San Diego is a biodiversity hotspot with hundreds of bird species, including the California least tern, migrating through the county each year. Located along what’s known as the Pacific Flyway, migrating birds often rely on Mission Bay to feed and rest. Over the years, however, Mission Bay has been highly modified—once boasting 4,000 acres of wetland as well as associated dunes, today less than 5% of this habitat remains.
Chris Redfern, Executive Director of the San Diego Audubon Society, explains “In a natural environment, wetlands and dune systems act as protective barriers against coastal erosion and sea level rise.”
The San Diego Audubon Society hopes to reverse this trend with their habitat restoration program. In particular, they currently manage four least tern nesting sites, including Mariner’s Point, FAA Island and two sites on Fiesta Island—Stony Point and North Fiesta. The most productive colony for least terns is Mariner’s Point, located next to Bonita Cove, where an average of 150 breeding pairs come to nest each season.
Redfern says, “The least tern is a bird that has inhabited this area for thousands of years. In the last hundred years, in the blink of an eye, the habitat they were using along the coast basically got developed by people.”
The San Diego Audubon Society has been helping to maintain Mariner’s Point for almost three decades by hosting volunteer restoration programs. Their annual least tern habitat restoration event with San Diego Gas & Electric employees is their most well-attended.
On a balmy winter morning in February, Redfern shows volunteers how to distinguish between invasive weeds like fillaree and devil’s thorn as opposed to the beach evening primrose, a native plant that least tern chicks use for shade and to hide from predators. SDG&E has partnered with the San Diego Audubon Society for the last seven years to bring more than 100 employees, their families and friends to help clear vegetation from this fragile habitat.
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By mid-April the California least terns will arrive at Mariner’s Point and stay throughout the summer. The males will dive head-first into the bay to catch anchovies or top smelt. They will return to the sandy point, offering the fish to a female while performing a courting dance. The females will then lay their eggs in a nest.
Megan Flaherty, the Audubon Society’s Restoration Program Manager, explains, “Removing tall vegetation is important because the least terns are small and low to the ground—nine inches from beak to tail feather when full grown. If there’s a really tall bush in front of them, they can’t see a predator coming. That reduces their ability to defend their chicks.”
The predators of least terns are normally birds of prey such as the red-tailed hawks and peregrine falcons. Due to urbanization, however, new predators have included crows, ravens and seagulls. “Without predator control it’s possible for an entire colony of chicks to be wiped out for that nesting season,” Flaherty says.
It’s thanks to volunteers who pull invasive weeds from Mariner’s point that the least terns will have a safe summer home. Flaherty adds, “This site is a really good example of how continued restoration can result in almost completely native plant communities.”
With the help of volunteers and community members, Redfern and his team at the San Diego Audubon Society have an ambitious vision. Building off their restoration programs, they are working on a project called ReWild Mission Bay, which aims to restore a portion of Mission Bay’s historic wetlands.
In addition to habitat restoration, SDG&E has provided Environmental Champions grants to the San Diego Audubon Society for their Outdoor Explore! Program, which has been delivered to over 45 different schools and takes students on guided hikes through canyons located in their very own neighborhoods.
The San Diego Audubon Society has existed for over 60 years and currently has about 2,000 members who engage in habitat restoration and educational programs. To bring more conservation awareness to the public, the nonprofit operates the 785-acre Silverwood Wildlife Sanctuary and the Anstine Audubon Nature Preserve.
“Our whole vision and strategy for success is to create a culture of conservation in San Diego where people actively engage in enhancing and protecting habitat and species,” Redfern says. “We want people to come out and actively do what these SDG&E employees are doing.”