing the total number of banded petrels to 183 (63).


In spring, 36 young survive to fledge. In autumn, 80 pairs return to nest (J. Madeiros, personal communication).


In spring, 39 young survive to fledge (J. Madeiros, personal communication). In autumn, 85 pairs return to nest, and six new pairs are seen prospecting (65). The audio-lures are again used to attract petrels to Nonsuch Island so that they might prospect higher nest sites there rather than at original nesting islets, and some of the translocated birds are seen returning and prospecting near their burrows (65). Of the 79 chicks translocated chicks to Nonsuch Island in the four seasons of the project, only one fatality is recorded (65, 66).


The translocation project to Nonsuch Island continues, with a total of 105 translocated chicks since 2004, 102 of which have fledged successfully (65). In March, four chicks are killed by one or more Black Rats (Rattus rattus; 65), but 40 young fledge from 85 nest sites. In autumn, 86 pairs return to nest.

Between 2002 and 2007, Madeiros and team band 171 fledglings, and as of 2009, 31 are confirmed to have returned, representing cohorts from the four nesting seasons 2002 through 2005 (65).


In spring, 48 young survive to fledge. In early 2009, the first adult-fed Bermuda Petrel in four centuries hatches on Nonsuch; the bird, named "Somers" in honor of Admiral Sir George Somers, the first governor of Bermuda, fledges successfully in June 2009, a realization of Wingate's lifelong dream (67). Of the 105 Bermuda Petrel chicks translocated to Nonsuch 2004-2008, all but three fledge to sea successfully (67). In autumn, 92 pairs return to nest, and at least 10 more potential new nest sites were observed being prospected by petrels. Fourteen individuals fledging from Nonsuch Island after translocation (in 2005 and 2006) were observed in 2009 returning to the island and entering artificial burrows. In order to investigate movements of adults at sea, a new program is begun to outfit petrels with Lotek geolocational dataloggers, which weigh only 4.7 grams and whose data on movements of petrels can be downloaded without removing them from the birds (14).


The return of translocated petrels to Nonsuch Island is remarkable, involving at least 22 translocated individuals and two non-translocated birds, indicating that a sufficient nucleus of translocated birds exists for attracting new birds to the colony, which involves seven nesting pairs this season (21). In spring, 52 young survive to fledge. Among these is the second adult-fed Bermuda Petrel to fledge on Nonsuch, named "Bermudiana," whose maiden departure for the ocean occurs on the evening of 7 June. In all, 32 Bermuda Petrels are fitted with leg bands during the 2009-2010 breeding season, bringing the total number of petrels banded since 2002 to 374, with 111 of these banded as adults (right leg), 263 banded as nestings (left leg).

Of the 40 nests with nesting failures recorded, two involve chicks that died during hatching and seven that died later in the development; seven eggs are found pipped or broken; 11 eggs are infertile or do not hatch; eight eggs are buried or knocked off the nest; two eggs are washed off the nest by storm waves; and two eggs disappear late in incubation, perhaps taken by Land Hermit Crabs (Coenobita clypeatus; 21). In autumn, 98 pairs return to nest, a record-high number for modern times (68, 69).


The 98 pairs produce 56 chicks that fledge successfully, a breeding success rate of 57.14%. Prospecting or pre-breeding activity is recorded at six new sites, three of those on Nonsuch Island (68). In all, 22 translocated birds return to Nonsuch, while 8 other translocated birds return to their natal islets. As hoped, the translocated birds that return to Nonsuch have attracted other, non-translocated birds, and the expectation is that the island will become the species' most important nesting area in the future (68).

Of the 42 nests with nesting failures recorded, two involve chicks that died shortly after hatching and four that died later in the development; 15 eggs are found pipped or broken; 12 eggs are infertile or do not hatch; two eggs are buried or knocked off the nest; two eggs disappear during the incubation period; one egg is washed off the nest by storm waves; one egg is broken during a nest check; and two chicks disappear shortly after hatching, perhaps taken by Land Hermit Crabs (Coenobita clypeatus; 68).

A record-high (since the 1600s) 101 pairs of Bermuda Petrels return to nest in autumn (70, 71).


In the 2011-2012 season, 2 chicks are abandoned by their parents and are taken into care to feed them and enable them to mature and accumulate enough fat reserves to fledge successfully out to sea. One is moved from a nest burrow on Horn Rock to an empty artificial nest burrow at the translocation site on Nonsuch Island, but that bird is too emaciated when found and does not survive. The other chick, in a burrow on Nonsuch Island, recovers and fledges successfully. Overall, the newly established colony on Nonsuch Island has 10 pairs that lay eggs, from which seven chicks hatch and eventually fledge. In total, at least 26 adult Bermuda Petrels are confirmed as returning to Nonsuch Island in the 2011-2012 season (and a total of 41 of the 102 translocated birds documented to have returned since the program began), with 13 pairs nesting on Nonsuch in total (70, 71). In autumn, 105 pairs return to nest.


The 105 pairs produce 53 chicks that fledge successfully, a breeding success rate of 50.5%. Remarkably, three nesting pairs were found on a new island, Southampton Island, only 80 m from Horn Rock, where there were 37 nesting pairs in 2012-2013 (15). An infrared "burrow cam" was installed in a nest burrow, allowing people all over the world to view weekly video of a chick nicknamed "Backson," documented from hatching through fledging and departure out to sea. A second translocation of 14 chicks to Nonsuch Island was commenced at the B site, on the south hill overlooking the south beach area of the island; 12 of these birds fledged successfully. An apparent Great Horned Owl (Bubo virginianus) reached Bermuda in autumn 2012 and on 27 November was found to have killed and eaten at least two, possibly three adult Bermuda Petrels (15). Of the 46 documented nest failures, 2 involved chicks that died in hatching, 12 chicks that died later in development, 11 broken or pipped eggs, 17 non-hatching or infertile eggs, and 4 eggs buried or knocked off the nest (15). In autumn, 108 pairs return to nest.


In spring, 59 young survived to fledge, a record count. In autumn, 111 pairs return to nest.


The 111 breeding pairs, including 15 pairs at the Nonsuch colony, produce 53 chicks that successfully fledge (9 from Nonsuch), a success rate of 47.3%. During the nesting 2014-2015 nesting season, Madeiros conducts conservatively 2,000+ health checks, on average checking every chick in the colony every 2 days, often under very challenging weather conditions. In autumn, 115 pairs return to nest.


In spring, 56 young survive to fledge (J. Madeiros, personal communication). Hurricane Karl and Hurricane Nicole both struck Bermuda in autumn 2016. According to Jeremy Madeiros (personal communication), the latter storm "made a direct hit on Bermuda on 13 October as a Category 3 cyclone, with the eye passing directly over the island around midday. The storm had lost some strength in the hours before landfall, and it struck during low tide, minimizing the storm surge. Easterly winds (blowing right on the nesting islands) were sustained at 103 mph, gusting to 122-136 mph during the first half of the hurricane, followed by passage of the storm's 30-mile diameter eye, which lasted for over an hour, with winds dropping to 14-16 mph." Jeremy Madeiros recorded pressure at 28.31 in. during the eye passage. "The winds then switched to the northwest and increased to 85-93 mph for the next few hours before diminishing as the storm moved away toward the northeast. A total of 6.77 inches of rain was recorded. Nicole was less damaging than Hurricane Gonzalo of 2014, also a direct hit with the eye passing over, when sustained winds reached 110 mph with gusts to 144 mph and central pressure at 27.98 in. Gonzalo hit on 17 October and killed five pairs of petrels that had already returned to the nesting islets. By comparison, Nicole caused minimal damage to the nesting islands and appeared to affect none of the nesting pairs. Part of this is due to Nicole not being as intense as Gonzalo, part to it hitting at low tide, and part to timing (most Bermuda Petrels do not start returning until after the 15-20 October, and the few days can make a huge difference). The Nonsuch colony was completely unaffected by any of the recent hurricanes. The second translocation project at the B site at Nonsuch is going well with almost 60 chicks fledged over the past years, with the first returns last season. Damage from this storm was minimal, with just a few of the nest lids dislodged from two of the lower breeding islets, and about half of the nest burrows needing rocks and debris cleared from entrances and nest chambers." In autumn 2016, returning birds formed 117 pairs that would nest in the 2016-2017 season.


The pairs that returned in 2016 produced a record-high 61 successful fledglings in 2017. Through partnership with the Cornell Lab, infrared “nest-cams” provided the public with detailed viewing via internet (www.nonsuch.com) of the breeding activity of a pair of Bermuda Petrels in an underground burrow on Nonsuch Island, including the hatching of a chick on 4 March and the development of the chick until it fledged out to sea around 6 June. In fall 2017, returning birds formed 124 pairs that would nest in the 2017-2018 season.


The pairs that returned in 2017 produced a record-high 71 successful fledglings in 2018. The first nesting colony on Nonsuch Island, established by the translocation of chicks between 2004 and 2008, continued to grow, with 18 pairs established in nest burrows there in the 2017-2018 season. The second nesting colony on Nonsuch, established by translocation of chicks between 2013 and 2017, had two breeding pairs in the 2017-2018 season. Through partnership with the Cornell Lab, infrared “nest-cams” continued to provide detailed viewing via internet (www.nonsuch.com) of the breeding activity of a pair of Bermuda Petrels, including courtship and mating activities by the adults, and the hatching and development of the chick until it fledged out to sea around 2 June. In fall 2018, returning birds formed 131 pairs that would nest in the 2018-2019 season.


The pairs that returned in 2018 produced a record-high 73 successful fledglings in 2019. In fall 2019, returning birds formed 134 pairs that would nest in the 2019-2020 season. This season also saw the launch of major initiatives by international teams of researchers. Letizia Campioni of Italy and Monica Silva of Portugal led teams in January-February 2019 that fitted 22 incubating adult Bermuda Petrels with GPS units in order to map foraging areas during incubation. In a second project, Carina Gjerdrum of Canada and André Raine of Hawaii fitted 6 adult Bermuda Petrels with longer-lived GPS units in April, to study the foraging range of adults provisioning young. A research project conducted by researchers including senior conservation warden Jeremy Madeiros involved collection of blood and feather samples from 90 adults in order to identify the trophic niche of foraging Bermuda Petrels during the breeding season as well as to determine the presence of Persistent Organic Pollutants integrated with diet (DDT, DDE, PFOs, PCPs, etc.).

2020 and beyond

For details on the 2019-2020 and later nesting seasons, please consult: https://environment.bm/cahow-recovery-programme.

Recommended Citation

Brinkley, E. S. and K. Sutherland (2020). Bermuda Petrel (Pterodroma cahow), version 2.0. In Birds of the World (T. S. Schulenberg, B. K. Keeney, and S. M. Billerman, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.berpet.02