King penguins are recolonising the Macquarie Island Isthmus almost 100 years after the populations were slashed by commercial harvesting.

Between 1810 and 1918 birds from the two large breeding colonies, at Lusitania Bay and the North-End Isthmus, were killed for the blubber oil trade.

The North-End Isthmus colony was totally wiped out, while at Lusitania Bay numbers were reduced to fewer than 5000 birds.

Observations by the Australian Antarctic Division have found that while the Lusitania Bay site was rapidly recolonised, the Isthmus remained abandoned until recently.

Biologist John van den Hoff said king penguins usually return to their natal (birth) colonies and because the colony at Lusitania Bay was never totally eradicated the birds filled that area first.

In 2000, the population at Lusitania Bay was estimated at 170,000 breeding pairs forcing the expanding colony to seek other suitable breeding habitat.

“Up until 1995, no breeding colonies had been observed on the Isthmus at all but now a small colony has established itself at the southern end of the Isthmus at Gadget Gully,” Mr van den Hoff said.

“Initially the number of birds attempting to breed was low and chick mortality was high, but by August last year, 235 chicks were present,” he said.

The population at Gadget Gully is also of interest from a climate change perspective with one of the most severe El Nino events occurring in 1998 when the colony failed to raise a chick.

“So this colony provides us with a great opportunity to gauge how the penguins might respond to climate change in the future,” Mr. van den Hoff said.

It is hoped the population continues to grow and other previously abandoned breeding sites on the island will be reoccupied in the future.