CHARLESTOWN, R.I. – The tiny Atlantic piping plover, a federally protected bird, has given beach-goers headaches for decades.

The species breeds on East Coast beaches during warm weather, which means entire stretches of shoreline can be put off-limits just as people want to enjoy the coast.

But today, two decades after the plover was declared a threatened species, biologists are crediting the beach closures, twine barriers and other buffers between birds and humans for a 141 percent increase in the Atlantic piping plover population.

“Those birds have been earned the hard way,” said Anne Hecht, who supervises the recovery effort for the U.S. Fish and Wildlife Service.

The brown-and-white birds breed in tenuous dents of sand just above the high-tide line, where their nests can be flooded by storms, targeted by predators and easily damaged by humans.

Once a fixture on the East Coast, the fist-sized piping plovers lingered as human development pushed them from their beachfront breeding grounds, especially in the seaside building frenzy after World War II.

Man-made threats were just half the problem. Susi von Oettingen, a federal endangered species biologist in Concord, N.H., paused for breath while reciting a long list of plover predators as large as coyotes and small as ants.

Sometimes drawn to the beach by human trash, those predators will find and eat plover nests and chicks. Ants swarm the eggs and eat them.

The birds’ numbers dropped to just 722 mating pairs in 1985, prompting federal officials to require that property owners protect the birds. They also began issuing recommendations that interfered with humans’ beach life.

At a minimum, the U.S. Fish and Wildlife Service wanted property owners to put up signs and fences marking a 50-foot barrier between people and plovers. Since dogs chase plovers, they had to be kept on a leash or kept off the beach altogether.

Beach buggy enthusiasts probably were hit the hardest. Their off-road vehicles are banned from many plover beaches during nesting season because one stray tire can smoosh an entire brood.

The bans outraged beach-goers.

“It was awful,” said von Oettingen, who remembers when the National Park Service closed its Cape Cod beaches to off-road vehicles. “They had death threats. … They had parades of vehicles in the streets shouting it was not going to happen.”

The backlash united unlikely groups of beach users. While anglers protested the beach buggy restrictions, nudists in Rhode Island sued the federal government for severely curtailing access to their favorite beach.

In the end, a federal judge decided that nude sunbathing was not a constitutionally protected right.

Federal officials have since warned cat shelters not to release neutered felines near plover beaches, and the nests forced the cancellation of a fireworks display in Ogunquit, Maine. Even now, federal agents investigate cases of suspected vandalism against plovers.

Partisans on both sides say tempers have cooled since the battles of the 1980s and 1990s.

George Cairns, president of the Massachusetts Beach Buggy Association, said the era of protest is over. He now describes his organization as a conservation group that wants the piping plovers to recover.

Since the population is growing, Cairns said it is time to rebalance the rules.

Rather than banning buggies, he proposes using a volunteer warden to wave buggies away from plover nests and sand-colored chicks. He’s looking for a town willing to give the idea a trial run.

“People are part of the environment, too,” he said.