The noise comes after dark and it does not sound like a bird. It is a long rising wail with a broken cry at the end of it, delivered from somewhere underground and answered from the air. Sixteenth century sailors who heard it off an uninhabited island in the middle of the Atlantic drew the obvious conclusion, and the Spanish marked Bermuda as the Isle of Devils. They put pigs ashore and mapped it; they never settled it.
The devil was a cahow, and the word is the noise: Bermudians named the bird for the cry it makes. It is a gadfly petrel, about the size of a small gull, dark above and white below, and it spends almost its whole life over open ocean. It touches land only to breed, only at night, and only to go down a hole.
The breeding cycle is why this recovery is counted in lifetimes. A pair returns to the same burrow, lays a single egg between the end of December and the end of January, and incubates it for about fifty three days. The chick hatches from mid February into March and flies in late May or June, and then it does not touch land again for years.
A young cahow spends its first few years continuously at sea before coming back to look for a burrow of its own, and a pair that loses an egg does not lay another that season. One egg a year, from birds that take years to start breeding at all, is the ceiling on how fast the species can recover.
That is a good strategy against hawks and a poor one against people. The birds nested in enormous numbers on an island with no land mammals at all, which meant they had no reason to be wary and nowhere to go. When the English were wrecked here in 1609 and stayed, they found a food supply that made no attempt to get away.
The colonists worked out that a brushwood torch held up at night would pull the birds in off the sea, and then they clubbed them. Pigs put ashore earlier by passing ships dug out the burrows. Rats came off the boats and took the eggs.
By 1616 the Governor, Daniel Tucker, had noticed. He issued a proclamation against the spoil of the cahow, which is one of the earliest attempts anywhere in the New World to protect a wild bird by law, and it is worth being clear about how well it worked. The species was gone from the main islands within a decade and was considered extinct by the 1620s.
It stayed extinct for about three hundred and thirty years, which is long enough that finding it again was not a rediscovery so much as a correction to the record.
On 28 January 1951 an expedition working the bare rock islets in Castle Harbour, led by the American ornithologist Robert Cushman Murphy with the Bermudian naturalist Louis S. Mowbray, pulled a live cahow out of a crevice. A week of searching turned up a handful of occupied burrows spread across three islets. The figure that entered the literature, eighteen nesting pairs, came out of the searching that followed through the decade, and it was still the entire known world population at the end of the 1950s.
The islets they were found on are not much: bare rock a few metres above the water, without soil enough for a burrow. The surviving birds had been nesting in natural crevices in the limestone, which is the only reason any had lasted, and it is also why so few of them were left.
A fifteen year old Bermudian named David Wingate was on the boat that day, brought along because the island already knew him as the boy who knew the birds. He spent the rest of his working life on this one species, became Bermuda's first government conservation officer, and the recovery below is essentially his career and his successor's.
Bermuda's other problem is that the rock keeps eroding and the sea keeps rising, so the number of usable crevices was falling while the population was supposed to be climbing. Everything that followed was an attempt to manufacture nesting ground faster than the Atlantic could take it away.
The first problem was not rats or people. It was another seabird. The white-tailed tropicbird, which Bermudians call the longtail, wants the same kind of hole, arrives later in the season, and will kill a cahow chick to take its burrow.
The answer was a piece of wood with a slot in it, fitted over the burrow mouth and cut to a size a cahow can pass and a longtail cannot. Richard Pough proposed the principle and a researcher named Thorsell settled the dimensions by 1955; Wingate, not knowing that work had been done, derived the same answer again and had bafflers on every known nest by the spring of 1961. The device costs almost nothing to make and it is the single intervention the population curve responds to.
Progress after that was measured one pair at a time. The known population was fifty odd by the time Wingate retired in 2000, which is a little over one additional pair a year across a working life. Every figure in this story is a number of pairs, counted by hand, in a season.
The larger project was Nonsuch. It is a fifteen acre island in Castle Harbour, higher than the nesting islets and long since stripped of everything native, and Wingate moved his family onto it and set about putting the island back. He replanted cedar and palmetto and imported the animals that belonged, with the aim of reconstructing what Bermuda looked like before anyone landed.
He called it a Living Museum and began it in 1963. Something over eight thousand trees and shrubs went into the island by the early 1970s, among them Bermuda cedar grown from the few trees that had survived the scale insects that killed most of the island's cedars in the 1940s.
Then he put the animals back, and where the original was extinct he used the nearest living equivalent. Bermuda's endemic night heron was long gone and the island's land crabs had nothing controlling them, so Wingate introduced the yellow-crowned night heron from Florida. Inside a year he was reporting that land crab made up almost the whole of their diet. The West Indian top shell and the endemic killifish went back too, and the Bermuda skink, which had never left, recovered with the habitat.
Jeremy Madeiros took the work on and made the move the birds could not make themselves. A cahow returns to breed where it fledged, so an adult on an eroding islet will keep nesting on that islet. Between 2004 and 2008 Madeiros carried near fledged chicks across to artificial burrows on Nonsuch and hand fed them until they left, so that Nonsuch was the place they would imprint on and come back to.
The reason he did it when he did was Hurricane Fabian, which went over the nesting islets in 2003 and destroyed around ten of the seventy odd active nests. It made the arithmetic obvious: a single storm on a bad line could take a meaningful share of a species that existed in one place, a few metres above sea level.
One hundred and five chicks were moved and one hundred and two fledged, on the Government's figures; the peer reviewed paper Madeiros co-authored gives 104 and 101. The first of them came back in February 2008. The first egg on Nonsuch in something like four centuries was laid in January 2009, and the chick flew that June. A second translocation ran from 2013 to 2017 and started the second colony, which is why the island's cahows are always spoken of in the plural.
The arithmetic since is the point of the whole story. In the 2024-25 season, the last for which a full count has been published, 41 pairs bred in the Nonsuch colonies and fledged 23 chicks, against 78 chicks island wide from a population of about 165 breeding pairs. Jean-Pierre Rouja of the Nonsuch Expeditions put the Nonsuch colonies at the second largest concentration of the species in Bermuda and therefore in the world, with 185 chicks fledged there in sixteen years.
The reason for all of it sits in the weather. The original islets are low, and a hurricane sweeping over them floods the burrows with the birds inside. Gonzalo drowned four or five males in 2014 and the females that came back to empty burrows abandoned them. When Melissa passed as a category two in late October 2025 the damage assessment found one nest lid washed off Green Island and little else, which was luck rather than safety.
Since 2013 a camera has run inside one of the Nonsuch burrows through the breeding season, which has done more for the bird's public standing than seventy years of fieldwork. A cahow can live around fifty years, and Madeiros, asked about the birds he handles now, told Canadian Geographic: “The birds I'm working with now, it's likely that they're going to outlive me.”
Almost nobody gets to see any of this, and that is deliberate. Nonsuch is closed to the public, full stop. Landing on it without permission is an offence and boats may not tie up at its dock. No tours run at all in January or February, when the birds are incubating, or in July and August, when there is not a cahow on the island: they are at sea from about mid June to late October.
The Bermuda Zoological Society has run occasional guided landings in the shoulder seasons, leaving from the dock at the aquarium in Flatts aboard the RV Endurance. They are not on a published schedule and the trip is not currently listed among the Society's standing programmes, so the way in is to ask the Department of Environment and Natural Resources directly, at terrestrialconservation@gov.bm. Arrivals disinfect their shoes in bleach before walking up the stair cut into the limestone cliff.
What is open, and what most visitors should do instead, is Cooper's Island on the south eastern tip of St David's. The Americans kept it after the 1995 base closure because NASA tracked spacecraft from it, handed it back in 2001, and it was protected as a nature reserve in 2008. There is a boardwalk, four beaches, and an observation tower opened in 2013 on the base of the old radar mount.
Boats may anchor off the north side of Nonsuch to snorkel the reefs there, though not to fish and not to land. That, the boardwalk at Cooper's Island and a camera pointed into a burrow are the whole of the public's access to the rarest seabird in the North Atlantic.