COVINGTON, La. (AP) — The dire impact of the massive Gulf spill was apparent Sunday on oil-soaked islands where pelicans nest as several of the birds splashed in the water and preened themselves, apparently trying to clean crude from their feet and wings.

Pelican eggs were glazed with rust-colored gunk in the bird colony, with thick globs floating on top of the water. Nests sat precariously close the mess in mangrove trees. As oil crept farther into the delicate wetlands in Barataria Bay off Louisiana, BP officials said Sunday that one of their efforts to slow the leak wasn’t working as effectively as before.

BP spokesman John Curry told The Associated Press on Sunday that a mile-long tube inserted into the leaking well siphoned some 57,120 gallons of oil within the past 24 hours, a sharp drop from the 92,400 gallons of oil a day that the device was sucking up on Friday. However, the company has said the amount of oil siphoned will vary widely from day to day.

Engineers are working furiously to stem the growing ooze as more wildlife and delicate coastal wetlands are tainted despite the oil-absorbing booms placed around shorelines to protect them.

A pelican colony off Louisiana’s coast was awash in oil Saturday, and an Associated Press photographer saw several birds and their eggs coated in the ooze while nests rested in mangroves precariously close to the crude that had washed in. Workers had surrounded the island with the booms, but puddles of oil had seeped through the barrier.

Meanwhile, three top Obama administration officials are returning to the Gulf Coast to monitor the spill response.

Anger with the government and BP, which leased the rig and is responsible for the cleanup, has boiled over as the spill spreads. U.S. Environmental Protection Agency chief Lisa P. Jackson was headed Sunday to Louisiana, where she planned to visit with frustrated residents.

Secretary of the Interior Ken Salazar and Secretary of Homeland Security Janet Napolitano were to lead a Senate delegation to the region on Monday to fly over affected areas and keep an eye on the response.

White House Press Secretary Robert Gibbs also told CBS’ ‘‘Face the Nation’’ on Sunday that Justice Department officials have been to the region gathering information about the spill. However, he wouldn’t say whether the department has opened a criminal investigation.

Meanwhile, the official responsible for the oversight of the month-old spill response said he understands the discontent among residents who want to know what’s next.

‘‘If anybody is frustrated with this response, I would tell them their symptoms are normal, because I’m frustrated, too,’’ said Coast Guard Commandant Thad Allen. ‘‘Nobody likes to have a feeling that you can’t do something about a very big problem.’’

President Obama also has named a special independent commission to review what happened. The spill began after the Deepwater Horizon oil rig exploded off the coast of Louisiana on April 20, killing 11 workers, and sank two days later. At least 6 million gallons of crude have spewed into the Gulf of Mexico since.