The mystery of why dozens of dead birds are being found washed up on beaches along the NSW coastline has been solved.

A photo of a bird half-buried in sand prompted locals from Sydney‘s Northern Beaches to question why so many corpses had been spotted.

The Northside Emergency Veterinary Service provided a definitive answer in a post on its Facebook page – explaining the mass deaths were a yearly phenomenon.

‘We’re seeing large numbers of shearwater seabirds (also called muttonbirds) washed up along local beaches, primarily due to exhaustion and starvation,’ it said.

‘This is due to the challenges of their intense annual migration between Australia and the Northern Hemisphere and reduced availability of food, likely related to climate change.

‘Unfortunately if a shearwater bird is too weak to fly, sadly it’s unlikely to recover.’

Locals debated whether the effects of climate change was causing the death of more birds than previous years.

‘It happens each year but researchers have found the death rate has been climbing,’ one person commented.

Locals on Sydney's Northern Beaches questioned why some dead birds were washing up

Locals on Sydney’s Northern Beaches questioned why some dead birds were washing up

The Northside Emergency Veterinary Service provided a definitive answer to why so many dead birds were washing up on Sydney beaches - revealing it is a yearly phenomenon

The Northside Emergency Veterinary Service provided a definitive answer to why so many dead birds were washing up on Sydney beaches – revealing it is a yearly phenomenon

‘Climate change has meant there is less food for the poor birds and they are dying from malnutrition. Very sad.’

Some shearwater birds travel up to 15,000km during their annual migration between nesting areas in the southern and northern hemisphere.

The birds need to be at full strength to make the mammoth trip over the Pacific but the fish they feed on have apparently dwindled due to sea temperatures rising.

Anyone who finds a stranded or weak shearwater should contact a licensed wildlife rescue and rehabilitation group or the nearest vet.

Pets and children should be kept away from distressed birds.

If a bird is found with a metal ring on its leg, people should report the number to the Australian Bird and Bat Banding Scheme.