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Hurricanes highlight the need to protect cahow nest sites

A cahow and its day-old chick on CahowCam (Photograph provided by Nonsuch Expeditions)

This year’s hurricane season underlined the need to protect Bermuda’s national bird, researchers have said.

Jeremy Madeiros, the chief terrestrial conservation officer at the Department of Environment and Natural Resources, said in the winter edition of the Envirotalk Newsletter that Bermuda’s cahow population enjoyed another record-breaking breeding season.

But he added that hurricanes Teddy and Paulette hammered some of the small islands where the cahows breed and destroyed many of their burrows.

Mr Madeiros said: “Two of the original nesting islets were completely submerged by the 21 to 28 foot waves of these storms.

“Many of the artificial concrete nest burrows were damaged, with concrete nest lids washed overboard, burrows filled with debris, and quarter-ton boulders rolled across the nesting colonies, damaging burrows and requiring lengthy repairs.

You can access the cahowcam here.

“By contrast, the Nonsuch colonies, with burrows constructed at higher elevations than is possible on the smaller islets, were completely unaffected by the storms.”

This year saw a record 134 breeding pairs of cahow, which produced 69 chicks that fledged out to sea – just short of the 2019 record of 73 chicks.

Mr Madeiros said despite protections, researchers have discovered that long-banned pesticide DDT still hampered the species’ recovery.

He said blood and feather samples were collected from almost 90 cahows and tests confirmed the presence of DDT and DDE – its breakdown component – in most of the birds despite a ban on the chemical in the 1970s.

Mr Madeiros added: “Although the contamination is not in as high amounts as during the 1960s and early 1970s when it contributed to breeding success rates as low as 27 to 28 per cent, it is still present in high enough concentrations that it may be causing a reduction in breeding success.

“It may well be the reason why a relatively high percentage of eggs fail during incubation, keeping breeding success no higher than 53 per cent to 60 per cent, despite intensive management.

“By comparison, my other main study and management species on Bermuda, the longtail, has breeding success rates ranging from 68 per cent to nearly 80 per cent at the study locations.”

Mr Madeiros said research into the movements of cahows in the Atlantic have continued with tiny GPS tags used to collect information.

He added: “These tags are accurate to within a metre or two, enabling tracking the movement of the birds very precisely, and even to determine the speed of the birds flying between their nests in Bermuda and the distant foraging areas.

“The information gained revealed that cahows regularly carry out feeding trips to gather food for the growing chicks spanning thousands of miles, to the edge of the Canadian Continental Shelf, and beyond to the Grand Banks.”

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 and new two colonies were established on Nonsuch Island through relocation.

The species later set up home on Southampton Island on their own.

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Published December 18, 2020 at 9:13 am (Updated December 18, 2020 at 9:19 am)

Hurricanes highlight the need to protect cahow nest sites

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