Rare birds fall prey to botulism

There are fewer than 1,000 black-faced spoonbills worldwide (Image: John Holmes/BirdLife)

By Alex Kirby BBC News Online environment correspondent

Dangerously high numbers of one of the world's rarest and most spectacular birds have died from disease in the last month.

An outbreak of avian botulism has killed 71 black-faced spoonbills in Taiwan since 9 December 2002.

This is more than 7% of the world population of 969 birds, according to BirdLife International.

The higher than usual winter temperatures that appear to have triggered the outbreak seem to be consistent with anticipated climate change patterns

BirdLife International

The outbreak follows a spell of unusually warm winter weather, and ornithologists think similar incidents could become common.

Avian botulism is caused by a water-soluble toxin produced by the bacterium Clostridium botulinum (in this case, type C). It is a potent neurotoxin.

Black-faced spoonbills breed on small islands off the west coast of the Korean peninsula and China.

Their main wintering wetland sites are in Taiwan, Hong Kong, Vietnam, China, Japan, Macao and South Korea.

Rapid help

A census conducted in January 2002 concluded the 969 birds found were the entire global population.

In the recovery suite (Image: Dr Fang-tse Chan)

The first dead birds were reported by the Wild Bird Federation of Taiwan (WBFT) on 9 December, and analysis showed avian botulism was the cause.

They were found in Taiwan's Tseng-wen estuary, the most important wintering site in the world for the birds with more than 70% of the global population.

WBFT, the Taiwan partner of Birdlife, and its local branch, the Wild Bird Society of Tainan, set up an emergency rescue team to try to save some of the infected birds.

The last dead birds were reported on 4 January, and 17 others have recovered so far.

The Taiwanese authorities and WBFT are working to minimise any recurrence of the disease at Tseng-wen by changing the way organic pollution is controlled.

They are also stockpiling type C botulism antiserum, which was used to help five sick spoonbills back to health.

Professor Chien-chung Cheng, the president of WBFT, said the loss of more than 7% of the world's black-faced spoonbills was "a significant blow to this already endangered species".

Pollution link

BirdLife says: "The higher than usual winter temperatures that appear to have triggered the outbreak seem to be consistent with anticipated climate change patterns.

"BirdLife fears more incidents of this nature may be expected to occur in future."

Spoonbills in Hong Kong (Image: Yu Yat-Tung/BirdLife)

The entire outbreak included three distinct waves of the disease, each following a sudden temperature drop.

Scientists think the earlier warm temperatures caused fishponds around the estuary to become eutrophic, a process in which the population of algae would have increased rapidly.

The colder weather could have caused a mass algal die-off, with the decomposing algae depleting oxygen levels in the water.

Hopes dashed

This would have killed fish and shrimps, providing ideal conditions for the bacteria to multiply rapidly.

The birds' endangered status means ornithologists think they face a very high risk of extinction in the wild in the near future.

But until 2001 they were classified by IUCN, the World Conservation Union, as "critically endangered", facing an "extremely high" extinction risk.

Their prospects, ironically, had actually improved with the establishment of a protected area in the Tseng-wen estuary in November 2002.