Seventy years after its rediscovery, the Cahow continues to surprise conservationists as the seabirds reclaim old territory on Nonsuch Island.

Jeremy Madeiros, Bermuda’s senior terrestrial conservation officer, got an unexpected treat yesterday visiting the remote reserve.

Spotting fresh soil dug from an artificial burrow, Mr Madeiros lifted the lid on a new nesting pair.

He said: “That’s just phenomenal – they are exploding on this island now. I’ve never had birds in this nest before.”

The new nest, numbered R827, yielded a female without a leg band, meaning she was from one of the few natural burrows.

Mr Madeiros handed over the male, which had a numbered band, for a reporter from The Royal Gazette to hold while he checked the female’s weight.

The birds looked impatient to get back underground.

In a month or so, the single eggs guarded by at least 142 nesting pairs will start hatching in what Mr Madeiros and fellow Cahow custodian Jean-Pierre Rouja hope will be another record year for one of the world’s rarest seabirds.

Vanished for centuries and discovered on January 28, 1951 clinging to a handful of rocky islets off Castle Harbour, the Cahows’ comeback on Nonsuch is now critical to its long-term survival.

Mr Madeiros pointed to extensive shoreline damage from the latest hurricanes.

Giant swells from Hurricane Teddy last year were more than enough to submerge the smaller islets where Cahows have nested for the last seven decades.

A landmark offshore crag was halved by Hurricane Fabian in 2003, and Mr Madeiros said other islets were “melting like sugar cubes”.

But on the 14 acres of Nonsuch, high above the sea, Cahows were reintroduced in 2004 for the first time in centuries.

This is the first year a pair dug its own burrow in the sandy soil of the island, which was returned to its natural state by Mr Madeiros’ predecessor, David Wingate.

Dr Wingate retired in 2000.

Mr Madeiros never knew the birds could be handled until 2001, when he met Australian scientists reviving similar lost populations of seabirds.

He said: “We didn’t know much about them, so there was a no handling policy. David didn’t want to do anything that might have a detrimental effect.

“What we didn’t know was scientists in Australia and New Zealand had been doing it for decades.”

Handling Cahows with the right touch enabled better study, as well as translocating chicks to Nonsuch – and feeding the young to top health.

Mr Madeiros said the birds got “a lot of anchovies and fresh, unfrozen squid, all so expensive I wouldn’t eat it for myself”.

Hand-fed birds would imprint on Nonsuch, then fly out for a few years at sea, mapping thousands of miles of ocean into their brains before heading back.

Cahows were famous from Bermuda’s earliest history for their strange calls.

Yips came from some of the burrows as the birds sensed visitors.

Mr Rouja showed images from one of his CahowCams, able to watch the pair in the dark underground.

He said: “You can see they’re listening to us. Let’s look at CahowCam 2.”

The pair under the first camera were vying for space to sit on their one egg, while Cam 2 showed a lone male incubating.

The cameras come from a private venture, Nonsuch Expeditions, which Mr Rouja leads. It now has about 40 million minutes of video.

Another camera looks out to sea, and can show the birds taking to the night skies.

The young need cold water food, and parents will fly hundreds of miles to catch and bring it back.

Cahows emerge only on dark windy nights, and will remain at sea until moonless conditions allow them to approach land.

Mr Madeiros explained that tonight’s storm, which will blot the full moon and buffet Nonsuch, would bring out Cahows seeking mates and flitting over their island.

He said the sound was “hard to describe – it’s completely unearthly”.

“It’s a low moan, almost mooing, followed by high-pitched yips, and cries that just ring out.”

Mr Rouja said it was easy to believe the early accounts of sailors who called Bermuda the Isle of Devils.

He added: “In the pitch dark, it would have been completely freaky.

“You wouldn’t know where the sounds were coming from. They move so fast. And in the old days there would have been hundreds of thousands of them, maybe millions.”

With new threats such as climate change, conservationists think in long terms about Cahow restoration.

As Mr Madeiros returned a Cahow to its burrow, he said: “We know now these birds can live 50 to 60 years. This bird may well outlive me.

“When I took this over, we had about 56 nesting pairs. When they were rediscovered in 1951, 17 or 18 was the entire world population. Nobody knew this secretive family of seabirds on remote islands – I’ve had the job of figuring it out.”

Mr Madeiros confirmed he was looking for successors, although he declined to name names.

He said he did not expect Cahows to fully reclaim Nonsuch under his watch.

But he added: “These last five years we’ve really seen the fruits of the labour.

“This colony is fully established. It’s been decades to achieve. But it’s been really worth it.”