The shocking total – described by wildlife charities as "a whole generation of seabirds" – comes just a week after the first reports of seabirds covered in a sticky glue-like substance being found on Cornwall and Devon beaches.
It is the second time in just three months that the substance identified by Plymouth University researchers as polyisobutene (PIB), which can legally be disposed of at sea, has killed hundreds of seabirds in the region.
"This can't go on," Tony Whitehead, from the RSPB in the South West, said.
"Wildlife charities, agencies and the Government must work together to impress on the International Maritime Organisation the urgency with which we need a total ban on the discharge of this stuff into our seas. Not in a year's time, or in five years' time, but now."
Dead and dying birds, mainly guillemots, have been found across a wide area, from Dodman Point in Cornwall to the Teign Estuary in Devon.
The worst hit area has been Whitsand Bay in South East Cornwall, where locals have been counting hundreds of birds every day. Another 200 birds are currently in the care of the RSPCA and South Devon Seabird Trust.
Zoologist and environment campaigner Alison Fogg, who lives by the sea near Lanteglos, on the south Cornwall coast, has been close to the unfolding disaster.
"Seeing over 157 dead birds on Lansallos beach, followed by hundreds more at Lantic Bay, was quite devastating," she said. "The scale of destruction to wildlife, in the beginning of the bird breeding season and at the start of the tourist season, is quite difficult to comprehend."
Harry Barton, chief executive of Devon Wildlife Trust, added: "Our region is famous for its stunning natural environment and clean beaches, and that is why we have such a successful tourist industry.
"The prospect of wading through piles of dead birds on the shore is hardly the advertisement we want. This is the clearest possible sign that our economy depends on a healthy natural environment.
"Pollution incidents like this can be prevented if the political will is there to do so. We must act quickly and decisively to stop this happening a third time."
It is not known whether the substance got into the sea as a spill from a ship or as part of legal and routine tank washing operations. It has not been established whether the current incident, and the one in February, are linked.
The wildlife trusts, RSPCA and RSPB have written to Shipping Minister Stephen Hammond calling on the Government to urgently raise the issue with the International Maritime Organisation (IMO). They want an urgent review of the hazard classification of PIB to prevent its discharge into the sea.
So far, more than 5,000 people have signed online petitions calling for a ban on the practice. Children at Fourlanesend Primary School, near Cawsand, some of whom have helped rescue stricken birds, are writing to Prince Charles urging that the dumping of PIB be outlawed.
St Ives Liberal Democrat MP Andrew George said an interim ban on the practice should be introduced, while a more detailed study was being conducted. Pressure could also be brought to bear, he added, on ports not to accept shipping which had not signed up to the moratorium.
Mr Hammond said the UK, along with other European countries, was "currently investigating the discharge of high viscosity products by chemical tankers and the resulting residues washing up on beaches".
The results will be sent to the IMO although campaigner remain concerned at how long changes may take to implement.
The Maritime and Coastguard Agency's (MCA) counter pollution branch is trying to pinpoint the PIB spill. A spokesman said: "The MCA is currently collecting data of the ships that passed through the area during a specific time frame, and looking through detailed cargo manifests. This is time-consuming and resource-intensive, but every effort is being made to try to determine the source."
