CHENGDU, China -- Though surprisingly not Japan's national bird, which oddly is the pheasant, the red-crowned crane, also known as the Japanese crane, has long been close to the Japanese heart. In China, too, it occupies a special place, along with the pine and turtle, as a symbol of luck and longevity, and often features in artworks, dances and songs.

Though best-known in Japan through those resident in Hokkaido, a separate population of red-crowned cranes -- which never crosses to Japan -- breeds in wetlands in Inner Mongolia, northeast China and the Russian Far East, and overwinters in the middle and lower reaches of the Yangtze River and around Poyang Hu lake in China's Jiangxi Province, as well as on the Korean Peninsula.

Last spring and summer, as an ornithologist I was able to spend four months observing these mysterious and graceful birds in the Zhalong Nature Reserve. An extensive wetland whose name means "cattle pen with lakes and grass" in Mongolian, the luxuriant 250-sq.-km reserve lying 27 km northeast of Qiqihar in Heilongjiang Province on the lower reaches of Wuyuer River is home to more than 250 species of waterfowl.

Foremost among these are the red-crowned cranes, of which there are thought to be only around 1,600 individuals left in the world. Regarded as barometers of ecological health, these birds are ranked in China's highest category of protected species and are listed as an endangered species in "Threatened Birds of the World" published by Cambridge, U.K.-based, BirdLife International.

Standing 120-160 cm tall as adults, with long thin necks and legs, and white plumage with black necks and flight feathers and a red "crown" of bare skin on the top of the head, the cranes live on open plains, in marshland and lakeside grasslands, and sometimes appear in farmers' fields. During migration periods, dozens of families often fly together, though at night when they like to settle on small marshy islands, each family stays apart from others.

However, whether resting or feeding omnivorously on amphibians, small fish, molluscs, insects and plants, a large adult bird will always act as a lookout, and cry "kulukulu kululu" to warn of danger. If the danger becomes more pressing, with its long neck vertical the lookout's cries become shriller and more urgent until the whole flock joins in in a tumult, ready to start running and flapping their long wings to get airborne.

Then, at the moment they take off and soar high in the air, these magnificent creatures appear more like supernatural beings than birds.

At Zhalong, such sights are there to marvel at from early March. That is when the first families begin arriving from the remote southwest, ready to mate and select nest areas which they will fiercely defend, crying continuously to announce their territorial claims. At this time, when fights between rival males occur, both birds stretch out their wings and charge, shrieking, and using their talons to claw violently at the other's chest until one backs off.

With their claims staked, when males are seeking a mate they cry "kuo-kuo-kuo," while females respond with "kuku-kuku-kuku." As part of their mating display, the males will often "sing" antiphonally with their beaks pointed skyward and flight feathers extended, vibrating, followed by a dancelike jumping performance.

Finally, pairs build up their crude, half-floating, dishlike nest of grass and reeds in an open marshland site with clear views around to prevent surprise attacks -- and almost always, it seems, at least 400 meters from any other. Two gray or brown- or purple-spotted gray-white eggs are usually laid as the weather warms up in May, hatching 30-33 days later.

From breaking out of their shells, red-crowned crane chicks can walk haltingly, and within five days they follow their parents by swimming in the shallows. Extremely caring, the mothers teach their young how to hide from enemies, how to look for food and how -- at around 10 weeks -- to begin to fly.

Though some of the cranes breeding at the Zhalong reserve have been ringed with international cooperation, much remains unknown about these birds' migration routes after they head south in September and October, and about their life cycles -- though they are believed to live for at least 25 years.

What is certain, however, is that the key condition for these birds to breed and overwinter are peaceful and safe wetlands with an abundant food supply -- which is why they are regarded as a barometer of wetland ecology spanning a whole swath of eastern Asia.