KRARRAH, kwink, kwink, kwink" - A bird with a long blue tail and blue wings swoops down from a camphor tree, hops on the grass, picks up a tasty bug morsel and dashes back to its bough.

It's an azure-winged magpie (cyanopica cyana), offspring of those introduced to the Bird Island in Pudong's Century Park seven years ago as potential insect killers.

After some ups and downs, deaths and escapes, the avian pest-control experiment worked. It's now a permanent part of the efforts to maintain an eco-friendly park and cut down on use of biopesticides.

Today about 500 azure-winged magpies consider Century Park their home and feeding ground.

With their help, pesticide usage has steadily declined in the park. Last year, the park used about 400 fewer kilograms of biopesticide than in 2007, and that was 200 kilograms fewer than in 2006.

This is believed the only city case of intentionally using magpies to control pests, though magpies can be found around the city.

Magpies, members of the crow family, are traditionally considered birds of good luck in China.

They have glossy black heads and white throats and these have the beautiful azure wing and tail feathers.

These are 33-35 centimeters from beak to tail and they're more slender than the European magpie (pica pica).

In 2002, the park introduced the first 118 nestlings to Bird Island. At first they depended on humans to provide food, responding to a whistle at meal time, but they gradually learned to catch insects by themselves.

Most of the birds now are second- and third-generation, never eating from human feeders and considered wild.

"Though it took a lot of time and effort to introduce, raise and keep the magpies in the park at first, it was worth all the effort," says Sun Jiayi, director of the Business Management Department of Shanghai Century Park Management Co.

"This proves it's possible to replace pesticides with biological methods, like using natural bird predators," he says.

It's far cry from the days of the "Kill a Sparrow Campaign," or the "Four Pests Campaign" in the "great leap forward" (1958-1962). Magpies were killed along with other birds and the four pests (sparrows, rats, mosquitoes and flies) in the belief that they were eating grain and reducing harvests.

Once magpies, with their distinctive calls, were found throughout leafy Shanghai, then they disappeared with urbanization. But they're back.

They are omnivores, eating all kinds of invertebrates, larva, fruit, berries, acorns, nuts and, of course, human scraps. Insects like the nasty pine moth, other moths, flying beetles and cutworms are their favorites.

A single pine moth usually eats about 30 pine needles every day. A 10-year-old pine can be eaten bare by 100 pine moths in 15 days.

Their poison bristles protect them from many birds and they are resistant to many pesticides.

But the magpie is its natural predator. According to Sun, an azure-winged magpie can eat 15,000 pine moths each year, thus protecting one mu (667 square meters) of pine forest.

But getting started was difficult.

The park set aside Bird Island, a 20,000-square-meter enclave, for the eco-project, introducing magpies and replacing all pesticides with expensive biopesticides.

There were the obvious problems, like birds flying away instead of staying put and catching insects.

"Keeping birds in the park while setting them free to catch insects was a big problem," says Sun.

They didn't have much to go on in their bird pest-control project.

There were successful cases off using azure-winged magpies in Rizhao City, Shandong Province, and at Dr Sun Yat-sen's tomb in Nanjing, Jiangsu Province.

But there was little written down for the park's reference.

"We only learned about some vague taming methods from stories of the early successful cases, then adapted them to our own situation," says Sun.

When the project began in 2002, the birds were raised in a huge cage on the Bird Island, but that changed after the terrible winter of 2003 when extremely cold temperatures caused respiratory infections in the birds. Only 60 of the initial 118 survived. That was the end of the cage.

"A bird expert told us that cage-raised birds are usually weak and vulnerable to environmental changes and suggested we let them free in the park," says Sun.

So, they were free as a bird, and some of them took off but most stayed around and were called back for feeding with a whistle. There were very few casualties.

To protect the birds from visitors and disruption, the bridge connecting the Bird Island to the main park was removed.

That was after the birds caught their own food.

The Bird Island is now a magpie haven but they can soar and feed throughout the 1.4 million-square-meter park.

"I often see azure-winged magpies flying or hopping about on the grass when I patrol the park in my electric cart," says Sun. "They move about and aren't afraid of humans."

Other birds are nesting in Century Park.

Five species have settled there since the magpies were introduced and Sun expects more visitors since the Yangtze River region is a stopover in migration from Siberia to Australia. Beneficial birds

Azure-winged magpies

Around 13,000 hectares of forest in Rizhao City, Shandong Province, were damaged by pine moths in the 1970s.

Tons of pesticide were sprayed by crop-duster aircraft from 1973-1975, but the moths survived, multiplied and became resistant.

The pesticide killed beneficial insects and birds.

Since 1982, 380 azure-winged magpies were tamed - they are natural predators of the pine moths - and introduced.

The damaged area has been reduced to around 7,000 hectares. Magpies have saved an estimated 100,000 yuan (US$14,637) in pest control costs °?- and they are non-polluting. Tiger shrike

A small bird up to 19 centimeters long, it has a tiger-like striped pattern on its upper body in reddish brown and dark brown. It makes a screeching (shrike-like) sound.

It's a predatory omnivore, eating insects, particularly grasshopper, crickets, beetles, bugs, butterflies and moths. It eats arthropods, tiny birds and lizards.

Great spotted woodpecker

One of the most common woodpeckers in China, it lives in woods throughout the temperate zone. A striking bird up to 26 centimeters long, it has bands of black and white that look like dots, the head and underside may be red.

It lands on a tree trunk and works its way up, eating arthropods and insects that bore into and damage trees.

It eats wood-boring larvae of moths and beetles, longhorn beetle, flathead borer and clearwing moth.

One woodpecker can eat around 1,500 pests a day. They are big eaters and just a couple can save a dozen hectares of forest in a winter. Dusky thrush

About 25 centimeters long, it's a dark-colored migratory bird, breeding in open woodland and wintering in south to Southeast Asia, especially China.

It feeds on locusts, wire worms, cutworms and larva of corn borers.