Active little penguin burrows have been discovered on West Island south of Adelaide for the first time in seven years, six months after fox attacks put the population at nearby Granite Island in dire straits.

Both islands once supported thousands of the native birds, but seal and pest predation, as well as climate change, fish stocks and human interference, have been blamed for reducing their numbers to dangerous levels.

A recent census at Granite Island, for example, found 16 little penguins and eight active burrows remained a population left hanging by a thread after two foxes crossed the causeway in July and killed 10 birds.

"We were out at West Island a week-and-a-half ago and found two active burrows and, in one of those burrows, they were sitting on eggs, so they're actually breeding," Fleurieu district ranger Paul Unsworth said.

"It is hoped that with further success and establishment, this may be an important insurance population for the little penguins on Granite Island.

"Excuse the pun, but now we don't have to have all our eggs in one basket."

Mr Unsworth said a camera would be used to monitor the eggs, with little penguins typically producing one to two chicks at a time and sometimes nesting twice during a breeding season.

He said several little penguin pairs on Granite Island had also been found sitting on eggs.

"These are small, but good signs," Mr Unsworth said.

He said National Parks and Wildlife Service SA had been undertaking habitat restoration works on West Island for more than 17 years.

Mr Unsworth added that 50 adult Caspian tern had also been counted on West Island one of the few nesting habitats for the bird with 50 nests having fledged and another 39 eggs yet to hatch.

Mr Unsworth said West Island hosted several thousand penguins in the early 2000s and their decline, "like all things in nature", was attributed to a combination of events.

He said a large-scale pilchard mortality event in the late 1990s attributed to herpesvirus coincided with the big decline of the penguin populations.

"Obviously pilchards are food for these birds," he said.

"As a result the penguins have to travel further and they're more vulnerable to predation, exhaustion, and starvation."

Mr Unsworth said the recovering population of New Zealand fur seals would also have had an impact.

"They're recovering because they were hunted to near extinction last century," he said.

"They are a native species here and they do cop a lot of blame, I guess, because they are obvious."

Mr Unsworth said a gate had been installed at the end of the Victor Harbor causeway to prevent foxes making it onto Granite Island.

He said an ultrasonic deterrent had also been installed that emitted a high frequency that foxes and dogs did not like.

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Little penguins active on West Island near Victor Harbor for first time in seven years - ABC News