South West sea birds 'probably killed by PIB'
A substance thought to be responsible for the deaths of more than 350 birds is probably the same as that which affected hundreds earlier in the year, experts have said.
Scientists from Plymouth University said they were "almost certain" it was polyisobutene (PIB).
It is often used by ships to make their engines work more efficiently.
The Maritime and Coastguard Agency (MCA) said it would try to determine the source.
Hundreds of birds have been found on beaches in Devon and Cornwall since Wednesday.
The RSPB South West, which is trying to calculate how many birds have been washed up dead, tweeted that so far, 40 were found at Par, 157 at Lansallos, near Polperro, 139 at Seaton, in Cornwall and 25 at Wembury.
On one section of beach between Downderry and Seaton more than 100 birds, including guillemots and gannets, were found dead on Sunday morning.
Since Wednesday, more than 170 birds have been taken to the RSPCA's centre at West Hatch, near Taunton, but 58 have died.
The South Devon Seabird Trust said it was looking after 12 birds.
In February, more than 300 birds, mainly guillemots and some razorbills, were rescued after they were covered in the substance, which the MCA said was a "fairly common chemical" carried aboard ships.
Sheryll Murray, the Conservative MP for South East Cornwall, said: "It's tragic not only for the wildlife, but also because we are a tourist constituency."
Most of the birds are guillemots, but razorbills, puffins, gannets and cormorants have also been found dead.
Claire Wallerstein, who has been collecting the birds for the community project Rame Peninsula Beach Care, said: "It's really heartbreaking.
"It's like something from a horror film with bodies strewn across the beach.
"A few days ago we were picking up live birds, but now nearly all of them are dead."
Jo Barr, from the RSPCA, said some of the birds which were rescued in February, had been found again covered in the sticky substance.
The RSPB has called for polyisobutene, which can be released legally under certain conditions, to be reclassified and discharges of the substance to be outlawed.
The MCA said: "We are liaising with partner agencies to find out the extent of the problem and, if at all possible, to determine the source."
Steve Hussey, from Devon Wildlife Trust, said: "This is something that actually impacts our economy here in the South West.
"We're very reliant on our natural assets and a clean sea is one of those.
"If you're making a decision as to where to go on holiday and where to spend your cash and you're seeing pictures of dead birds being washed up, that's not a very good message."
The RSPCA has urged people to contact them, rather than try to help any injured or distressed birds.
Dog walkers have been warned to keep their pets away from dead or injured birds.