A mystery disease is killing off yellow-eyed penguin chicks in New Zealand in a fresh blow to efforts to conserve the world's rarest member of the penguin family, a conservation group said on Thursday.
BirdLife International said the disease, which has baffled local scientists, had killed up to 80 percent of this spring's chick's in the worst affected areas on New Zealand's South Island.
"Most penguin chicks have been found dead at nests on Otago Peninsula and North Otago, with other outbreaks on Stewart Island and the Catlins coast," BirdLife said.
"With a global population of just under 5,000 birds, the yellow-eyed penguin is classified by BirdLife as endangered and is considered to be the world's rarest penguin species," it said.
BirdLife said New Zealand's Department of Conservation was running tests to try and pinpoint the extent and nature of the illness, which is thought to be caused by a strain of cornynebacterium.
It said there are more than 50 strains of this type of infection, one of which causes human diphtheria.
It said that the infection did not seem to be causing any harm to adult birds.
"This latest die-off is bad news for the world's rarest penguin species," said Barry Weeber, a senior conservation officer with BirdLife in New Zealand.
"Subpopulations on the southeast coast of the South Island and Stewart Island are already in decline and this will only add to the pressures this endangered species faces," said Weeber.
The main threats to yellow-eyed penguins include introduced predators such as domestic cats and loss of habitat.
BirdLife classifies three of the world's 17 penguin species as endangered -- meaning they are threatened with extinction -- and seven of them as vulnerable.