Muttonbirds are dying in their thousands nearly every year and much more frequently than ever before, washing up on the coast from Coffs Harbour to Tasmania.

On South Melbourne and Port Melbourne beaches on Wednesday beach cleaning contractor David Martinez picked up more than 150 short-tailed shearwater birds, a species of muttonbird. One day last week, he picked up a similar number.

Increasing frequency: Hundreds of Tasmanian muttonbirds, also known as short-tailed shearwaters, have been found in dead on Port Phillip bay beaches. Credit:Jason South

At Lord Howe Island this month, 200 shearwater birds washed up for the first time in many years, Monash University seabird biologist Jennifer Lavers said. These deaths en masse, known as "wrecks", have been reported along the coast from Coffs Harbour to Tasmania, she said.

The short-tailed shearwater birds migrate 10,000 kilometres from the Bering Sea, between Alaska and Japan, to Australian shores in late September to nest. Dr Lavers said they have eaten little on their journey and are exhausted by the flight.