The oiling of birds is usually one of the most dramatic visual effects of an oil spill. The toxicity of the oil ingested during a bird's attempts to remove the oil from its feathers usually results in the death of the animal. Very few of the birds recover, in spite of heroic efforts by rescue workers. There appear to be no long-term effects on the bird population; their numbers rebound rapidly within a year or so. For example 35,000 dead birds were retrieved as a consequence of the Exxon Valdez spill, and the total death toll was much higher-close to 200,000 birds, including about 200 adult bald eagles. However in one year's time it was observed that a significant number of birds occupied areas that had been oiled and, more specifically, 51% of the bald eagle nests in the oiled region were occupied and produced an average of 1.4 eaglets per nest, the usual ratio for this area.

It was demonstrated that ingestion of sublethal amounts of crude oil by herring gull chicks causes several sublethal effects that could impair the ability to survive. In this study the chicks suffered liver effects and ceased to grow in comparison to similar chicks that had not ingested oil. A similar study on young herring gulls and puffins showed oxidative damage to the hemoglobin of their red blood cells. Thus it appears unlikely that birds that have been subjected to a large amount of oil will survive for long even if the oil covering their feathers is removed. These birds will have ingested oil in their attempts to remove it from their feathers and consequently will be subject to its sublethal toxic effects.

0 0

Post a comment