Citizen Scientists Keeping Watch Over Endangered Least Terns In Mission Bay
It's nesting season in Mission Bay.
Endangered birds called least terns have built almost 100 nests in the sand and brush on Mariner's Point. They're right next to boaters and other people in the park, and planes fly constantly overhead, but the birds don't seem to mind.
These are some well-cared-for terns. In late March, volunteers from San Diego Gas and Electric and the San Diego Audubon Society helped clear out their nesting area. Chris Redfern, the executive director of San Diego Audubon, said they removed tall non-native bushes so the least terns can see predators like seagulls and falcons coming.
"They need to see that bird coming so they can all rise up together as a group, they flush up into the air, and then they mob that predator by dive bombing it, pooping on it, to drive it away from the site," he explained.
The least terns are tiny — about 9 inches long and just under a tenth of a pound. They migrate 3,000 miles from South America to nest in San Diego and along California's coast. If they think a nesting site has too many tall bushes, they'll turn up their beaks at it. The problem is, then they might not nest at all.
After Mariner's Point was made just the way the terns like it, about 100 birds arrived in late April and settled in. They built nests, laid eggs and a few weeks later, chicks that look like little grey puff balls hatched. But least-tern care didn't stop there.
San Diego Audubon Society has recruited citizen scientists who've spent hours observing four least tern nesting sites in Mission Bay. This year is the first that some of this monitoring has been done by volunteers. Mother and daughter Padma Jagannathan and Sree Kandhadai have been out every weekend since nesting season began in May to look for predators.
"We've seen a couple of osprey," Jagannathan said.
"We've seen lots of gulls," Kandhadai added.
"And we've seen gulls, but nothing like a raptor or a falcon," Jagannathan said.
When they see a predator, which can also include rats, coyotes, feral cats and raccoons, they write it down. If the predator is hurting the terns or stealing their eggs, they can call the state's wildlife services department and ask them to remove it. But Rebecca Schwartz, Audubon's conservation program manager, said this can get tricky when the predator itself is endangered.
"With the peregrine falcon, they were only recently de-listed from the endangered species list, but they're still a fully protected species in the state of California," she said. "So it becomes a really complicated situation when you have one threatened species predating an endangered species, it's not a simple solution."
Audubon volunteers need to provide proof the falcon is a tern-hurting repeat offender. Then the falcon can be trapped and taken all the way to the Oregon border.
All of this effort to protect the least tern might seem like it goes against nature taking its course. But Schwartz sees it differently.
"In a natural system they would be totally fine," she said. "Before people were here, people in cars, and dogs, and cats and urban predators, the terns were doing great. They could even sustain a high level of predation. But because our beaches are so heavily utilized, and because their nesting is so highly restricted to these tiny little islands that we set aside for them, it makes them so vulnerable."
No one can go into the fenced-off park on Mariner's Point; it's reserved for the terns. So during nesting season, which runs through mid-September, volunteer tern watchers sit on a bluff just outside, looking at terns through binoculars. Bill Whiteside has been out at 6 a.m. almost every day watching the terns, but he says he doesn't get bored.
"I can get bored somewhere else," he said. "It's fun just being able to watch the birds and just kind of quiet your mind and it's a beautiful setting."
Whiteside and the other volunteers are also in on the secret. Many who visit Mission Bay to boat, run, or lie in the sand likely don't know that just a few yards away, an endangered species is struggling to make a comeback.