Cause of penguin chick deaths still unresolved

What killed many threatened yellow-eyed penguin chicks on Otago Peninsula during the past breeding season is still a mystery.

But the Department of Conservation and the Yellow-eyed Penguin Trust are hopeful it is a natural fluctuation which will have little impact on the overall population.

Doc biodiversity assets programme manager David Agnew said the breeding season started positively, with an increase in the number of nests created by breeding pairs.

In 2007, 496 nests were identified, which had risen to 541 in 2008, continuing an upward trend that began in 2004.

"It was all looking good," he said.

A month later, after the chicks hatched, many from the northern part of Otago Peninsula began to die in their nests.

The losses were variable across breeding sites; in some, 50% of chicks died.

However, the public would not notice any difference in the number of penguins seen on beaches, he said.

About 80 dead chicks, brought in by landowners, were sent to Massey University for autopsies during a two or three-week period, Mr Agnew said.

Results of the autopsies had not yet come back, so the cause of the deaths was as yet unknown.

The answers were expected before the next breeding season.

Later in the season, many of the surviving chicks and some adults at breeding sites along the coast were lighter than usual.

Some of those chicks were taken into care and given supplementary feed to help fatten them up and give them a better chance at survival, he said.

Yellow-eyed Penguin Trust executive officer Sue Murray said that when the penguins were weighed in February before they fledged it was noticed many were lightweight.

Light was anything under 4.5kg.

It was not known what caused the problem, but it was not unusual to get "glitches" in breeding programmes some years.

Predation and disease had caused problems previously.

"There are always natural fluctuations. We'll be happy if it is one of those and it comes right again."

Mr Agnew said it was hoped this season's problems were the result of seasonal variation and would not have a long-term effect on the population.

"It might not have too big an impact on the overall population. If it was adult birds it would be more significant, but it primarily affected chicks."

As the penguins lived for about 22 years and had one or two chicks most breeding seasons, the population could sustain one-off problems, he said.

Work at Sandfly Bay to help reduce the human impact on penguins had seemed promising, with an increase in nests from about 8 to about 13, but many of the chicks died.

Mrs Murray said the high number of nests was positive as it was the number of adult breeding pairs which gave a true indication of the population.