FOUR cahows (Bermuda petrels) ringed as fledglings during May 2002 returned to the nesting islets off Bermuda in February, according to the conservationist web site BirdLife International.

Believed extinct for almost 300 years, numbers of the Bermuda cahow have been slowly recovering since the species was rediscovered in 1951.

Over the last five years, an ambitious recovery programme involving relocation and construction of artificial burrows on "hurricane-proof" islets has helped raise numbers to around 250.

Two of this February's "first-return" birds were recovered in nest burrows.

"One was in a burrow located very close to the burrow it fledged from and, surprisingly, was also brooding an egg," Government Conservation Officer Jeremy Madeiros explained.

"As this was an established nest with both adults banded two years ago, this new bird either has displaced one of the previous adults, or has replaced one after it suffered mortality."

The other chick was found in a nest already claimed by an established pair, which had failed to lay an egg this year and left the nest relatively early in the season.

"The bird was therefore probably prospecting for a new nest and stayed over for the day in this one. But what was really surprising was that this particular bird originally fledged from another nesting islet 440 metres away from the one where it ended up.

"Another nine nest burrows are also being prospected this year, with pairs of adults now being confirmed in three of them. Although it is still a bit too early for a final estimate, the total number of active established nest sites this year appears to be about 75," Mr. Madeiros said.

The second pair of first-return birds were captured at night on the same islet, when they landed among an existing complex of active nest burrows. One of these had fledged on the islet; the other had come from the islet 440 metres away.

Mr. Madeiros thinks it most likely that the two birds not originating from the islet were attracted by the greater amount of activity, as it has by far the largest number of breeding pairs of cahow (30 pairs).

He says there has also been a unusually large amount of new nest-prospecting activity.

"In 2005, prospecting occurred at a total of eight new nest burrows, with pairs of adults being confirmed at five of them. All five of these new pairs have produced eggs in 2006, with only one failed egg as of February 22."

Bermuda's national bird has been the subject of two acclaimed documentaries in recent months ? by the Irish film-maker ?amon de Buitl?ar and local writer / director Lucinda Spurling's , which premiered last week at the Bermuda International Film Festival.