A PAIR of brown ducks with a flash of white serenely sailing on the Kowloon Park pond may not grab as much attention as the more exotic pink flamingoes standing one-legged by the water's edge. Yet these ducks are a testament to Hong Kong's little-known work - at least within the territory - on the worldwide breeding of species threatened with extinction. Its efforts came under the spotlight last week as the territory hosted the Southeast Asian Zoo Association's fourth conference at Hong Kong Park. The White-winged Wood ducks feature in Appendix One, the 'most in trouble' list under the Convention on International Trade in Endangered Species (CITES), meaning that trade in them is prohibited. 'It's one of the world's rarest ducks', with only about 200 left in the wild, says Kenneth Searle, honorary zoological curator with the Zoological and Botanical Gardens. It may seem a paradox that one of the world's densest urban jungles should be breeding rare creatures. Yet these four-month-old siblings, hatched in an incubator, are only two of many such ducks reared here. In 1985 the zoo sent 12 White-winged Wood ducks to the Royal Forest in Thailand, a gazetted national park on the Cambodian border. 'The Thais are on the point of releasing some into the wild,' Dr Searle said. The Kowloon Park flamingoes are a success story too. In four years, they had produced 34 young, of which only two had been hand-reared and eight had died, according to bird breeder Yeung Tat-shing. When he is not performing surgery in his Central clinic, Dr Searle is roaming the gardens checking on the birds and animals. He has been involved in the zoo's breeding programme since the 1950s. But the programme is not just a matter of putting male and female together and letting it all happen. For a start, it is internationally controlled. The International Union for Conservation of Nature and Natural Resources (IUCN) - the zoo is a member - keeps a database on what species have bred and when, and where the offspring have gone. Most problems revolve around mates disliking each other, abandoning eggs or the death of chicks. Yet a pair can be too successful at producing young. Preventing in-breeding - to maintain genetic diversity - is a major concern. 'We were asked [by the IUCN] to fit a contraceptive device to one of our prolific female Golden Lion Tamarins,' Dr Searle said. A project to re-introduce the beautiful animals - tiny monkeys with mini-lion faces - to forests in Brazil had been a success, with land owners queuing for the prestige of receiving them. But too many came from the pair and the busy parents had to stop. Dr Searle is waiting for the go-ahead to breed from the zoo's Laysan Ducks, following a turbulent history. That any are left in the wild is an amazing piece of luck. When conservationists went to save the species on the remote island of Laysan, they found one duck, a female. She had enough sperm in her oviducts to fertilise eggs. Two years ago a population of 500 ducks was recorded on the island. Yet the roller-coaster of life has sent the population plunging - a two-year drought slashed numbers to 38. Solutions are not obvious. Breeding of captive birds and releasing them would be pointless if lack of rain killed them. BUT having a captive population could mean the difference between extinction and survival - a point that the anti-zoo lobby would do well to remember, Dr Searle said. Zoo-rearing was moving closer to natural methods, even when it meant death, he said. The zoo's Red Crowned Cranes had two chicks this year. Both died in July's torrential rain. 'If it's hand-reared it thinks it's a person, it doesn't think it's a crane.' The same is true in the Edward Youde aviary at Hong Kong Park, says Yeung Chi-yan, senior amenities assistant at the Urban Council. For instance, a pair of Large Niltava flycatchers had twice hatched a chick but lost it. A Crowned Pigeon chick, its parents' fifth, had left the nest this week. The parents were helped with the infrastructure - a wire basket - after the huge birds failed to build nests in the trees. Yet even that intervention was not foolproof. A pair of Victoria Crown Pigeons were incubating eggs when their wire-and-straw home fell down. A pair of Crown Pigeons had caused staff their most difficult midwifery after abandoning an egg. Staff hatched it in an incubator but the chick died in 12 days, said deputy park manager Alex Chau Chung-yau. But deaths were few. The aviary had recorded about 80 births in 30 species, and had an annual death-rate of three per cent among 600 birds. Among its successes was the world's first captive breeding of the White Crowned Forktail, which the parents raised themselves. The most difficult species were parrots and pigeons, some of which needed hand-feeding for up to six months. At Ocean Park hand-rearing had been intensive, said aviary and butterfly curator Stephen Wong Pak-siu. Kept alone for up to 18 years except when performing four-a-day trick shows, the park's magnificent South American Macaws and cockatoos had forgotten how to rear young. Initial pairing results were spectacular - 'because they had waited so long, they copulated at once,' grinned Mr Wong - but the first few clutches of eggs were infertile. Finally they produced fertile eggs but sometimes treated them as food. Park officers learnt quickly about incubation, different protein formulas for different species and ages, and painstakingly fed the chicks every two hours. Results had been impressive. More than 550 young birds had been reared. Two Superb Starlings from Africa had produced their own chick - a feat for hand-reared birds. Next year Mr Wong wants to begin artificial insemination. One problem will be getting semen from a cock bird. There are other problems: a few weeks ago staff found a gigantic Burmese python which had successfully dined on a pheasant after arriving from the surrounding hills.