A wildlife pathologist investigating a mystery illness killing Dunedin's yellow-eyed penguins says the sickness is attacking the birds' red corpuscles.

Massey University senior lecturer and wildlife pathologist at the university's specialised veterinary hospital, Stu Hunter, had ruled out lead poisoning or hydrocarbon poisoning - usually the culprits in cases where the red blood cells of species were under attack.

Hunter, who carried out more than 1300 post mortems on oceanic wildlife killed during the Rena oil spill in 2011, said trying to find the cause of 61 penguin deaths on the Otago Peninsula over the past three months was a frustrating exercise for which he had sought help from overseas colleagues.

Post mortems had been carried out on 20 or more adult bird corpses, Hunter said. The penguins were possibly poisoned by some kind of biotoxin from algal blooms in the ocean.

"When we do the post mortems they're not showing too much. They're all healthy looking birds with lots of muscle and fat," Hunter said.

"But when I look at the tissue under the microscope, it looks like something's destroying their red blood cells. Yeah, we're just not sure what's doing it. There are a number of things that will do it but the usual causes aren't turning up."

Hunter said his feeling was the cause was something toxic rather than infectious because there was no evidence of inflammation in the dead birds.

"But the test we've run so far on heavy metals and a few of the marine biotoxins have also turned up negative. Nothing really seems to fit very well."

The majority of birds had no stomach contents (apparently due to vomiting) so scrapings of mucus were now being taking from stomach linings as scientists continued with tests.

Meanwhile, Dunedin Visitors Centre manager Louise van de Vlierd said the penguin deaths were not affecting numbers wanting to visit sites. Tourist interest in the critically endangered species - among the two rarest penguin types in the world - remained significant, she said.

Tourism Dunedin moved quickly this month to assure tourists there were still plenty of yellow-eyeds to see at various viewing sites on Otago Peninsula despite the outbreak of the fatal illness.

The organisation said the deaths occurred mainly in ones and twos across the area's 15 breeding sites, so losses were spread out and not obvious at most locations.

- D Scene

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