Beachgoers on the east coast are faced with a devastating sight of hundreds of dead mutton birds on the coastline

Beachgoers have spotted a creepy sight along Australia’s east coast this week, as hundreds of dead birds have washed up along the coastline.

The birds are short-tailed shearwaters, or sheepbirds, which undertake a marathon migration each year from Alaska, along the California coast and across the Pacific Ocean to Victoria and Tasmania.

One person said his friend had collected more than 150 birds from beaches around Sydney alone.

Every year some birds of course do not continue the migration due to exhaustion, but why the birds have perished in such large numbers in recent years is not definitively known.

Scientists have a number of theories, some suggesting that weather, such as wild winds or heat waves, could have disrupted their migration, while others suggest that climate change and warmer ocean temperatures have made their fish food source scarcer.

Wildlife charity WIRES and research group Adrift Lab said they had received “numerous” reports of the birds this week from several beaches in NSW, including Palm Beach, Collaroy and One Mile Beach.

Some people added that they found some birds alive and tried to rehabilitate them but were unsuccessful.

Both groups added that if anyone finds similarly stranded birds, they should be contacted so they can keep track, as there is no official way to document numbers.

It is not the first year that there has been a mass stranding of these birds, called a ‘wreck’, with similar events happening on a smaller scale every year, along with a much larger one in 2013.

Researchers from the University of Tasmania attribute the 2013 event to a combination of a severe marine heatwave that year called ‘The Blob’ and competition with salmon, released into the wild by commercial hatcheries, for reduced food sources.

The birds complete one of the longest migrations in the world, from Alaska to Tasmania

Dr. Adrift Lab’s Jenn Lavers told ABC Radio that warming waters and marine heatwaves have affected the bird’s ability to find food.

Scientists from the University of NSW and CSIRO this month discovered a massive 400km-long sea gyre off the coast of Sydney, circulating warmer-than-normal water.

‘Fish move to other areas or move further into the water column where it is cooler and therefore out of reach of seabirds and other species,’ says Dr Lavers.

‘These are definitely not the birds that are blown off course by the wind. They thrive in the windiest parts of our planet.

‘These birds are on a long migration and are exhausted. If they can’t find food, they may become too weak to fly as they normally would and be blown off course, but it’s not the wind itself.

“These wreck events were extremely rare, now we are seeing them in consecutive years.”