Good Fences Make Good Neighbors: When Survival Depends On Keeping Predators Out

By Lisa Cox

Seal Beach National Wildlife Refuge staff and volunteers recently rebuilt a six-foot fence to help protect nesting and juvenile California least terns from ground predators. “Without the fence we probably wouldn’t have any tern productivity, and all the eggs or chicks would likely be eaten by either ground or avian predators,” said refuge manager Kirk Gilligan.  Credit: John Fitch/USFWS

It’s not easy being a tern in southern California.

Due to habitat loss from development and human use of beaches during nesting season, endangered California least terns are left nesting in small areas, making them highly vulnerable to predators. At the U.S. Fish and Wildlife Service’s Seal Beach National Wildlife Refuge, south of Los Angeles, Calif., staff and volunteers recently rebuilt a six-foot chain-link and electrified fence to help protect the birds from ground predators.

Tern colony nesting area on Seal Beach National Wildlife
Refuge. Credit: USFWS

The terns nest on a three-acre manmade island on the refuge, which is situated within the Seal Beach Naval Weapons Station. This particular area was historically used for detonation activities and testing fire-fighting foams, however it is now a safe place for the birds.

The Seal Beach National Wildlife Refuge was established in 1972, with one of its purposes being a nesting site for federally endangered birds. The least terns, once found all along the sandy beaches of southern California, were listed as endangered in 1970.

And, while the terns have been nesting on this tiny area of the refuge since 1979, they face continued challenges. Red foxes, skunks, opossums, raccoons, feral cats and coyotes seek tern eggs and chicks for food.

Refuge maintenance worker Justin Solberg, biologist Rick Nye and refuge volunteer Mark Walsh install fencing around the tern nesting area on Seal Beach National Wildlife Refuge recently. Credit: Kirk Gilligan/USFWS

“Because we’ve had such an extensive loss of their natural undisturbed beach nesting habitat, humans must step in to ensure the species does not go extinct,” says Kirk Gilligan, refuge manager. “Without the fence we probably wouldn’t have any tern productivity, and all the eggs or chicks would likely be eaten by either ground or avian predators.”

Avian predators include owls, hawks and falcons. When refuge biologists document these birds preying on terns, they attempt to trap and relocate the predators. Terns are also susceptible to dying from cold, wet weather, extreme heat, starvation, dehydration and unusually high surf or tides.

California least tern chicks hatch on NASA Island in 2007. Credit: John Fitch/USFWS

Yet, there is hope for the California least tern.

“The success of the California least tern program on the refuge really depends on a strong working relationship between refuge staff and the Seal Beach Naval Weapons Station environmental staff since both contribute funds and manpower in a partnership to make sure the terns are monitored and protected here,” Gilligan says.

Predator threats are real, as evidenced by the many coyote
tracks outside thefence. Credit: Kirk Gilligan/USFWS

Bob Schallman, a U.S. Navy Biologist with the Seal Beach Naval Weapons Station, has been helping monitor these terns for the past twenty years.

“Overall, tern fledgling success has fluctuated over the past three decades, but it is has kept fairly steady in recent years,” he says. “In the late 70s there was zero, in the 80s the numbers started to increase, and by 1993, just over 360 chicks had fledged. This year, in 2016 we successfully fledged 35 terns.”

You can help the California least tern. The summer breeding season is the most fragile time for the birds. Throughout the beaches in southern California, please respect signs, ropes and wire fencing indicating a nesting area for either California least terns or Western snowy plovers. Do not fly kites or balloons near these areas. They may look like avian predators to the birds and cause them to leave their nests.

Make sure your dog is leashed and far away from the area. If the chicks are able to fledge and fly away, you and your family can witness an endangered species raising its family.

Take care of your beach and you’ll be taking care of a larger connected, coastal ecosystem we all share.

A recently hatched California least tern chick, flightless and vulnerable, runs along the beach on the refuge. Credit: Kirk Gilligan/USFWS

About the Refuge:

The Seal Beach National Wildlife Refuge is managed by the U.S. Fish and Wildlife Service in collaboration with the Department of the Navy, and serves as a critical habitat and winter stopover for many birds along the Pacific flyway.

The refuge is located within Naval Weapons Station Seal Beach. Public access in the refuge is limited or restricted to once-a-month tour (last Saturday of each month) since it is located within an active military base.

The 965-acre refuge is located in Orange County, Calif., and encompasses remnant saltwater marsh in the Anaheim Bay estuary.

The refuge also serves as an island of habitat in the midst of a dense urban setting for a wide variety of fish, wildlife and plants. Wildlife ranges from peregrine falcons and ospreys to grey smooth-hound sharks, round stingrays and green sea turtles, monarch and painted lady butterflies to microscopic aquatic invertebrates.

An adult California least tern soars over Seal Beach National Wildlife Refuge. Credit: Rinus Baak/USFWS

Lisa Cox is a visitor services and public affairs specialist for the Service's San Diego National Wildlife Refuge Complex.