Bermuda Petrel

Few birds carry a story like the Bermuda Petrel, known to islanders as the cahow. A medium-sized gadfly petrel and the national bird of Bermuda, it spends almost its entire life over the open North Atlantic, touching land only in darkness to breed. Its unearthly night calls once echoed across the islands in enormous numbers and gave rise to sailors' tales of haunted, devil-infested shores.

Then it vanished. After Bermuda was settled in the early 1600s, hunting for food and the arrival of rats, cats, dogs and pigs erased the visible population within a few decades. For roughly 300 years the cahow was written off as extinct, one of the earliest human-caused bird extinctions in the New World. Its rediscovery in 1951, when a small cluster of nesting pairs turned up on tiny rocky islets in Castle Harbour, made it one of the most celebrated Lazarus species on Earth, an animal found alive long after being declared gone. Decades of painstaking conservation have since coaxed the population back from the brink, though the cahow remains one of the rarest seabirds in the world.

The Bermuda Petrel is a long-winged, medium-sized gadfly petrel built for a life at sea. Most observers encounter it far offshore in the North Atlantic, where it wheels over the waves on stiff, bowed wings. On land it is strictly nocturnal, so daytime views near the colony are essentially impossible. Look for the clean dark-above, white-below pattern typical of Pterodroma petrels, combined with a fast, bounding, high-arcing flight.

Male vs. female

Males and females look alike in the field. Like most petrels, the cahow shows no visible plumage difference between the sexes, and pairs cannot be told apart by eye. Males average very slightly larger with marginally longer bills, but this is only measurable in the hand and is not useful for a birder at sea or a visitor at the colony. Researchers instead identify individuals by leg bands and, at the nest, by burrow occupancy rather than by any external clue to sex.

Juveniles

Freshly fledged cahows closely resemble adults, wearing the same dark-above, white-below pattern from their first flight, so age is hard to judge on a bird at sea. The clearest signs of youth are seen only at the colony: a downy grey chick fattened in the burrow, and freshly fledged juveniles with crisp, neatly edged wing feathers before wear sets in. After leaving Bermuda, young birds spend several years roaming the open Atlantic before returning to breed, and they do not attain full adult breeding readiness until around three to six years of age.

At sea the cahow is silent, as gadfly petrels generally are away from land. All of its voice belongs to the night at the colony. Returning birds give the eerie, moaning, wailing cries that inspired the onomatopoeic name cahow, a sound early settlers described as ghostly and disturbing when whole hillsides of petrels called at once. Courting pairs and burrow visitors deliver these drawn-out moans and softer crooning notes in the darkness, both in flight overhead and from inside the nest chamber.

Because the birds come ashore only after dark and nest on strictly protected islets, these calls are now heard by very few people. What was once one of the loudest night sounds in the North Atlantic is today a rare privilege, experienced mainly by conservation staff and a handful of visitors to the nesting islands.

Breeding is confined to a tiny area of Bermuda: a handful of small, rocky islets in Castle Harbour on the eastern end of the archipelago, plus the restored colony on Nonsuch Island. The total nesting habitat amounts to only about a square kilometre, making the cahow's breeding range one of the most restricted of any seabird.

Away from land the picture is very different. Outside the breeding season, and even between foraging trips during it, cahows range enormously across the open North Atlantic. Satellite tracking has shown birds foraging north and east toward the waters off the eastern United States, out to the mid-Atlantic and toward the Azores and the North Atlantic Current, covering thousands of miles between visits to the nest. They come to land only to breed and are almost never seen from shore, which is why sightings away from Bermuda are prized events on deep-water pelagic trips.

The Bermuda Petrel feeds far out over deep water, taking small squid, small fish and crustaceans caught at or just beneath the surface. Like other gadfly petrels it forages on the wing, snatching prey in brief dips and shallow plunges rather than diving deep, and it likely follows productive fronts and eddies where prey concentrates near the surface.

Because feeding areas can lie hundreds of miles from the colony, adults make long foraging journeys and return to deliver energy-rich meals to their single chick. During the chick-rearing months a parent may be away for many days at a time, then arrive after dark to feed the young bird a concentrated store of squid and fish before heading back out to sea.

Cahows nest in burrows and natural rock crevices on their islets, and now readily adopt the artificial concrete burrows built by conservationists to replace scarce natural sites. Pairs are long-lived and faithful both to their mate and to their burrow, returning to the same nest year after year. A single white egg is laid, usually in January, following a pre-laying exodus during which both adults spend weeks at sea building the reserves needed for breeding.

Both parents share the long incubation, which lasts roughly seven to eight weeks, and then take turns delivering food to the chick over several months. The young bird eventually fledges out to sea alone, typically around late spring, and does not touch land again for several years until it returns to prospect for a burrow and a mate of its own. This slow, single-chick cycle means the population can only ever recover gradually, which is why every nesting pair matters so much.

This is not a backyard bird, and it cannot be attracted with feeders or nest boxes. The cahow lives its whole life over the open ocean and breeds only on strictly protected, off-limits islets in Bermuda. Realistically, seeing one means going where they are, at sea, and going through official channels. Here is honestly how and where to have a chance.

• Book a deep-water pelagic birding trip out of Bermuda, the only practical way for the public to see a cahow in flight over its home waters; these trips are timed to the breeding season and run by experienced local guides.
• Visit the Nonsuch Island living museum or a Castle Harbour conservation program when berths are available, as access to the nesting islets themselves is tightly restricted to protect the birds.
• Watch the CahowCam livestream, an infrared camera placed inside an artificial burrow that streams incubation and chick-rearing online, offering intimate views no in-person visit could match.
• Time any attempt to the breeding season roughly November through June, when adults are present around Bermuda; outside these months the birds are dispersed far across the Atlantic.
• Support the Bermuda cahow recovery program and follow official updates, since responsible tourism and donations directly fund the burrows and predator control that keep the species alive.
• On any Bermuda pelagic, learn the gadfly-petrel flight style in advance, high, fast, bounding arcs on stiff wings, so you can pick a cahow out from shearwaters and other seabirds.

• Black-capped Petrel: Larger Atlantic gadfly petrel with a bolder white collar and a broad white rump patch; the most likely confusion species in western Atlantic waters.
• Fea's Petrel: Similar dark-and-white North Atlantic gadfly petrel but shows a distinctly darker, greyer underwing and a paler grey tail.
• Manx Shearwater: Another black-and-white Atlantic seabird, but a shearwater with clean black-above, white-below plumage and long, low, stiff-winged glides rather than high arcs.