Eight endangered kiwi birds have died from respiratory infections while being treated at New Zealand's Wellington Zoo, in what authorities said on Tuesday was a "tragedy" for conservation efforts.
The eight birds were all juvenile rowi kiwi, the rarest sub-species of New Zealand's emblematic flightless birds, the Department of Conservation (DOC) said.
"Obviously zoo and DOC staff are devastated by the loss of the birds," DOC biodiversity manager Jo Macpherson said.
Kiwi numbers have been slashed by introduced predators such as stoats, rats and ferrets since European colonisation, with experts estimating only 70,000 remain.
The rowi sub-species is regarded as critically endangered, with only 400 left, although the population has increased from a low of 150 in the mid-1990s thanks to an intensive conservation programme.
The scheme involves volunteers scouring the South Island wilderness for rowi eggs, then taking them to hatch on a predator-free island, where the chicks stay until they are large enough to defend themselves and are placed back in their natural habitat.
Macpherson said the eight kiwis had been transferred from the island to Wellington Zoo so they could receive treatment for a gut parasite.
However, she said it appeared the parasite had weakened their immune system, making them vulnerable to a fungus found in bark that was used in the area where they were being housed.
"The bark has been regularly used at the zoo to simulate a natural environment with no adverse effects," she said. "This is an extremely rare and unfortunate occurrence and has come as a great blow."
Explore further: Early exposure to cat urine makes mice less likely to escape from cats