It's not the kind of early-bird weekend crowd you'd expect to see crashing the gates of the Naval Weapons Support Facility in Seal Beach. But here we are, about 40 latte-sipping civilians and me chatting beside a barbed wire fence with binoculars slung around our necks.

We're gathered in a parking lot on the most uninviting-looking block of Seal Beach Boulevard, between the ocean and Interstate 405. Up the road is a Boeing plant. Across the street, a pair of oil derricks nods monotonously. Twenty feet away hangs a sign: "Keep Out -- Authorized Personnel Only." That's no idle threat beside this manned military gate.

An anomalous blue-and-white van airbrushed with flying pelicans on the hood and doors exits the base and stops in front of the crowd, ready for another load of people. Folks in shorts and running shoes board the van, which turns around and scoots past security and back onto the base without a hitch.

On any other morning, this quirky civilian invasion at the Seal Beach Naval Weapons Station would simply not fly. But on the last Saturday of each month, the gates briefly open to the public for a two-hour tour of the property's alter-ego: the Seal Beach National Wildlife Refuge, one of the most reclusive wildlife sanctuaries and endangered bird habitats in the country.

It occupies about a fifth of the 5,000-acre weapons station, which has been here since World War II. The refuge was established nearly 40 years ago to protect the California least tern and the light-footed clapper rail, two of the state's most-threatened avian subspecies.

Peregrine falcons, brown pelicans and the Belding's savannah sparrow -- also threatened -- call this tidal salt marsh in the Anaheim Bay estuary home. So do coyotes, striped shore crabs, hundreds of thousands of migratory birds along the Pacific Flyway and the odd visiting leopard shark and sea turtle cutting in for a bite from the ocean.

The pelican van deposits the final load of passengers in front of the refuge's Nature Center, a small, un-Navy-ish building muralized with birds and butterflies, overlooking a giant marsh with an empty road and a line of electrical poles running through the center of it.

"How many folks here have been to a National Wildlife Refuge before?" asks Chantel Jimenez, a U.S. Fish & Wildlife employee who is co-hosting today's tour with khaki-vested volunteers from the Friends of Seal Beach National Wildlife Refuge.

Some hands go up. Plenty don't.

"I didn't even know this place existed until a few weeks ago," mutters a voice in the crowd. "And I've been living here for over 10 years."

It's one introverted wildlife refuge. And camera shy. No photography is permitted on the base for security reasons.

The two-hour tour begins inside the Nature Center, a single room furnished with displays of native bird specimens, a clapper rail nest, rows of plastic chairs and a TV monitor. During a 20-minute narrated slide-and-video presentation, our group is brought up to speed on some inconvenient truths -- 97% of Southern California's original coastal wetlands have been eradicated by urban development.

After the show, volunteers lead guests into a native plant garden behind the building and along a circuitous path lined with red and orange monkey flowers, coyote brush, sycamores, cherry bushes, flowering poppy plants and enough bunnies hopping around to further disguise the fact that one of the largest ammo dumps on the West Coast is sharing this gated property.

"It would be wall-to-wall Mediterranean condos if the base wasn't here," says Gregg Smith, a Naval public affairs officer chaperoning the tour.

He mentions that these wetlands were in the cross hairs of a proposed highway project in the late 1960s that the Navy, the Sierra Club and several other groups worked together to overturn. The Navy and the Sierra Club working together -- that alone is worth repeating.

"Yeah, there were definitely some strange bedfellows fighting to get this land protected as a refuge," Smith says. "But I think the end result has been extremely beneficial across the board."

Finally, it's time to head out along the marsh -- and maybe snag a rare glimpse of a least tern or one of the 60 resident light-footed clapper rails of just 800 in existence.

We walk along a gravel path beside a flat, empty road flanked by wet fields of cord grass and pickleweed toward a wooden observation deck on the edge of the marsh about half a mile away. At a glance, it's looking pretty vacant today -- barren even -- for a wildlife refuge. The real bird traffic will arrive during its migrational peak in the late fall and winter. But even now, if you slow down and open your eyes, things show up.

Overhead, a red-tailed hawk soars into view, in an aerial dogfight with a pair of outraged crows. Swallows swoop in and out of the frame. An egret gently lands and pecks at the earth. A striped-shore crab lumbers out of the mud. A tiny skeleton shrimp scurries around in a dish at a microscope station set up along the trail.

Then a rail and a tern suddenly appear -- right on the observation deck.

OK, so they're mounted specimens. But the live ones are out here too -- somewhere.

"The rail is a year-round resident, but it's one of the most secretive birds in the refuge," says Kristen Bender, a docent on the tour and the president of the Friends of Seal Beach group. "The least tern breeds during the summer in a special fenced-off area right over there," she adds, pointing to a clump of land in the center of the marsh called NASA Island, where some of the Saturn project rocket boosters were built and tested in the 1960s. "We call it Tern Island now," Bender says. "You might be able to see or at least hear some of them out there fishing today."

I don't. Not today. Not this month. But on a peaceful Saturday morning on a Naval Weapons Station, it's comforting to know that a former rocket booster site has been taken over by terns.

travel@latimes.com