Penguin deaths under investigation
During routine fieldwork this summer a total of 160 dead adult penguins were found on four coastal islands between 23 November 2001 and 15 January 2002. Over half of these birds were found at Welch Island. The dead penguins were on the sea ice close to the islands at the seaward side of colonies and within the colony on Welch Island.
Amongst a population of over 80,000, 160 dead penguins is not a lot of birds, but usually we find only one or two dead adults each breeding season. We suspect many deaths occur at sea and so remain undetected. The only other instance of penguin deaths on such a scale occurred in the Mawson region in 1972.
The penguins all appeared outwardly healthy on their return to the breeding grounds after their winter feed. There were more birds than we've ever seen before along this coast – 10 percent higher than our previous high in 1997-98 – and more chicks than we've ever had in the 12 years of the monitoring program.
The majority of dead penguins were found between 23 November and 11 December 2001. These deaths coincided with egg laying and early incubation.
Preliminary investigations suggested disease as a cause, but this will be known only when the analysis of tissue samples is completed in Australia. Location of the dead birds is evidence for a naturally occurring cause: three of the four islands are rarely visited by humans. In addition, stringent measures were implemented to minimise the possibility that infectious material is transferred between penguin colonies by humans. These measures included the washing of boots on arrival at and departure from the penguin colonies.
These penguin deaths are not linked to the major penguin breeding difficulties at Ross Island. The sea ice extent at Mawson in 2001–02 was fairly typical although poor weather prevailed throughout November and December.
STOP PRESS: Evidence from the post mortem examination of birds returned to Australia from Welch Island suggests that the majority of birds died from injury probably sustained among the broken ice at the island's edge. No evidence to implicate disease as a cause of death has been found.
Lyn Irvine, Antarctic Marine Living Resources Program, AAD