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Cahow Knowhow

Class of 2002 return to breed

Four Cahows (Bermuda Petrels) ringed as fledglings during May 2002, returned to the nesting islets off Bermuda in February 2006.

Believed extinct for almost 300 years, numbers of Bermuda Petrels Pterodroma cahow have been slowly recovering since the species was rediscovered in 1951. Over the last five years, an ambitous 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 6m from the burrow it fledged from, but surprisingly also brooding an egg," explained Jeremy Madeiros of Bermuda’s Department of Conservation Services. "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 440m 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 seventy-five."
Added Jeremy Madeiros, Bermudan Department of Conservation Services 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.

Jeremy 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 occured 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 22 February."

4th July 2014