On a nesting island at the Bolsa Chica Ecological Reserve in Southern California, thousands of elegant-tern eggs dot the sands, abandoned. Now it appears the eggs will never hatch.

After a drone crashed on the reserve grounds on May 13, about 3,000 adult elegant terns were scared off, leaving about 1,500-2,000 eggs behind.

“It was devastating,” Melissa Loebl, an environmental scientist who manages the reserve, told The Washington Post. “That’s one of the largest losses we’ve had.”

Drones, which California Fish and Wildlife officials say are prohibited on state reserves, can look like a “giant bird, a giant predator,” to the elegant terns, said Michael Horn, a professor emeritus of biology at California State University at Fullerton.

“That’s going to cause them to abandon,” Horn told The Post.

The elegant tern is one of more than 800 species of plants, animals and fish that rely on the reserve as a habitat. Located in Huntington Beach, Calif., Bolsa Chica is about 1,300 acres with habitats that include open water, coastal dunes, salt and freshwater marshes, and seabird nesting islands.

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Before the drone crash, Loebl said the reserve had seen an increase in visits. She estimates attendance has doubled in the past year, as more people sought outdoor activities during the pandemic, a shift that’s pushed reserve officials to think about how to “accommodate that many people without harming the wildlife.”

There’s also been an increase in dogs roaming off-leash, which Loebl said can scare birds. Loebl said dogs, horses and bicycles are all prohibited in the reserve because they can damage the wildlife.

The elegant tern, with its pointy wings and long, orange bill, normally arrives at the reserve’s grounds in April or May for the beginning of its reproductive cycle, said Horn. After the birds mate, they build a nest in the sand, and the females usually lay one egg, sometimes two. After the egg hatches, it can take weeks before the young chick is ready to fly away with its parents, Horn said.

“The eggs should be hatching right about now,” Loebl said. But the eggs are no longer viable.

Roger Lederer, a professor emeritus of biological sciences for California State University at Chico, said birds “don’t abandon their nests very easily.”

In an email to The Post, he noted the recent disruptive activity reported at the reserve, including the off-leash dogs and cyclists, “so I suspect there has been continual stress put on the bird colony and the drone crash was the last straw.”

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The elegant tern is not considered threatened or endangered, with about 100,000 to 150,000 in the population worldwide. But Horn said the birds have limited locations where they breed – three nesting sites in Southern California, including the Bolsa Chica Ecological Reserve, and one in the Gulf of California in Mexico.

“If you lose 1,500 eggs at one site, well, it’s a lot – we’re not diminishing that point,” Horn said.

But he said the elegant tern can live 20 years, which means it can have several reproductive years in its life.

“In the big picture, as long as they nest somewhere else, there’s always next year,” he said.

He said drones could be a “new kind of threat” for the species, in addition to natural predators such as peregrine falcons.

Loebl said the reserve wants to improve its signage reminding visitors about safety regulations, including that drones are not allowed. She said outside groups are looking to help lobby to have the Federal Aviation Administration to list the reserve as restricted airspace.

“These open spaces are a place for wildlife to rest, to breed, to forage and it’s a place where they should feel safe to raise their young and if they truly can’t do that we’re not fulfilling our mission,” she said. “We need to protect these places.”