Griffiths Island in Port Fairy is again home to shearwaters, 40,000 in number.

The migratory birds have made their annual voyage to Port Fairy from the northern hemisphere.

The mass migration usually occurs during September but this year happened in the first week of October.

Friends of Griffiths Island chair Marten Syme said the change in arrival dates was interesting.

"They usually arrive by clock work on September 23, plus or minus a day," he said.

"But this year it was later, there was a gathering at the Island on October 4 and there was concern they hadn't arrived then.

"But they did come a couple of days after that. It's hard to know what caused the delay, it could have been a number of factors.

"There could have been a shortage of food from their migration point in the northern hemisphere which meant they needed to stay longer to get enough condition for the long journey.

"There may have been strong winds along the way which slowed them down or forced them to stop and rest.

"They may have found a really good feeding ground along the way, it's very much an unknown. The concern is they were late by quite a bit of time, although the positive is they still ended up coming."

Mr Syme said the many unknowns made making strong assumptions about the reasons behind the delayed arrival dangerous.

He questioned those laying the blame solely on climate change.

""I think it is clutching at straws that climate change caused this outcome," Mr Syme said.

"It could have been an unusual change of weather or just a quirk of nature along the way.

"Certainly if the arrival continues to be late in the coming years then we will get a better chance to work out what is happening.

"There will be some work for scientists to do going forward."

The round-trip migration to Port Fairy is 15,000 kilometres, with birds returning to the same burrows they had the previous year.

While in Port Fairy the shearwaters mate, give birth and guide their chicks through their formative days.

The adults depart Port Fairy in the middle of April and the young leave in early May.

Mr Syme said he had received reports of a number of dead shearwaters on the Island.

"Many of these birds are easy prey because they are exhausted," he said.

"Ravens are doing most of the killing at this stage which is what happens most years."

Mr Syme said baiting was in place to reduce the fox population on the Island, while a controlled shoot would also be held.