SAND ISLAND, Ala. >> Beach volleyball players on a small island off Alabama probably killed hundreds of unhatched birds, moving eggs to make room for their playing court and scaring adult birds from nests, according to Birmingham Audubon.

The day after the damage was found, the conservation group put up ropes and signs to tell people about the Sand Island rookery of federally protected birds called least terns — and the education has worked, Katie Barnes, chief biologist for Birmingham Audubon’s Coastal Program, told AL.com .

The rope, strung between posts, is called “symbolic fencing.”

“Ever since we put the fencing up, everyone has been very respectful. We have not seen a human footprint in the area. Boaters have not pulled up to that area,” she said.

Least terns are white birds with black caps. They’re half as big as cardinals, weigh less than 1.5 ounces (42 grams) and lay eggs in shallow depressions on the sand.

The damage was discovered over the Fourth of July weekend by Andrew Haffenden, who was a wildlife researcher in his native Australia and was conducting a bird survey for Birmingham Audubon on a small spit that juts off the south side of Dauphin Island.

“I’d seen swirls of birds out there … and then on Fourth of July weekend, I counted 17 boats out there on that island, so I was pretty disturbed,” Haffenden said. “I had been wanting to get out there, and looking through my scope, I could see the volleyball net and the tents.”

He and others went out in a boat and found the nesting birds, and then piles of eggs.

Not only did the volleyball players remove all the eggs from nests around their net, they “actually made a little dome of sand and placed the eggs around it to decorate it,” he said.

With 17 boats around the island, he estimated that hundreds of birds would have left their nests to avoid the people watching the game.

Beach-nesting shorebirds sit on their eggs to keep them cool, and eggs without that protection would have baked to death in the hot summer sun, Haffenden said.

“Immediately, we informed the U.S. Fish & Wildlife Service. … And we told the Alabama Department of Conservation and Natural Resources, which added the area to their patrol route,” Barnes said.

Audubon also surveyed the entire island, finding 520 active least-tern nests and 13 black-skimmer nests.

State officials say the current least-tern colony may be the largest on record for Alabama, Barnes said.

“Even with all the eggs that were lost, this site has still been a huge success for the birds,” she said.