Also threatened are rare white-tailed eagles and eagle owls, which have ingested oil after eating stricken seabirds with oil on their feathers. The worst-affected area is a 22-mile stretch of coast in the north-west of the country, near the Gulf of Finland.
More than 3,000 dead birds, heavily coated in oil, have so far been collected from the polluted waters of the Baltic Sea. Local birds, as well as migrating species, have fallen victim to the spill.
But the true cost of the disaster is likely to be far higher , according to Vilju Lilleleht, a spokesman for the Estonian Ornithological Society. "The real number of deaths could be as high as 35,000," said Mr Lilleleht, adding that only about 10 per cent of bird casualties were ever found in the aftermath of oil slicks.
The spill of about 20 tons of oil, first noticed by authorities last Saturday as it spread through the coastal areas of Laane and Harju counties, south-west of the capital, Tallinn, was originally thought to have had a relatively limited impact on the local ecosystem. But temperatures of minus 20C have slowed attempts to save live birds and gather up those already dead.
Many of the birds are far out to sea and have taken refuge on thin ice, meaning that the rescue work is fraught with difficulties. One of the chief casualties of the spill is thought to have been the scarce long-tailed duck.
An Estonian ornithologist, Tiit Randla, said it was very hard to save the life of a bird that had come in to contact with oil. "When a bird's feathers are covered in oil it stops feeding and quietly fades away," he told the Baltic News Service. "In theory, a bird can be saved only if single feathers are oiled. We hope birds with few oil-covered feathers will lose them while moulting."
The source of the spill is still being investigated. The Baltic Sea is a busy shipping route, with many Russian oil tankers sailing to European markets. Estonian authorities have said that any one of 100 oil tankers could have been responsible for the leak, perhaps without even knowing it. They admitted that it was highly unlikely that the particular ship would ever be identified.