Work to establish thriving cahow colonies on Nonsuch Island continued to pay off in 2022 with the island now home to the second-largest population of the critically endangered birds.

Jeremy Madeiros, the Department of Environment and Natural Resource’s principal scientist for terrestrial conservation, said in a recent report that almost half of chicks translocated to Nonsuch Island as part of the project had returned to the site.

“These nesting colonies have rapidly grown by 2022 to become the second-largest subpopulation of all the nesting islands at 35 breeding pairs, and continue to grow and attract even non-translocated cahows from the original islands,” he said.

“This is largely because the new colonies are located at a much higher elevation on Nonsuch than on any of the other islands and have not been disrupted or damaged by hurricane waves, storm surge and erosion.”

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Cahows – also known as Bermuda Petrel – were believed to have been wiped out by the 1620s, but the species was rediscovered in 1951.

While the population at that time was limited to only 18 breeding pairs, which produced seven or eight chicks a year, efforts to revive the species have resulted in the population bouncing back.

Mr Madeiros said the 2022 season had resulted in a record-breaking 156 breeding pairs and 77 chicks fledged.

Early indicators suggest that the 2023 season could surpass that with a “near record” number of sightings when the birds returned to the island in the fall for their courtship period.

“The first returning adult cahows were recorded on Green Island by December 30 and we are now waiting for the imminent return of the rest of the population in early January 2023 to lay their single eggs and begin the 53-day incubation period,” Mr Madeiros said.

“Although it is still too early to know the exact number of confirmed breeding pairs until all birds have returned to lay their eggs – only pairs that produce an egg, whether it hatches or not, are counted as actively breeding pairs – it looks like 2022’s record of 156 breeding pairs will be easily exceeded, with hopefully at least eight new pairs likely to come ‘online’ and produce their first eggs.

“One new development of note is that prospecting visits to the nesting colonies on Nonsuch by newly returned, young male cahows continued through much of November and the exodus period in December.

“This is highly unusual, as most prospecting by young adults looking for nest sites does not occur until February and March. It will be interesting to see whether this is a one-time event or is new behaviour related to the continuing increase in numbers of nesting cahows.”

Mr Madeiros said that Hurricane Fiona had damaged some of the smaller islands where cahows nest, with a number of man-made concrete nest burrows impacted or filled with debris.

However, the burrows were repaired in time for the arrival of the first cahows in mid-October.

Mr Madeiros added that over the course of 2022 researchers retrieved geolocator tags that had been fitted to the legs of several adult cahows one or two years earlier.

The tags were used to track the birds movements and identify their feeding areas, which include the Grand Banks east of Nova Scotia and cooler, more productive waters well north of the Gulf Stream.

Mr Madeiros said: “In May and June, 37 GLS tags were fitted for the first time to fledgelings just about to leave the nests, which will gather data for three years, archiving it until the tags can be recovered when the young birds return to nest.

“This will fill an important gap in knowledge, as nothing is presently known about where young cahows go during the years when they are exploring and learning to survive on the open ocean.”

Mr Madeiros said work has also been done to update the popular CahowCam infrared camera system on the island, which offers researchers and members of the public a glimpse inside the cahows underground nests.

“Despite the continuing recovery of the cahow, it is still critically endangered and one of the rarest seabirds on Earth,” Mr Madeiros said.

“Continued management to control both old and new emerging threats will be essential to enable the continued recovery of Bermuda’s beautiful national bird.”