Standing on a white-sand beach at Florida's Gulf Islands National Seashore Thursday, blotchy stains from the Gulf oil spill could be seen creeping past the red-lettered "keep out" signs meant to protect nesting shorebirds.

And, according to conservationists, some well-meaning cleanup crews who unknowingly walk into nesting habitat may be doing more harm than the oil itself, experts say.

From April to August each year, rare shorebirds such as the snowy plover and least tern lay nests of two to three eggs directly on the softly undulating, open dunes about 40 feet (13 meters) from the water's edge.

Snowy plovers and least terns are considered threatened in Florida. When nesting, both species'