Fencing off danger

Predators don’t always come in large sizes. When it comes to hunting, cats and rats can hold their own. Christopher Pala visits a Hawaiian nature reserve, where a predator-proof fence keep these hunters away, allowing birds to live care-free.

Before Polynesian settlers arrived hundreds of years ago in their outrigger canoes, Hawaii had more than 120 species of birds – and no mammals to eat them. Land birds flourished in the absence of land predators, and seabirds flew in from all over the world to nest undisturbed on the ground.

All of that changed with the arrival of humans – and the dogs, cats, rats and mongooses that came with them. Hawaii became the extinction capital of the world; all but a few species of land birds disappeared or diminished to tiny numbers, and many seabirds avoided extinction only by flying to other islands.

But on Kaena, a wild, windswept point just 30 miles from Waikiki’s crowded beaches, the first predator-proof fence in the United States, built last year by Xcluder, a New Zealand company, is helping to restore the land to a pristine state and proving a boon for scientists and bird-watchers.

Fine mesh fence

The fine-mesh green fence zigzags about four-tenths of a mile, from the south coast to the north on Oahu’s westernmost spit of land. It is fitted with an overhang that lets rats climb out but not in. People enter through a two-door chamber, in which one door won’t open unless the other is closed. What has resulted is a slow-motion explosion of life.

“The fence is doing its job,” said Eric VanderWerf, a biologist who, with his wife, Lindsay C Young, is studying populations of albatrosses and shearwaters on a grant from the Packard Foundation. “The cats and mongooses were killing 15 percent of the chicks every year, and now they’re all gone.” Each week, VanderWerf drives from Honolulu to check a system of 1,100 traps, cameras and poisoned-bait stations for any indication that a predator may have sneaked in.

“The rats used to eat the seed of this plant, and now we’re seeing them sprout everywhere,” he said, pointing to a rare native ohai bush with exquisitely chiselled red flowers.

Nearly all of the 400 or so Laysan albatrosses that spend the nesting season here have been fitted with leg rings and have had their DNA taken, and many have been given GPS tracking devices, said Sheila Conant, a professor of zoology at the University of Hawaii.

“There will soon be a unique record of the individual history of hundreds of birds – where they went, who their mates are, who their offspring are and so on,” Conant said, adding that this kind of accessibility to data had led to the discovery a few years ago that nearly one-third of the nesting pairs are made up of two females, the biggest proportion of any known bird colony.

Kaena Point, a nature reserve, was a favourite haunt of off-road enthusiasts until 1990, when boulders were placed at the entrance to bar vehicles and protect native plants. Laysan albatrosses and wedge-tailed shearwaters soon began nesting there, the albatrosses on the surface, the shearwaters in burrows.

On a recent afternoon, VanderWerf walked across the point’s sandy soil, studded with white Laysans, the most common of the three Northern Hemisphere albatrosses.

According to the first count since the fence was put up, he said, there are about 400 birds here this season: 62 nesting pairs, 38 chicks and maybe 200 others, mostly juveniles who come to court or just to hang out. Some rested, their heads swung around and beaks tucked between folded wings; others waddled ungracefully. Pairs engaged in elaborate mating rituals involving a cowlike moo.

Meanwhile, the chicks, covered in chocolate-brown down, favoured the shelter of low-growing naio bushes, while their parents, who can travel thousands of miles while hardly moving their wings, roamed the northern Pacific for squid and small fish that they pick off the surface and later regurgitate into their chicks’ open beaks. All around were thousands of burrows dug by the shearwaters, whose mating season comes later in the year.

Rising population

“Since we’ve had the fence,” said Young, who studied the Laysans of Kaena Point for her doctorate at the University of Hawaii, “the number of albatrosses that come here has risen by 25 percent, and I expect it to continue.”

A glimpse of the future can be found at the world’s largest albatross colony, on Midway Atoll, 1,200 miles away in the Northwestern Hawaiian Islands, where about 1.5 million Laysans roost each year. They are so numerous, and such poor fliers at close quarters, that in nesting season bird counters are regularly knocked off their bicycles by low-flying birds. This correspondent, standing atop a low hill, was knocked down when a Laysan flew into his forehead.

A Midway albatross, named Wisdom, was ringed 60 years ago and is the oldest documented wild bird. She was spotted feeding a new chick this year.

On Midway, the density reaches 1,000 birds per acre, and about half of the 64 acres on Kaena Point offer terrain suitable for Laysans, so having “30,000 Laysans nesting at Kaena Point wouldn’t be unreasonable, and certainly 1,000 within 10 years,” Young said.

As VanderWerf surveyed a group of eight Laysans with his field glasses, he noticed that one was not ringed. So he simply walked over. The ringed ones took off, but the unringed bird just stared at the biologist, who caught him with ease. “It’s obvious he’s never been caught,” VanderWerf said as his assistant, Mike Lohr, carefully placed a ring on each foot.

Fewer crowds

VanderWerf said that Kaena Point offered advantages over Midway. Birds fight less because it’s less crowded. Fewer die from ingesting floating trash, because Oahu is farther from the denser parts of the Great Pacific garbage patch.

And Kaena Point’s elevation is greater – a haven from rising sea levels. (Last year’s tsunami killed a third of the chicks on Midway.) And from a scientific point of view, it’s easier to keep track of a smaller population.

For bird lovers, it represents the only place in the world where albatrosses can be observed at close quarters without supervision, fee or guide. Today, an estimated 50,000 people visit the point; they are asked to not bring dogs and to stick to roped-off paths.

“Most seabirds are in decline, and introduced predators play a big role,” said Conant, of the University of Hawaii. The fence, which cost $290,000, “is an affordable way to save them.”