Dozens of chattering shorebirds—punctuated by the odd pelican—are relaxing on this shallow strip of land in Breton National Wildlife Refuge, known as one of the most important bird breeding grounds in the world. (See pictures of places that could be America's next national parks.)

After heavy rains, experts from a handful of conservation groups traveled by boat Monday to see if oil from the ongoing Gulf of Mexico spill had yet reached the birds at this remote spot. (See a map of Louisiana's barrier islands.)

So far, nothing.

But a heavy band of oil