California least tern’s survival in Mission Bay depends on volunteers

Samantha Hughes, Kaylee Cole, Karina Ornelas, Maren Appert and Hillary Rivas at a habitat restoration project.
Samantha Hughes, Kaylee Cole, Karina Ornelas, Maren Appert and Hillary Rivas at a habitat restoration project on March 19 at Mariner’s Point in Mission Bay.
(Sandeep C. Dhar)

The San Diego Audubon Society, a chapter of the National Audubon Society, is helping to restore nesting sites for a species of endangered bird in Mission Bay.

The California least tern, recognized both federally and by the state of California as an endangered species, produces a majority of its fledglings in the Mission Bay area.

For the record:

3:36 p.m. April 6, 2022Corrected the first name of Maren Appert in the article.

Maren Appert, conservation coordinator with the San Diego Audubon Society who studies environmental science at SDSU, said having volunteers come out to help with the local restoration efforts is invaluable to the species’ success.

“It creates the most successful habitat with the more people we get out there,” Appert said. “The species wouldn’t be able to persist without volunteers.”

Over 60 percent of the species’ nesting sites are located in San Diego, with nesting most concentrated in Mission Bay. The San Diego chapter of the Audubon Society maintains the four most productive nesting sites in Mission Bay at Federal Aviation Administration (FAA) Island, Mariner’s Point, Stony Point and a northern portion of Fiesta Island.

A California least tern feeding its chick.
(Paul Tessier /

Appert said the California least tern is an important ecological link with which to measure the health of the local ecosystem and food web. In years where there are higher chick mortality rates, this can be an indication of issues with food availability, which often coincides with ocean temperatures relating to climate change.

The terns are also a source of prey for local predators, playing a role in the vitality of peregrine falcons, gulls, blue herons and crows.

The species also contributes to the local ecosystem by moving nutrients toward the coastal habitat. Especially in sand dunes that are lacking in nutrient levels, they contribute toward the support of local vegetation. Although the dunes in Mission Bay are mostly man-made land structures produced by dredging, the seasonal migration and feeding patterns of the terns still play a crucial role in nutrient redistribution.

The tern population is on the decline

The California least tern was one of the first species protected by the Endangered Species Act of 1973. Around that time, there were only 200 nesting sites counted for the coastal bird. Conservation efforts over the past few decades revitalized the species’ population from a dismal population of roughly 600 nesting pairs.

Their recovery peaked in 2009, when nesting pairs were estimated between 7,100 and 7,350, producing as many as 2,000 fledglings. This population has since seen a dramatic downward trend, culminating in a 2021 estimation of nesting pairs in the range of 3,500 to 4,300, producing as few as 800 fledglings.

With regards to nesting trends in Mission Bay, the Audubon Society estimates around 91 fledglings were produced last season. Most of these fledglings were hatched at the Mariner’s Point and FAA Island nesting sites, with none being produced at Stony Point or North Fiesta Island.

Kaylee Cole of the San Diego Audubon Society doing restoration work at FAA Island on March 20.
(Tyler Faurot)

A number of factors have been postulated as to why the population is declining. Increased pressure from local predators and a continued habitat degradation and fragmentation have been recognized as possible impacts.

“It could also be the rising ocean temperature, which would push sardines out deeper into the water column,” Appert said. “Sardines are their number one source of food, so if they can’t access their food you can imagine their success rate won’t be as high.”

It took many volunteers to move the plants removed during a March 19 habitat restoration project on Mariner’s Point.
It took many volunteers to move the Beach Evening Primrose removed during a March 19 habitat restoration project on Mariner’s Point in Mission Bay.
(Sandeep C. Dhar)

Megan Flaherty, conservation manager at the Audubon Society, also stressed human disturbance, including local watersports in Mission Bay disrupting optimal nesting habits.

“I think people are unaware of the impact they have on this species,” Flaherty said at a March 20 restoration event, “when they rev their engines too loud or drive too erratically near these sites, it can seriously impact their nesting habits.”

Flaherty also said she hopes people will respect the restrictions for human access to FAA Island, as trespassing can seriously impact the nests that are established there.

Volunteers make a difference

Prior to having to cancel their volunteer events due to the COVID-19 pandemic, the Audubon boasted as much as 1,000 volunteers per year, with an estimated 750 volunteer hours worked by local students.

“During that time where we had no volunteers due to COVID we had a pretty paired-down crew,” Appert said. “Managing those sites with only about seven paid staff members is a little tricky.”

Scattered shells at a nesting site on FAA Island help hide California least tern eggs from predators.
(Tyler Faurot)

The terns nest in open sand, relying on camouflage to protect their chicks from predators. Invasive vegetation like weeds can encroach on nesting sites and discourage the birds from building nests.

Appert said that having more volunteers participate in restoration events where they remove vegetation from nesting sites by hand allows for a minimal impact on the soil. While working with a limited staff during the pandemic, the Audubon Society instead would scrape out vegetation with heavy machinery to make up for its workload. This results in a more disrupted soil and packed earth, culminating in nesting conditions that are less than optimal for the least tern.

Habitat restoration can be a family activity.
(Sandeep C. Dhar)

The Audubon group is now back at full capacity to take volunteers along with them. At its restoration event on March 20 there was upwards of 20 volunteers who removed around 800 pounds of invasive vegetation, according to Flaherty. Their efforts provided more open soil for the birds to nest within the coming months. In another recent event, Audubon hosted as many as 80 volunteers.

“We are so grateful to have people come out again this year,” Appert said. “It’s made such a difference on the sites as compared to the last few years.”

The San Diego Audubon Society hosts ongoing events throughout the season, listed on its website calendar at

It is currently taking applications for the Conservation Team Leader program through May 2 for any interested community members to be more involved with Audubon’s efforts. For details, go to

Volunteers thinned the Beach Evening Primrose, a native plant, because California least tern needs 80 percent open sand.
Volunteers thinned the Beach Evening Primrose, a native plant, because California least tern needs 80 percent open sand to nest on. The primrose will grow back in abundance in the fall.
(Sandeep C. Dhar)

Want to volunteer?

Several restoration and cleanup events sponsored by various organizations are held in the area. Here are some options:

San Diego Audubon Society: California least tern habitat restoration

Upcoming events: 9:30 a.m. to 12:30 p.m. Wednesday, April 6 and Sunday, April 10.

Location: Mariner’s Point, 3300 Mariner’s Way (Mission Bay).

Tasks: Remove invasive weeds to make room for nesting endangered birds.

Details: All supplies provided, including tools, gloves, water and snacks. Wear closed-toe shoes and bring a reusable water bottle and hat.

Contact: Maren Appert at

* * * * *

Friends of Rose Creek: Native Plant Work Party

Upcoming events: 9 to 11 a.m. Saturday, April 9; May 14; June 11 and July 9.

Location: behind Rose Creek Cottage, 2525 Garnet Ave. (Pacific Beach). Park on Fogg Street, just south of Garnet Avenue.

Tasks: Weed, water, remove invasive non-native plants and trash, and during the fall and winter plant native species.

Details: Project happens monthly on the second Saturday on The Nature School’s native plant interpretive garden behind Rose Creek Cottage. Bring water and heavy-duty work or gardening gloves. All ages welcome, including children.

Contact: Kain Zirk at

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Friends of Mission Bay Marshes: Work Party at Kendall-Frost

Upcoming events: 9 to 11 a.m. Saturday, April 16; May 21; June 18 and July 16.

Location: Kendall-Frost Marsh, 2055 Pacific Beach Dr. (Mission Bay).

Tasks: Remove non-native plants, plant and maintain native plants, remove trash and work on other needs, such as fencing and irrigation.

Details: Wear long pants, long-sleeved shirts, closed shoes and a hat. Bring water bottle, gloves and gardening tools if you have them. All ages welcome, including children.

Contact: RSVP with Isabelle Kay, reserve manager, at

Good to know: Kay said the reserve’s 16 acres are part of a 40-acre wetlands area owned between the University of California Native Reserve System and City of San Diego. It is an area crucial for Ridgway’s rail, Belding’s Savannah sparrow and California least tern, which are all endangered species.

Kay said Ridgway’s rail and Belding’s Savannah sparrow live there year-round and it is the hunting ground for the California least tern.

Among those working on a habitat restoration project were Hillary Rivas, Megan Flaherty, Kaylee Cole and Karina Ornelas.
Among those working on a March 19 habitat restoration project on Mariner’s Point in Mission Bay were Hillary Rivas, Megan Flaherty, Kaylee Cole and Karina Ornelas.
(Sandeep C. Dhar)