Discovery of new breeding pairs gives hope to Granite Island little penguin colony

Little penguin numbers on Granite Island have increased for the first time since fox attacks threatened to wipe them out, but researchers warn it is too early to say whether the population is recovering.

Key points:

The little penguin population on Granite Island has increased from 16 to 20

The burrows are filled with 10 different breeding pairs, including two new pairs

Researchers will be watching closely for any negative impacts from a new causeway to be opened in January 

A census last month discovered two new breeding pairs to bring the population up to 20 â€" an improvement on last year, when volunteers recorded the lowest-ever count of 16.

It followed devastating fox predation in the colony â€" numbered at 44 in 2018 â€" and sparked fears the little penguins on the island to Adelaide's south could be wiped out altogether.

Flinders University lecturer in animal behaviour Diane Colombelli-Négrel said two new nests discovered on the island during October suggested juveniles, who might have left before the fox attacks, had come back to breed.

"I was relieved that the numbers were not going down because there was always a possibility that we would have fewer penguins than we had last year," she said.

"I'm hoping this could continue to go up but at the moment I'm just cautious.

"There's a bit of fluctuation from year to year, simply because some birds do not breed if it's a bad year."

Diane Colombelli-Négrel is also planning to check on West Island's little penguin population.(Supplied)A beleaguered population

It is the second time in recent years that the little penguin colony has shown signs of improvement after a massive decline from about 1,600 in the early 2000s. 

The loss of penguins, which also occurred on nearby West Island, was attributed to a combination of factors but some experts believe a large-scale pilchard mortality event in the late 1990s was a big reason.

Little penguins on Granite Island burrow in breeding pairs.(ABC News)

Dr Colombelli-Négrel said a lack of food would have impacted their ability to survive and reproduce.

"But there's a lot of different factors that come into play and they vary between each of the colonies, which makes it harder to address the problem," she said.

"There's a combination of predation on land, as we've seen with foxes, natural seal predation at sea, but also environmental factors.

"We do know they're highly sensitive to changing sea surface or even air temperature when it gets really hot during summer."

The colony was showing signs of recovery through the mid-2010s â€" until the fox attacks of 2020 brought it to its knees.

Concerns over new causeway

Dr Colombelli-Négrel was now concerned about an influx of human visitors once the new causeway between Victor Harbor and Granite Island opened to the public.

The Victor Harbor Causeway is being built to replace what was a heritage-listed causeway.(ABC Radio Adelaide: Malcolm Sutton)

The concrete-and-steel structure is being built to replace the 150-year-old heritage timber causeway, and is expected to open in January.

Dr Colombelli-Négrel, who in 2019 called to keep the island off-limits to visitors at night during that year's breeding season, hoped a predator-proof fence to be installed on the causeway would be effective at keeping out foxes and stray dogs.

She also said that the construction, which had temporarily blocked access to the island, might have offered a little respite to the penguins from people.

"But obviously we're concerned about what happens once it is finished and then suddenly there's a big influx of people," Dr Colombelli-Négrel said. 

"It's hard to tell if it [the population increase] is a trend … or if next year they're going to go down again.

"That's why we need long-term monitoring."

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