Beachgoers in Alabama who descended on the breeding ground of a threatened seabird species this summer scared adults away from their nests and used the eggs to decorate the sand, most likely killing hundreds of chicks, wildlife experts say.

The exact number of least tern birds that died in Mobile Bay is unknown, but it was “a tragic loss of a colony that size,” said Katie Barnes, a senior biologist at Birmingham Audubon who oversees the protection, monitoring and surveying of Alabama’s coastal bird species.

Least terns, which are protected by the federal government under the Migratory Bird Treaty Act, often lay their eggs on wide-open beachfronts, digging shallow nests beneath the sandy surface. The diminutive birds — adults weigh just 1.5 ounces — are considered a threatened species for several reasons, including beach recreation, Ms. Barnes said.

“They’re very sacred to us because they are so sensitive,” she said.

Although the least tern population in Alabama is not endangered, as populations in other locations are, the birds there have still struggled with habitat loss and sea level rise.