Most waved albatrosses are on Espanola

The archipelago is what scientists refer to as an endemic bird area: a location where at least two species breed that can be found nowhere else.

BirdLife International, a conservation alliance working in more than 100 countries, has identified the Galapagos species it believes are in most danger. It fears the slick is heading south towards Espanola Island.

Birdlife is concerned for some relatively abundant species also found in the Galapagos, including the swallow-tailed gull, brown pelican, blue-footed booby, red-billed tropicbird and white-rumped storm petrel.

The five species it is most worried about are:

• Lava gull: vulnerable. There are only 600-800 birds all told. The gull is a scavenger, and lives on eight islands in the group.
• Galapagos penguin: endangered. The only penguin species in the world that lives near the equator. In 1999, it numbered about 1,200 birds. Oil spills are a serious threat, as it forages within 10 kilometres (six miles) of the shore, and can be affected when it dives for food. The penguins reproduce slowly, and many young birds die. Most of the penguins live some distance from the spill, but some colonies are closer.
• Waved albatross: vulnerable. There are thought to be just over 36,000 birds altogether, with 99% of them breeding on Espanola. Birdlife says modern long-line fishing vessels operating off the Galapagos may also be a serious threat to the species, another scavenger, which will happily eat other birds or fish killed by the oil.
• The flightless or Galapagos cormorant: endangered. A 1999 census found only 900 birds, which Birdlife says are "extremely susceptible to catastrophes such as oil spills".
• Galapagos petrel: critical. This species declined very rapidly in the early 1980s, in some cases by as much as 81% in four years. The latest population estimate puts its numbers somewhere between 20,000 and 60,000 birds.

The Galapagos penguin breeds slowly

"Endangered" means that it faces a very high risk of extinction in the near future. "Critical" denotes an extremely high extinction risk in the immediate future.

Grahame Madge of the RSPB, the UK arm of BirdLife, told BBC News Online: "The lava gull is the one we're most worried about at the moment.

Jeopardy increasing

"It's the rarest of all the world's gulls, which number about 50 species. It faces no other threats in the Galapagos, but this incident is a real threat to a bird with such tiny numbers.

"The gulls are seashore specialists, and they need quite a big territory. Wherever the oil comes ashore, it will affect them, and they'll be eating oiled fish as well.

"If more than 30 or 40 of them die, we'll probably have to reclassify it from vulnerable to endangered."

Photographs courtesy of Andy Swash