The dead shearwaters have been sighted in Bondi, Collaroy and Cronulla, sparking concern over an unusually high number of bird deaths.
The birds are making their annual 14,000km trip from Alaska to southern Australia, and it is common for some to die of exhaustion during the journey.
However, reports of 'hundreds' washing up have caused alarm from concerned residents, and come after birdwatchers in Victoria recorded fewer shearwaters than usual arriving after the lengthy migration.
President of BirdLife Warrnambool Peter Barrand told Yahoo News Australia only half the expected 30,000 birds had returned this year, with many in a poor condition.
Mr Barrand explained that with rising sea temperatures, it would be become harder for the shearwaters to feed during their flight as the fish they usually ate would not venture into the shallows.
In a statement on their website, BirdLife Australia said: 'Reports are coming in of an unexpected number of Short-tailed Shearwaters washing up on Sydney’s beaches.
'So far, the birds have been found beachcast on the sand from Manly south to Cronulla, but it is unclear whether it's a localised event or a more extensive phenomenon.'