Unexplained chick losses on Stewart Island
The Yellow-eyed Penguin Trust has just completed the first year of a planned five-year study to measure the effects of cat predation on yellow-eyed penguins on Stewart Island’s north-eastern beaches. But instead of cat predation, what we found was an, as yet unexplained, high chick death rate.
Because of an apparent decrease in yellow-eyed penguin numbers on Stewart Island, the Trust, assisted by the Department of Conservation (DOC), was testing whether the loss might be attributed to predation by feral cats. During the 2003/2004 breeding season all nests along the Mt Anglem coastline were monitored intensely.
Early in the breeding season we discovered that chicks were dying at an alarming rate. Of 42 chicks hatched, only 11 were still alive by mid-February. This is a survival rate of just 26%. At some beaches every chick died.
There were no signs that these deaths were due to cat predation; instead starvation appeared to be the most likely cause of death. This possibility was tested by comparing the weights of yellow-eyed penguin chicks from the offshore islands of Bench, Tommy and Whenua Hou (Codfish) to those in the study area/main island.
Although the weights of chicks on the offshore islands were on average lower than those on the Otago Peninsula, the weights of the surviving chicks in the research area were comparable.
Observers monitoring the penguin chicks noted large pieces of regurgitated fish beside some of the dead chicks. Could this be a repeat of the mystery disease or biotoxin that killed off a significant proportion of the breeding population on the Otago Peninsula in 1989-90, or a widespread shortage of food?
At the moment we have lots of unanswered questions, although we’re hoping there may be some partial answers when analyses of samples and autopsies are completed.
These results highlight the importance of regular, ongoing monitoring of our penguins. “If the Yellow-eyed Penguin Trust had not been on Stewart Island this summer, we would never know this event had happened. The Department looks forward to working with them to determine what is actually happening with these birds and if there is anything we can do about it,” says Brent Beaven, DOC Programme Manager – Biodiversity, Stewart Island.
The Trust had already committed in principle to a five-year programme on Stewart Island, subject to finance being available. Although we feel it is important that our monitoring continues, we have not as yet been able to find total funding. This year’s work was largely funded by two, unexpected one-off grants. One was from the Community Trust of Southland, and the other from Contact Energy, as a result of Otago people using 10% less electricity to ensure adequate power supplies during early winter 2003. If you would like to consider helping fund this research, any donations marked Stewart Island Project will be earmarked for next season’s work.
