One expert says oil is affecting the natural habitat for many species.

Enlarge By Win McNamee, Getty Images An oil-drenched brown pelican floats in Barataria Bay near Grand Isle, Louisiana. BURAS, La.  As BP made progress containing the Gulf of Mexico oil spill over the weekend, the number of birds hobbled by the oil increased at an alarming rate, indicating the oil is spreading farther into sensitive marshlands. The Fort Jackson Oiled Wildlife Rehabilitation Center here has treated 203 oiled birds, many brown pelicans, since the center opened six weeks ago. Of those, 110 have arrived since Friday, said Jay Holcomb, executive director for the International Bird Rescue Research Center, one of two groups tasked with cleaning the ailing birds. At least 75 oiled birds across the Gulf Coast have died, according to statistics compiled by the Coast Guard's Unified Command. Animal rehabilitation groups and the U.S. Fish and Wildlife Service have also rescued 28 oiled sea turtles. "This really increases the urgency of efforts to shut off the leak," Holcomb said. Admiral Thad Allen, the federal incident commander, said Sunday that BP had made some progress toward containing the leak, but added that even after the spill is contained, oil will remain in the Gulf "well into the fall." PHOTOS: Animals, fish drenched by oil DOLPHINS: Deaths investigated by environmental officials CEO: BP chief says he won't quit over Gulf spill "This is a siege that is going to go on for a long time. We are spread from south central Louisiana over to Port Saint Joe, Florida," Allen said Sunday on CBS' Face the Nation. "It is not going to end soon." A cap and siphon system installed last week over the ruptured Deepwater Horizon well is now capturing about 420,000 gallons of oil a day, BP officials say. Scientists have estimated that 500,000 to 1 million gallons of oil a day are gushing from the well. The gusher will not stop until BP completes drilling a relief well, can divert the oil and plug the broken well with cement, Allen said. Meanwhile, technicians at the bird rehabilitation center spend up to an hour cleaning each bird, first rubbing it with vegetable or canola oil to break up the crude oil, then washing them with warm water and detergent. The inside of the bird's beak and gullet must be scrubbed, too, Holcomb says. Typically, as many as half the birds die while in captivity, although the survival in this spill appears to be higher, he says. Seeing the oiled birds is "very heartbreaking," says Doug Inkley, senior scientist for the National Wildlife Federation, but he's troubled most by what isn't visible. "The vast majority of impacts to fish and wildlife you will never see because it's occurring under water." Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more