Cahow nesting season “kicked into high gear” this week.

Experts said another record-breaking year for the critically endangered birds was expected.

Jeremy Madeiros, terrestrial conservation officer with the Department of Environment and Natural Resources, said the seabirds appeared to be in good health as they returned to Bermuda this week to lay their eggs.

Mr Madeiros said: “In nest checks that I carried out on January 5 and January 8, it was determined that more than half of the cahows in the breeding population have now returned to their nest burrows on several of the Castle Harbour islands – the only location on Earth where the cahow breeds.

“Measurements carried out on the returned birds show that for the second year in a row, the birds are at very healthy, near-record weights for the beginning of egg incubation, with some males recorded at over 500 grams.

“This indicates that they have been able to find plenty of food items during the last month at sea, which is a good sign for the chicks when they hatch in early to mid-March.”

Mr Madeiros said early indicators suggest the total number of nesting pairs could top 140 this year – which would beat the record of134 set last year.

He added: “This is still a tiny overall population, with the cahow remaining one of the rarest seabird species on the planet, being listed as critically endangered."

The cahow, or Bermuda petrel, was believed to have been wiped out after British settlement in the 1600s.

But the species was rediscovered in 1951 after 17 to 18 nesting pairs were found in burrows on rocky islets in Castle Harbour.

A major conservation effort was launched to bring the species back from the brink of extinction.

Jean-Pierre Rouja, Nonsuch Expeditions founder and team leader, said CahowCam 1 – a hidden camera inside a burrow on Nonsuch Island – live streamed the laying of one cahow egg around the world on Saturday night.

He said: “As our followers from around the world watched live, the male from the underground CahowCam 1 burrow returned at 6.25pm.

“Amazingly, despite having been apart at sea for more than two months, he was able to coordinate with his mate which arrived less than four hours later at 10.20pm.

“As Jeremy had predicted the day before, she then laid her single egg within the hour, revealing it partially to our online viewers by 11.24pm.”

The female left the nest just before 3.30am and left the male to incubate the egg while she recuperated at sea.

Mr Rouja said: “If all goes well the egg should hatch around the beginning of March, followed by three months of feeding trips, which can cover hundreds to thousands of miles as the parents seek out cold water fish, shrimp and squid north of the Gulf Stream.”

The burrow will continued to be live streamed at www.nonsuchisland.com as part of the ninth season of LookBermuda’s Nonsuch Expeditions CahowCam project, created in partnership with the Cornell Lab or Ornithology.