It's the fourth time the penguins have been disturbed by human intruders this season and the second time chicks have been killed this month. The attack comes after wildlife carer Kirsa Veal revealed her fear that animal cruelty was on the rise in the south-west after she attended to a possum and her joey, which later died, after they were dumped in a bag on the roadside in Monday's 44-degree heat.

Foxes and dog attacks were once the biggest threat to the survival of the dwindling penguin population but Warrnambool City Council's environmental officer David Williams said humans were responsible for the most recent fatalities on the island. Earlier this month two chicks were found dead after their nesting boxes were disturbed and in this latest attack four chicks were killed after their nesting boxes were upturned and their burrows trampled.

"I'm really disappointed," Mr Williams said.

"We've put a lot of work into the colony in the last few years and now people have come along and ruined it for everyone."

After dwindling to a dire population of just four in 2005, penguin numbers have rebounded in recent years under the success of a world-first program using trained Maremma dogs to guard the penguins from predators like dogs and foxes.

Mr Williams said volunteers and council employees had put thousands of hours into ensuring the success of the project and the survival of the precious little penguin colony on the island, which is closed to the public.

He said what made the attack worse was people had deliberately gone on to the island, despite signs and warnings the area was off limits to the public.

"The island is closed," he said. "Not only have they accessed the island illegally but they've harassed wildlife."

Mr Williams said anyone caught on the island would face a $500 fine and urged people to call police if they saw anyone illegally accessing the island.

Warrnambool City Mayor Michael Neoh said it was important for people to understand any part of the rock face and stairs on the island were out of bounds.

"It's disappointing because it's been such a successful program," he said. "I think it's fairly premeditated.There is signage indicating the project.''

"I hope people are more aware and refrain from going over to the island."