Our unbelievable Cahow

  • Petrel expert Nicholas Carlile of the Department of Environment and Climate Change in New South Wales in Australia and Bermuda Conservation Officer Jeremy Madeiros with a cahow on Nonsuch Island.

    Petrel expert Nicholas Carlile of the Department of Environment and Climate Change in New South Wales in Australia and Bermuda Conservation Officer Jeremy Madeiros with a cahow on Nonsuch Island.
    (Photos by Chris Burville)

  • A cahow is banded to track its movements at sea. The bird has been found to range as far north as the Canadian Maritime provinces and Ireland and as far south as the Canary Islands off North Africa.

    A cahow is banded to track its movements at sea. The bird has been found to range as far north as the Canadian Maritime provinces and Ireland and as far south as the Canary Islands off North Africa.

This year, a likely reason for the survival success of the cahow has been discovered by the work of the Conservation Officer and his team.

He said: “The cahows have this extraordinary ability we have tracked them travelling 4,500 miles to feed their chicks once; they have gone to Nova Scotia, Newfoundland and the mid-Atlantic ridge. We are finding that the cahow can go thousands of miles to find food.

“They are foraging all the way up to the edge of the pack ice in the St. Lawrence. That’s why we think the food for the chicks when they first hatch is krill, from places with very cold water temperatures.

“It is a speciality for them, right after they hatch, and then they switch to squid and fish.”

He explained the parent birds entirely act on instinct to seek out the krill, and so follow the winds to these northern latitudes.

He explained that while they were aware that cahows do fly hundreds of miles to their feeding grounds and don’t spend much time in Bermuda, until the last year there was very little knowledge about their movements.

“We knew they feed off the Carolinas, 600 miles away at the closest point, and otherwise, 200 miles east of Cape Cod, and in Canadian waters.”

He noted: “It is the Holy Grail the pinnacle for bird watchers in that area to see a cahow, because it has been spotted on average just once every three years.”

But the conservation team have now discovered the cahows are going much further than that. “These birds are using storms to sling-shot them on their way that wind is raw, free energy.

“We have been able to confirm that they will catch a free ride on a south-westerly wind, ahead of the storm, which will shoot them north-easterly out and up into the Atlantic,” said Mr. Maderios.

“In some cases, we have recorded them travelling 450 miles in a day at this rate they could cross to the US in a day and a half!

“The secret is, they catch a ride on these storms’ free wind to their feeding grounds, near the Azores or the Grand Banks, to forage while the storm passes.

“Then, behind the storm, there are north-easterly strong gale force winds, so they hitch a ride on those winds straight back to Bermuda!”

The first indications that the cahows were travelling these great distances first were discovered two years ago.

It was in January 2009 that petrel expert Nicholas Carlile of the Department of Environment and Climate Change in New South Wales in Australia came to Bermuda to help set up the data logger aspect of the cahow project, affixing tiny location detection devices to the birds and then downloading the information when the loggers were retrieved.

“The Australians couldn’t believe the distances it’s the same kind of distances the albatrosses are doing and these birds are a quarter of the size.”

The distances were so great that the conservation officer felt it was important to double check the results.

“We were suspicious when we got the first tags back, so we put the word out to Canadian fishermen and others in the northern regions where the cahows were being logged.”

They duly received reports that they were occasionally being seen in those areas.

“We thought the bird might have been confused with other petrels. But when we got a photograph, it was unmistakeably a cahow. So we know, every year, they go up to Canadian waters.”

He said: “We’ve now been able to follow nine birds for a year or more one for two years.

“We have found, from those nine birds, that the minimum distance in 12 months is 36,000 miles; that is, taking the fixed recorded points in a straight line.

“The champion went 81,000 miles the equivalent of four times around the equator. It is an unbelievable distance. They can go anywhere they want. We’ve had a couple go fairly close to the Canary Islands.

“Of the nine, two thirds of them spend the summer near the Azores. That was a surprise, that there was this Azorean connection.

“We think they go to that part of the Atlantic because that’s where shrimp spawn. In fact, sperm and beaked whales also go there to feed.

“But, a third of the birds stayed between Bermuda, Nova Scotia and North Carolina. They spent the whole year in that area.

“Some birds may spend the summer in different areas. Some seem to prefer to go further distances, while others like to stay closer to home. So it seems to be a personal preference.

Summarising their findings, he said: “We’ve discovered an increase in their range by 20-fold, to a million or so square miles.

“We now know they forage along the coast of Western Europe, across the entire North Atlantic 4,000-5,000 miles. We are still catching our breath over this.

“We have recorded one bird that went almost as far as Ireland, and then to Spain and Portugal and France we’ve now got birders who want to go out and look for them from Ireland. They can exploit food resources across the entire Atlantic.”

“We are now using smaller tags to see if the same birds go to the same places or not. We’ve raised a lot of new questions.

The cahow is a creature of the north Atlantic a true Bermudian, because he loves to travel to exotic places.

The cahow’s ability to survive while at sea is greatly enhanced by the fact that they are able to travel such enormous distances.

It means that if a food source is not available in one region of the Atlantic: “… they can move somewhere else,” said Mr. Maderios. “It bodes well for their survival it is not like they’re stuck within a couple of hundred miles.”

Although the results gathered from the data loggers have been remarkable, these birds are in fact constructed perfectly for this sort of extreme flight.

“The design of the bird the wings compared to body size are the longest wings of any sort of bird species, so the wing load is very light, meaning they use a minimum of effort to stay in the air. They use only nine to 13 percent of the energy of a gull, for example,” he said.

“Over the open water, they glide at high speed, and very low then dive into the trough of a wave where there is no wind, and then pull up and over the crest of the wave.

“They are hit in the face by the wind, so they gain height, but lose speed. Then, they dive into the trough of the wave again, gain speed and lose height they do this ballet for hundreds of miles.

“They are like the albatross in the southern oceans; but while they are like the fighter jets of the sea bird world, the albatross is the B52 bomber.

“Cahows definitely have the best design for going fast over long distances with the minimum expenditure of energy.”

Australian petrel expert Nicholas Carlile, who brought his expertise to the cahow relocation project in the aftermath of Hurricane Fabian in 2003, came back in Bermuda two years ago, bringing with him the tools to help answer the question of where the cahow goes during its many months at sea.

Mr. Carlile has been involved in seabird and island research for more than 20 years with the Department of Environment and Climate Change in New South Wales in Australia.

During his three week visit here he and Conservation Officer Jeremy Madeiros fixed pea-sized data loggers to 12 cahows.

This tiny and sophisticated piece of equipment collects location information and stores it while the bird is at sea.

Upon the bird’s return the logger is removed from the bird, and the information stored on them is downloaded to tell scientists in general terms where and on what routes the birds travel when they leave their burrows.

Nonsuch Island in Castle Harbour, which has been returned to its endemic origins, has taken a further big step back to those roots.

The cahow has officially established a colony there with a new chick, called Bermudiana, having been successfully raised by its parents from egg to fledgling.

Bermudiana was named after one of the babies that were born here while the Sea Venture passengers and crew were stranded on the Island’s shores and a very few years before the very last cahow chick fledged from Nonsuch.

The first chick, born to the same parents as Bermudiana, required some assistance from Mr. Maderios in order to successfully fledge, had been called Somers, after the flag ship Sea Venture’s Admiral Sir George Somers. “So we have a Sea Venture theme,” he noted.

“We had three pairs that did lay eggs but they did not hatch, which is very common because these first-time parents are inexperienced. So truly, 100 percent, Bermudiana was the first.

The year, the new breeding season has already started. “We are going from strength to strength,” said Mr. Maderios. “We’ve got eight pairs established in nest burrows and another five nests which are being prospected by young male cahows, who then spend the next year or two attracting a mate.

“So, we’ve got 13 burrows with cahows in them. Already, we have more than enough.

“Of the chicks we have translocated to Nonsuch over the last decade or so, 102 chicks fledged out to sea, and we have had a 20 percent success rate already with 12 of 21 returns, which is a 60 percent survival rate.

“We are also preparing the ‘b’ nesting site on Nonsuch Island so the cahows will have two foot-holds there. The two sites should eventually merge and make one colony.

“I’ve always believed you don’t put all your eggs in one basket. We had a lightening strike in 2006, which killed a casurina tree. The shock could have affected any chicks in the burrows. It’s better to have a second site it’s insurance, basically,” he explained.

Another reminder of the wisdom of this philosophy was Bermuda’s recent brush with Hurricane Igor.

“That hurricane didn’t cause any thing like the damage that Fabian caused. However, one of the nesting islands has become two islands, and all the islands lost big chunks.

“It reinstilled the need to relocate them from these vulnerable spots. It was another wake up call.

“Certainly, climate change is affecting the integrity of the structures, and that’s the real fear a couple of those islands may not be here any more after another bad storm.

“At least now there is an alternate place that’s safe from this sort of erosion for thousands of years.”

“The programme is important to educate the Bermuda public about it is our natural heritage.

“It is hugely important internationally we are held up internationally for our environmental initiatives the turtles, the tropic birds and our coral reef protection.

“We are held up as an example of what should be done.”

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Published Mar 10, 2011 at 8:28 am (Updated Mar 10, 2011 at 8:27 am)

Our unbelievable Cahow

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