BEIJING, May 28-- All Chinese kids know the rhyme "Little Swifts", about migratory swifts' seasonal arrival in Beijing, but parents have never been able to answer the common question of where the birds have flown from. Until now.

New research has suggested that Beijing swifts, born in the capital in the eaves of old imperial palaces, travel more than 13,000 km without touching ground to winter in southern Africa before returning the following spring.

A group of Chinese, British, Swedish and Belgian ornithologists and bird lovers fitted tracking devices to dozens of the birds last May. So loyal are swifts to their nesting sites that the researchers were able to retrieve 13 of the devices on Sunday.

Data retrieved from them showed the birds headed northwest into Mongolia, then south through Iranand central Arabia into tropical Africa, before spending three months of the winter in Namibia and the Western Cape.

Swifts are among the fastest animals on the planet -- capable of flying at speeds of more than 110 km per hour. They spend almost all their lives in the air and they can feed, drink, mate and sleep on the wing, landing only to breed. As such, they are very difficult to study, confounding ornithologists speculating about their flight paths.

The typical life span of a swift is seven years, "which means the bird in its lifetime will cover a migration distance greater than 182,000 km, about half of the distance from the Earth to the Moon," said Terry Townshend, one of the researchers and founder of the Birding Beijing NGO.

"Swifts have a special place in the hearts of Beijingers," said Fu Jianping, president of the China Birdwatching Society. "Their screaming flights at dusk around many of our major landmarks are one of the most enchanting features of our summer."

The birds like to nest high above the ground. While many modern skyscrapers are deliberately designed not to accommodate birds, the flat surfaces of Beijing's gatehouses and the eaves of imperial pavilions are perfect for swifts. They can usually be found in the Forbidden City, the Lama Temple and the Summer Palace from mid-April to July.

While swifts have been visitors to Beijing for hundreds of years, their numbers in the city have declined dramatically in the past few decades. A 2000-2002 study by Zhang Zhengwang, professor of zoology at Beijing Normal University, found only 3,000 swifts in Beijing.

"The main reason behind the decline is that their breeding sites have been greatly reduced," Zhang said, noting that many gatehouses were torn down to make way for skyscrapers and wider roads. People have also strung nets on many old buildings to limit corrosion from bird droppings.

Conservationists are hopeful that understanding more about the birds' habits will help in their protection. "It will allow scientists to monitor these areas and identify actual and potential threats to the birds' population," said Townshend.

"In Beijing, we can begin to have conversations with developers to explore whether we can make new buildings more swift-friendly by including swift nesting places in the design," he added.