A Drone Crash Caused Thousands of Elegant Terns to Abandon Their Nests

California wildlife managers are hoping the birds relocated to other nesting sites. Meanwhile, they are working to ensure this doesn't happen again.

On the morning of May 13, Peter Knapp stepped onto an ominously quiet California beach. The night before, he’d noted a horde of boisterous Elegant Terns just starting to incubate their eggs in the Bolsa Chica Ecological Reserve, 30 miles south of Los Angeles. But the roughly 3,000 birds were missing. 

“I didn’t see the terns anywhere on the reserve,” says Knapp, a seasoned wildlife monitor with the California Department of Fish and Wildlife. “So I started looking around.”

By the time he reached North Tern Island, the birds' nesting site, he’d found an answer. On the ground was an illegal drone, which had obviously crashed. The birds did not return, abandoning some 1,500 sand nests, each holding one or two eggs. 

“It was devastating. There was no other word,” says Melissa Loebl, the reserve manager at Bolsa Chica.

Bolsa Chica Ecological Reserve is one of only four known Elegant Tern nesting sites in existence. The other three are located on Isla Rasa in the Gulf of California, San Diego Bay, and Los Angeles Harbor. That narrow range makes the loss of one nesting site all the more gut-wrenching. But this undeniable tragedy may not have spelled doom for this generation of Elegant Terns.

Both the crash and its aftermath have prompted a deep, wide-ranging discussion about everything from conservation to public education to drone law. In an email statement about the crash, the Federal Aviation Administration (FAA) indicated that it “is aware of and is investigating the incident.” The agency is now working alongside the California Department of Fish and Wildlife and Bolsa Chica Ecological Reserve to develop clearer guidelines around sensitive wildlife areas, Loebl says. 

Over the last year, the number of visitors to the reserve doubled, driven by the public’s desire for COVID-safe activities. While guests are always welcome, Loebl says that certain aspects of increased traffic have been disruptive for the 300 bird species that call Bolsa Chica home. Sometimes visitors come with noisy electric bikes or dogs, both of which can scare away wildlife. And then there are the drones, which look like predators to some birds.

Recreational drone pilots are required to register their craft with the FAA. Even then, they aren’t free to fly about willy-nilly. Airspace around tall buildings and airports, for example, is strictly controlled. Wildlife areas, like state and national parks, are usually off-limits as well. The FAA provides maps of these spaces so that commercial and recreational pilots alike can determine where they are and aren’t allowed to fly. 

Unfortunately, the maps aren’t always accurate. If you look up Bolsa Chica Ecological Reserve on B4UFLY, the FAA’s drone-centric mobile app, it appears to be open airspace, even though it is technically protected as a U.S. Fish and Wildlife Service area. Some Bolsa Chica volunteers suspect that the drone belonged to a recreational pilot who didn’t know better. The perpetrator has yet to be identified.

Unlike scrappier seabirds, Elegant Terns are especially sensitive to disruption during nesting season thanks to a couple of unique behaviors. First is flock density. “Their one big anti-predator defense is to nest in these huge numbers,” says Kate Goodenough, a seabird ecologist at the University of Oklahoma. Every year, thousands of sleek, black-and-white Elegant Terns lay eggs along the beaches of small islands. Like New York City apartment tenants, they make the most of the available real estate, squeezing up to 15 nests in three square feet of sand. 

The second behavior is known as group adherence. Unlike many bird species, an Elegant Tern’s loyalty lies with the flock rather than the breeding ground itself. “If some individuals take off for whatever reason,” Goodenough says, “the majority of the group also takes off and leaves.”

Prior to the late 1950s, Elegant Terns bred almost exclusively on the 135-acre Isla Rasa in the Gulf of California. Over the last 60 years, however, the orange-beaked birds have made their way up the California coast, following the anchovies that comprise most of their diet. While the anchovy schools were initially pushed out by overfishing, a combination of factors continue to drive them northward. 

“With global warming, the Gulf of California is getting higher temperatures, which means less food for the birds,” says Enriqueta Velarde, a seabird ecologist at Universidad Veracruzana, “so they’re tending to move.” The San Diego Bay site was discovered by biologists in 1959, followed by Bolsa Chica in 1987 and LA Harbor in 1998.

Around 180,000 Elegant Terns (or 90,000 breeding pairs) exist worldwide—enough to keep them off the endangered species list. But many experts recommend that these birds receive strong protection due to their extremely limited breeding range. 

Despite the loss, the Bolsa Chica terns may still have a chance to nest this summer. Their mass evacuation happened fairly early in their breeding season in Southern California, according to Velarde. It’s possible that some of the terns relocated to the San Diego Bay nesting site, about 100 miles south. 

Brian Collins, manager of the San Diego Bay National Wildlife Refuge, says that around 14,750 new breeding pairs have established nests in the area since May 26, in addition to the 4,850 already nesting at the site. While he can’t say for sure whether the new terns came from Bolsa Chica, he confirmed that it is very possible.

It’s also feasible that some displaced terns traveled north to the Los Angeles Harbor nesting grounds. And there is a third option: “The other possibility is that there are some other Elegant Tern nesting sites that we don’t know about,” Velarde says.

Now that they’ve been scared away, it's not known whether the terns will return to Bolsa Chica in the future. To increase the chances, workers at the ecological reserve are doing everything they can to protect the nesting site. In addition to restricting airspace and adding signage, they’re partnering with three local nonprofits—the Bolsa Chica Conservancy, Bolsa Chica Land Trust, and Amigos de Bolsa Chica—to develop a land stewardship program. “It’s good to see the outpouring of support from our community,” Loebl says.