gannetBP’s vast and spreading oil disaster is killing ever more birds and other wildlife in the Gulf of Mexico — but one of the worst spills for birds was a harmless-sounding 5 tonnes of oil in the Baltic Sea in 1976.

That spill from a ship killed more than 60,000 long-tailed ducks wintering in the area after they fatally mistook the slick for an attractive patch of calm water, according to Arne Jernelov, of the Institute for Futures Studies in Stockholm, writing in today’s edition of the journal Nature.

By contrast, he writes that fewer than 1,200 birds have  so far been recorded killed after the explosion of the Deepwater Horizon rig, which has led to a leak of a gigantic 250,000 to 400,000 tonnes of oil in the Gulf of Mexico.  About 60,000 birds were killed off Alaska in 1989 by the accident usually known as the Exxon Valdez spill (…Exxon’s website calls it The Valdez Oil Spill ), previously the biggest spill off the United States at 37,000 tonnes.

By my maths, the Baltic Sea spill killed one bird for about every 80 grams of oil (…an amount easily spilt when filling up a car), the BP spill (so far) one per 200-330 tonnes. Even tiny amounts of oil can mean that birds’ feathers stick together and let chill water, like in the Baltic Sea, get to their bodies through what is normally a layer of insulation. They can then die of cold.

Jernelov gets backing from the Global Marine Oil Pollution Information Gateway, linked to the U.N. Environment Programme.