Some of the most beautiful and rare types of birds, ranging from the Norfolk Island green parrot to the Mauritius parakeet, were critically endangered in 1994 with populations less than 100. Dr Stuart Butchart, an expert with the British-based group BirdLife International, has now conducted a global audit of 27 of the threatened species.

He and his colleagues found that 16 of the 27 species, that would have become extinct by 2004, were saved by conservation efforts. Their numbers began increasing lately. International cooperation and adequate funding can thus halt and even reverse a worldwide decline in bird types.

"These successes show that preventing extinctions is possible, given political will and concerted action," Butchart said. "We need to scale up our efforts considerably to prevent wholesale biodiversity loss and many more extinctions in the coming decades."

Two of the most dramatic examples of conservationist successes have been the Norfolk Island green parrot and the Californian condors.

In 1994, there were just 4 breeding females and as few as 28 males of the Norfolk Island green parrot. The birds had their habitat destroyed by human building, were hunted by rats and feral cats and were threatened by disease. Conservationists set up a system of nest protection and protected the birds from the predators. By 2004 their numbers had grown to at least 300.

There were only 9 Californian condors in 1994. Scientists were "certain" of their imminent extinction. The birds were dying of lead poisoning after eating carcasses of animals killed with lead shot. Moreover, the birds are also hitting the power lines spread across their natural habitat. Conservationists succeeded in obtaining a ban on hunting in their habitats and as a result they have now reached a population of 128, including 44 adults.

In spite of these successes experts warn that far more is needed for protecting biodiversity. The 16 species in the study represent just 1.3 percent of all those threatened with extinction. Almost half - 45 percent - of all species under threat have suffered a decline since 1994. If current trends continue, more than 1,200 different types of bird will become extinct during the course of the 21st century.

Nonetheless, the study shows that the decline in biodiversity is not unavoidable. Conservationist efforts can be successful.