Six hundred sea birds are likely to have died as a result of oil leaks from a beached cargo ship, the Royal Society for the Protection of Birds said.
The RSPB said that more than 1,000 sea birds have been contaminated by oil from the MSC Napoli, which has leaked more than 200 tonnes since it was deliberately run aground off the Devon coast at the weekend.
The Royal Society for Prevention of Cruelty to Animals has also reported large numbers of contaminated birds and has picked up a further 50, bringing their total to 498.
Salvage teams are currently working to pump out the oil the Napoli is carrying. Maritime and Coastguard Agency (MCA) spokesman Mark Clark said that it was being pumped at the rate of 28 tonnes per hour - the vessel has 3,500 tonnes on board.
The RSPB said they felt the situation was "calming down" after hundreds of contaminated birds were reported to them in the last three days.
"We have had in excess of 1,000 reported to us, mostly guillemots," a spokesman said. "And therefore we can estimate that around 600 are likely to have died.
"Once guillemots have oil on their feathers they are no longer waterproof which means they cannot feed.
"Gulls have a better chance of surviving because they can scavenge for food."
The 62,000 tonne Napoli, which has structural faults following a storm in the Channel last week, was grounded a mile off Sidmouth, east Devon, at the weekend.
Water testing near the Napoli showed the area has not, so far, suffered any pollution from pesticides and other chemicals carried on the ship.
