Hurricanes could pose an increasing threat to Bermuda’s national bird as cahows have increasingly been returning to the island earlier in the year.

Jeremy Madeiros, a terrestrial conservation officer with the Department of Environment and Natural Resources, said in a video posted on the Nonsuch Expeditions website that in recent years a growing number of cahows were recorded earlier than expected.

“This seems to be a trend I have been recording, particularly over the last six or seven years now where more and more birds are coming back earlier and earlier every year,” he said.

“This sort of mirrors what is happening with the longtails or tropic birds here in Bermuda, and in fact a worldwide trend where species are adjusting their breeding cycles because the climate is changing, and changing rapidly at this point.

“In a way, it is not good because it means they are returning when hurricane season is still under way.”

He added that with the earlier arrival of the cahows, a late-season hurricane could spell disaster for those birds that nest on smaller islets, some of which are completely flooded by large storms.

“Here on Nonsuch these birds will be safe, thank goodness,” he said. “That is what I have really focused my management of the species on over the last 20 years, getting them onto a higher, safer nesting area where they are safe from sea-level rise and hurricanes for centuries to come.”

Mr Madeiros argued that people have an ethical obligation to help protect the species given the human role in the decimation of their population.

“We have changed the conditions under which they are expected to survive in,” he said. “Rather than make it more difficult for them to survive, if we can make it a little bit easier for them to survive, then we redress the imbalance that we caused ourselves.

“Nature has already been hugely affected by man.

“We are having a planet-wide detrimental impact on ecosystems everywhere and there are a million species that are in danger of going extinct in the next few decades.”

Cahows, also known as Bermuda petrels, were largely wiped out by introduced predators and hunting by early English colonists.

By the 1620s, the species was believed to be extinct.

However, the species was rediscovered in 1951, with a handful of the birds found nesting on four rarely visited rocky islets, which sparked efforts to rebuild the population.

As part of the project, man-made burrows were created on Nonsuch Island, with chicks translocated to the island in the hope that they would return to Nonsuch as adults.

The project has borne fruit, with a growing number of birds fledging on the island and, for the first time since the 1620s, a cahow couple last year successfully dug its own burrow and raised a chick inside it.

Mr Madeiros posted on the Nonsuch Expeditions blog that rough weather limited his ability to check on cahows during their courtship period this year. However, the birds he was able to examine were in healthy condition.

“So far this season, I have been able to confirm that almost all adults are in good body condition and at good weights,” he wrote.

“I have also been able to confirm at least four first-return birds, that is, young birds that have been out at sea for three to five years after fledging as chicks, and are now mature and returning for the first time, the males to choose new nest burrows and attract potential mates, and the females to choose mates with good nests.”

Mr Madeiros said the seabirds returned to the island in late October and remained through November for their courtship and nest-building phase of their nesting season.

After their courtship and nesting period, the cahows return to sea to “feed intensively” throughout December, with the females developing their single large eggs, and the males building up fat reserves to carry out most of the early egg incubation.

The cahows then return to their burrows to lay the egg and care for it in turns.

Mr Madeiros said the first cahows of the nesting season were found in their burrows on the “very early date” of October 14, and that he had surveyed them throughout the latter half of October and November, both on Nonsuch and on five smaller nesting islets and rocks.

“The combined area of all six nesting islands, including Nonsuch, totals only 22.2 acres, of which Nonsuch by far is the largest of these at 16.5 acres,” Mr Madeiros said.

“However, the weather conditions during much of November have been characterised by lengthy windy periods, making it too dangerous to travel out to and land on the nesting islands, except on just one or two days of each week, rather than the more usual three to four days.”

He wrote that he usually tried to process and measure at least 100 adult cahows during the courtship and nest-building period, but because of the weather he was only able to handle about 80 of the birds.

“After the birds return in the new year to lay their eggs in their underground burrows and begin egg incubation, I have an objective of processing at least another 100 cahows during the egg-incubation period of the nesting season in January and February,” Mr Madeiros said.

• For more information, visitwww.nonsuchisland.com