London ? Wildlife workers combed a 100-mile stretch of beach Thursday, trying to rescue birds covered in oil after thousands of gallons leaked from a stricken cargo ship off England’s southwest coast.

Half of the more than 1,000 birds that washed ashore in the past few days have been taken to wildlife centers around Lyme Bay, where the British ship, the MSC Napoli, was deliberately run aground last week after being damaged in a storm.

Most were guillemots – diving birds particularly vulnerable because even a spot of oil can make their plumage lose its waterproofing.

Contractors removed almost a third of the ship’s fuel Thursday, sucking the oil into a nearby tanker. The process was expected to last two weeks. That is longer than originally expected due to difficulties in extracting oil from the Napoli’s fuel tanks, two of which remain underwater, said Tony Redding, a spokesman for Zodiac Maritime Agencies Ltd. which operates the ship.

A new estimate from the International Tanker Owners’ Pollution Federation Ltd. put the amount of oil spilled between 17,000 and 30,000 gallons, Redding said.

The coast guard said the cleanup could last up to a year.