Saving species in Hong Kong

Scientists put up nest boxes as trees with cavities birds need disappear.

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Above the teeming shopping streets of Hong Kong's Causeway Bay district, a fight to save one of the world's most endangered species is unfolding high in the branches of a decades-old cotton tree.

Nestled among its sprawling boughs is a nest box designed for the yellow-crested cockatoo, of which only 1200 to 2000 remain in the world.

Although the birds are native to East Timor and Indonesia, one-tenth of those left are found in Hong Kong - one of the "largest cohesive remaining wild populations" globally, according to Astrid Andersson, a postdoctoral researcher at the University of Hong Kong.

Their future now hangs in the balance, due to habitat loss and, some suspect, a black market for the rare birds.

The cockatoos' numbers have stagnated, with far fewer juveniles than when Andersson began monitoring almost 10 years ago.

The birds don't make their own nests but depend on natural cavities in trees - about 80% of which have vanished in recent years, because of typhoon damage and government pruning.