Lying dead between tyre tracks, it seemed obvious what had killed the little blue penguin found dead on Uretiti Beach.

It was an assumption that prompted Annette Laird to send the images to the Northern Advocate - one of two little blue penguins, or kororā, she had found dead on the beach.

"There's a lot of vehicles on the beach," she said. "People running their dogs from vans, hooning around in motorbikes and quads.

"The beach isn't the place for vehicles. We've got roads."

Laird, who is camping at the beach, said she wanted to see all vehicle use on the beach banned.

The mystery of the penguin death was solved through virtual autopsy by Massey University professor Dr John Cockrem.

His assessment was that the killer was quite likely to be more than one individual. In fact, Cockrem said higher sea temperatures and less penguin food was behind the penguins' death.

With this year's high sea temperatures being linked - in part - to global warming, it widens the suspect pool of those behind the death of the penguins considerably.

Cockrem said the birds had recently come out of a nesting period and were finding their way to sea for food.

Warmer water meant there was less food and this year's high sea temperatures had hit the penguins especially hard, with reports of dozens found dead on beaches from Auckland into the Far North.

Cockrem, who is studying the little blue penguins, said: "The photos indicate that the bird died of natural causes and had not been hit by a vehicle."

While it was difficult to pick an exact reason, Cockrem said it was likely "that bird has died because of a lack of food as a consequence of the incredible water temperature".

Meteorologists have been keeping a close watch on warming sea surface temperatures. Some pockets of water measured in October had reached 3C above average.

Another marine heatwave would mark the third in just four years - and these events are expected to become longer, stronger and more frequent under climate change.