THE Bermuda Audubon Society is pleased to present a second article on Bermuda’s birds, as part of this year’s Caribbean Endemic Bird Festival, organised by the Society for the Conservation and Study of Caribbean Birds. Jeremy Madeiros the Terrestrial Conservation Officer with the Department of Conservation Services, offers an insight into the life of the Cahow. Jeremy has worked with the Cahow for over 20 years and has been in charge of the Cahow Recovery Programme since 2000.

THE Cahow or Bermuda Petrel (Pterodroma cahow) is Bermuda’s national bird and is a true endemic species, unique to the island and nesting nowhere else on earth. The Cahow is a beautiful, long-winged seabird of great historical significance to Bermuda’s early days of human discovery and colonization. Because of its rarity and the fact that it only flies into its nesting grounds at night, it has more than once been called the “ghost bird.”The Cahow belongs to a family of seabirds known as Gadfly Petrels, so called because of their powerful, fast and agile flight.

It is highly pelagic, meaning that it spends most of its life living and feeding on the open ocean, often hundreds of miles from land, which it only visits to nest. It has a body length of 15 in. (38 cm) and wingspan of 35-37 in. (89-94 cm).

The upper body, wings and tail are dark to medium-gray in color, sometimes tinged with brown, with a crescent-shaped white band across the rump. The underside of the body and wings are white with dark edges and tips and a distinctive dark spot or “thumbprint” on the underwing.

One characteristic feature of the Cahow is its strong, sharply hooked black beak which is used for catching small squid and fish as well as shrimp-like organisms.

Another feature is its relatively long legs (in comparison to the Longtail’s short, almost useless legs) and strong, webbed feet which it uses for swimming, climbing and digging out its nest burrows when enough soil is available.

To survive in the harsh ocean environment, the Cahow has special adaptations, including a highly efficient gliding flight which uses only 13 per cent of the energy used by other seabirds, which must regularly flap their wings to stay in the air.

They also have a special gland in the nostrils which enables them to survive at sea by drinking seawater. The gland excretes the excess salt in the form of drops of brine, which are “sneezed” from the unusual tube-like nostrils on top of the bill.

When Bermuda was discovered by Spanish and Portuguese explorers in the early 1500s, the Cahow was abundant, numbering possibly in excess of half a million pairs that nested in long burrows in sandy soils or in deep rock crevices.

Their strange nocturnal courtship calls (low moans followed by higher pitched cries) convinced the superstitious Spanish sailors that Bermuda was inhabited by devils, with the result that they never settled the islands. The Spanish did however release pigs or hogs to provide food for shipwrecked sailors. The pigs multiplied rapidly and decimated the Cahows on Bermuda’s larger islands, rooting up and eating eggs, chicks and adults in their burrows.

By the time of the English Sea Venture>shipwreck in 1609, Cahows were already confined to smaller offshore islands that the pigs could not reach, where they still nested in impressive numbers.

The first permanent English settlers arrived in 1612 and accidentally introduced rats, which ate all of the settlers’ food and crops, causing a famine. The Cahow was heavily predated on by the rats, as well as by cats and dogs introduced to control the rats, and by the desperate settlers, who ate the birds by the thousands.

By 1620, the Cahow population was decimated and the bird seemingly disappeared and was presumed extinct. But for over three centuries a tiny remnant population continued to breed, unknown and unseen, on some of the smallest, most inaccessible islets off the east end of Bermuda, safe from most mammal predators.

In 1951, following the discovery of at least two recently dead petrel specimens, a scientific expedition was mounted to see whether the Cahow had, against all odds, managed to survive on Bermuda’s rocky offshore islets.

And, to the delight of the scientists, a few nesting birds were discovered.

Participating in the expedition was 15-year old schoolboy David Wingate, who, after returning from college in 1958, became the Government Conservation Officer in charge of the Cahow Recovery Programme until his retirement in 2000.

Since intensive management of the Cahow began, its population has increased from 18 pairs producing eight fledged chicks in 1962 to 76 pairs with 36 chicks successfully fledged in 2006. So far in 2007, there are over 80 active nest sites, including five new nest burrows being prospected by new pairs, with what appears to be at least 38 chicks.Despite the continuing increase in the Cahow population it remains critically endangered and still nests on only a few tiny rocky islets totaling barely two acres in area.

The species faces its greatest threat from erosion and over-washing of the present low-lying nesting areas during hurricanes.

Other threats include predation by rats, which occasionally swim out to the islands from the Bermuda mainland. Rats are controlled as part of the management program by monitoring and the use of poison bait to keep the nesting and all adjacent islands rodent-free.

Nest site competition with the relatively common and aggressive Longtail is prevented with the use of wooden “baffler” plates which have specially shaped entrances that allow access by Cahows but prevent the larger-bodied Longtails from gaining entry, killing the Cahow chicks and taking over the burrows.

Because there is no soil on the present nesting rocks for the Cahow to dig its own nest burrows, there is an ongoing programme to construct artificial burrows out of concrete to enable the nesting population to increase. These have been readily used by the birds to the point where they are used by almost 80 per cent of the nesting pairs.

To counter the continuing threat of damage and possible destruction of the tiny present nesting rocks by hurricane waves and rising sea levels, a program was started in 2004 to establish a new Cahow nesting colony on the much larger and higher Nonsuch Island.

This island is managed to control predators and human access and has enough suitable habitat to enable the Cahow to eventually build up a much larger population than is possible on the present sites. Because the Cahow chicks tend to return to the area they originally fledge from, and then look for new nest sites close to already active nests, the programme is using two techniques to establish the new colony. One is the translocation — or moving of chicks — about three weeks before they fledge from the present nesting islets to a new group of artificial nest burrows on Nonsuch.

Once settled in their new homes, they are fed and their growth monitored daily until they are fully mature.

They then naturally come out of their nest burrows over several nights to exercise their flight muscles and imprint on their surroundings before they depart to sea on their own, not returning for several years.

Fifty-five chicks have already successfully fledged from Nonsuch Island, with the first returns expected over the next couple of years. The other technique is the use of a solar-powered Sound Attraction System at the new colony site, which plays back recordings of Cahow courtship calls. This is to trick any returning birds that the site already has active nests occupied by breeding birds, so that they can land and occupy the artificial nests built at this location.

The Cahow is a tough and remarkable survivor which has already defied the odds and is continuing a slow but accelerating recovery despite continuing threats.

This is entirely due to a long term, intensive management program which is being used as a model for the management of other endangered seabirds world-wide. It has become a well-known symbol of hope for conservation efforts internationally, and is both a very special part of Bermuda’s natural heritage and very worthy of its title as the island’s national bird.