Environmental workers crawled on their hands and knees Saturday to clean up a narrow 4-mile-long oil spill that threatened the nesting grounds of an endangered bird along the Cape Cod National Seashore.

The 6-inch-wide spill ran from just north of the Nauset Beach lighthouse up to 4 miles south to Nauset inland, Coast Guard petty officer Ellen Marie Harrington said.The spill left a ribbon of marble-size tar balls of No. 6 oil at the high tide mark running through the nesting area of the piping plover, anch-long bird.

The beach hosts about six mating pairs of the bird, one of the largest concentrations on the Eastern Seaboard, National Park Service ranger Michael Whatley said. Apparently warned away by cleanup workers, the birds had relocated behind some sand dunes, he said.