Images of oil-caked brown pelicans (Pelecanus occidentalis) have hit the front pages of countless U.S. newspapers and other media in the past week, driving home the still-growing impact of the Gulf of Mexico oil spill. So far, dozens of pelicans have been transported to rescue centers for treatment. The number is only expected to rise as the oil spill spreads and covers Louisiana's Queen Bess Island Pelican Rookery and other important breeding sites.

It is quite a blow for a species that was on the endangered species list until just six months ago. It had taken brown pelicans nearly 50 years to recover from the devastating effects of DDT and other pesticides that nearly wiped them out. In fact, the species was nonextant in Louisiana and had to be reintroduced to the area from a colony in Florida. Queen Bess Island, one of the primary breeding sites responsible for the resurgence of the birds, had to be stabilized after oil companies nearly destroyed the local wetlands so they could lay pipes.

So far, almost all of the oil-covered pelicans that have been treated have survived, something that would not have been possible without human assistance, a veterinarian with the U.S. Fish and Wildlife Service told The New York Times.

Crude oil like that present in the Gulf is particularly dangerous to birds. It coats their feathers and hardens, making it impossible for them to fly or even move. It also interferes with their ability to regulate their internal temperatures, leaving them susceptible to overheating and dehydration. It can poison the fish they eat, and the oil's toxins seep through the eggshells of pregnant birds, killing their embryos as well.

So far, the oil slick's impact is just starting to harm pelicans, although hundreds of other birds have been found dead. That does not bode well for a species we have already spent half a century trying to save.

Photo: Treated brown pelican being released back into the wild. U.S. Coast Guard photo by Petty Officer 3rd Class Nick Ameen