Pelicans will get a needed perk from the Folly Beach renourishment project: The hurricane-eroded Bird Key Stono rookery will be restored with sand at no extra charge.

That's not the case with Crab Bank, the vaunted shorebird rookery in Charleston Harbor. As much as $1.5 million must be raised by a private-public coalition in the next few months to renourish that island with sand diverted from dredging to deepen the harbor channel.

The cost difference has to do with pipes and barges, Army Corps of Engineers project managers say.

Bird Key Stono, off the southwest end of Folly Island, and Crab Bank are among only a few publicly owned rookery islands for threatened species of shorebirds protected in the state.

Each is considered critical to restore pelicans, egrets, black skimmers and other fliers because storms and erosion can wipe out any of the islands.

The birds are eye-catching wildlife along South Carolina's coast for residents and visitors alike, a draw to a tourism economy worth billions of dollars per year.

The $10 million Folly project, taking place from March to September, will replace 750,000 cubic yards of beach lost to hurricane erosion, from The Washout to Lighthouse Inlet Heritage Preserve at the island's east end. That sand will be piped from the Folly River on the island's west end. That's where Bird Key Stono sits.

Diverting 40,000 cubic yards of sand — the equivalent of 4,000 dump truck loads — to Bird Key Stono is expected to cost $300,000 of that money. Pouring sand on Bird Key Stono is just a matter of turning the pipes briefly the other way.

When the harbor is dredged alongside Crab Bank, though, pipes won't be involved. The sand will be loaded onto barges to be deposited at the mouth of the channel offshore. To renourish Crab Bank, pipes and different dredging equipment would have to be brought in, said Brian Williams, an Army Corps project manager.

"It adds to the cost any time you start adding another piece of equipment, or a different kind of equipment, or the contractor has to handle the sand more than once," he said.

So under federal rules, the $3 million price tag to renourish Crab Bank is extra and must be cost-shared, he said.

Conservation advocates would love to see the $529 million deepening project absorb all that cost, but "there isn’t any renourishment happening near Crab Bank, so there’s the rub," said Caroline Bradner, the land, water and wildlife project manager for the Coastal Conservation League.

The league is one of the members of the Coastal Bird Conservation Partners coalition, which is raising funds for Crab Bank.

Shorebird populations are in a steep decline across North America, said Nolan Schillerstrom, Audubon South Carolina coastal program coordinator.

The birds "are hanging on by a thread," he said, "and these protected nesting islands are one of the best chances we can give them."

Reach Bo Petersen Reporter at Facebook, @bopete on Twitter or 1-843-937-5744.

Science and environment reporter. Author of Washing Our Hands in the Clouds.