Conservationists who discovered four dead cahows on Nonsuch Island are investigating what may have attacked them.

Jean-Pierre Rouja, the founder of Nonsuch Expeditions, said the birds were likely killed by either an owl or raptor such as a falcon at the St George’s nature spot.

The cahow, Bermuda’s national bird, is subject to extensive conservation efforts as their numbers are low and the species is qualified as endangered.

There are colonies on Nonsuch and surrounding islands. Jeremy Madeiros, the terrestrial officer for the Department of Environment and Natural Resources, manages the nesting sites, carrying on the work of conservationist David Wingate.

Mr Rouja said: “Cahows are nocturnal and will only approach land after sunset, conducting all of their aerial courtship and activities outside of their underground burrows after dark.

“This behaviour likely evolved as a way to avoid daytime-hunting eagles, hawks and falcons.

“However as was documented by at least two similar kills 15 years ago, also on Nonsuch, peregrine falcons have been known to hunt them under the light of a full moon. They are well documented as being able to hunt the related and similar-sized Manx shearwater, during full moon periods on islands off the coast of Wales.

“There had been a super full moon earlier in the month and the state of the carcasses was such that these kills could have happened around that time. A peregrine falcon had been seen roosting on Nonsuch around the time as well.

“Historically, when they are blown in to Bermuda, they will stay for a week or two until they build up their energy and fat reserves, and then resume their migration heading south to the Caribbean and South America, which would in these circumstances be the best-case scenario, as this might limit the killings to the few we had found already.”

Mr Rouja highlighted that in 2012, Mr Madeiros and his assistant were positioned just off Nonsuch when they saw a short-eared owl flying from the sanctuary over to Green Island, where it appeared to be hunting.

This instantly makes the owl a suspect as well, Mr Rouja said.

“Short-eared owls are on the smaller side and likely couldn’t catch a cahow in flight, although could conceivably attack a younger prospecting one, exposed on the ground at night,” Mr Rouja said.

However, having taken all the facts into account, Mr Madeiros believes that the perpetrator was most likely a peregrine falcon, which seems to have moved on after feasting on the birds.

Mr Rouja added: “Hopefully that is the end of this matter, at least for this season.

“The Department of Environment and Natural Resources, Nonsuch Expeditions and project partner BioQuest will now attempt to extract DNA from the carcasses, which once compared with birds from their ongoing Cahow Genomic Population Study, should be able to determine if the victims were young prospecting cahows or older ones, perhaps part of established pairs, which would be far more disruptive to the ongoing recovery programme.”

For more information about the incident, visit www.nonsuchisland.com.