Getting a bird’s-eye view of the top place to flock

I SEE NOTHING SPECIAL OVER THERE IN the mud and weeds, but apparently a small xylophone factory has just been turned sideways.

Bong, bong, bang, bing, say the weeds.

As these great, goofy tones echo across the wetlands, my hiking companion halts and raises a hand. His name is Philip Unitt, and he wears jeans, sneakers, a droopy mustache and the smile of a man in his element.

“The light-footed clapper rail,” he says in a soft, certain voice.

Bing, bang, bong, bong, say the weeds.

The clapper rail, a.k.a. Rallus longirostris -- dappled, long-beaked and partial to tidal marshes -- is an endangered species with only about 100 pairs in San Diego County. But, of course, Unitt knows where to find them -- the Tijuana River estuary, less than two miles north of the Mexican border.

Unitt, 48, is manager of the San Diego Natural History Museum’s collection of birds and mammals and author of the new San Diego County Bird Atlas. The atlas, published this month by the museum, is the first major effort in 21 years to assess the population of a county that is believed to harbor more bird species than any other in the U.S. So it’s a big book (with a big price: $80), and within its pages lurk two themes.

First: Birders see a different world than the rest of us do. Second: No matter how carefully we compose our snapshots of it, the wild kingdom will never sit still, never quite conform to expectations.

Over the years, 492 bird species have been spotted in San Diego County. And more than 180 of those species have turned up within three miles of where we stand. Scanning the muddy scene with his binoculars, Unitt ticks off some of their names in a flat, yet profoundly interested tone -- like a farmer describing his row crops.

“Hear that?” he says. “That’s the song of the Belding’s savannah sparrow.”

Unitt, who has worked for the museum since 1988, has published more than 30 scientific papers. Like a Wall Street tote board tracking the Standard & Poor’s 500, his head teems with fluctuating data regarding the look, sound, history, habits and distribution of the San Diego County 492.

But ask about his PhD and a bad-boy smile emerges. No PhD. No master’s. He has a bachelor’s degree in zoology from San Diego State. “I’m just a birdwatcher run amok,” he says. “Shhh.”

Now -- as we pad along the shoreline -- listen to what went into writing this tome. Unitt and the museum committed to it in 1996, collecting support from such underwriters as Caltrans and the U.S. Forest Service. The first step was to break the county into a grid with 479 squares and dispatch more than 400 volunteers to the field in nesting and winter seasons.

We’re walking now in square V-10. Within these nine square miles, in the course of 157 observation hours, his troops spotted 183 species.

So here we are: In the nation’s most bird-diverse county, this is the most bird-diverse neighborhood, stretching from the south edge of San Diego Bay, where an old saltworks has long tempted waterfowl with protected ponds, to the Tijuana River Valley, where a freshwater river meanders to the sea.

We work our way north to south. At the Imperial Beach pier, Unitt spots a set of tricolored blackbirds and a surf scoter amid the mussel-encrusted pier pilings. He also spots Oz Osborn, a 79-year-old retired engineer who was one of his most active volunteers on the atlas.

“I don’t know how he kept all those diverse egos going in the same direction,” says Osborn.

From 1997 through 2002, Unitt and company collected sightings and sorted the data, aiming to get it all into print within two years. Things change fast in bird circles. While San Diego County’s human population was increasing by 50% over the last 25 years, its loggerheard shrike population has been plummeting; it’s 10% of what it was in 1984.

The good news is that Unitt’s troops, logging 55,000 hours of observation, made nearly all of their goals. Just one square went unobserved -- a bombing range on Camp Pendleton -- and the troops spotted a dozen previously undetected species, including a gila woodpecker, a magnificent hummingbird and a yellow-bellied flycatcher.

The bad news is that at just about the time the work was done, the county caught fire.

In the last two years, 20% of San Diego County has burned -- about 60 square miles in the Gavilan and Pines fires of 2002 and 602 more square miles in the Roblar, Paradise, Otay and Cedar fires of fall 2003. In other words, the new atlas is a snapshot of a place that no longer exists.

But fire cycles have been around longer than birders have, and the atlas does make a grand starting point for anyone interested in measuring the fires’ effects on bird life. As Unitt notes in the front pages of the book, some species are suffering, but others may flourish -- like Costa’s hummingbirds (which like re-sprouting flowers) and lazuli buntings (which like recovering chaparral ).

Either way, Unitt and company will keep on counting -- they have various post-fire projects well underway -- and the rest of us must stand back in awe of their iron will, their acute eyes and ears, their sheer muddy-booted optimism.

Now we’ve reached the last station in our rounds, the mouth of the Tijuana River, where seven years ago, the greatest surprise of this entire project turned up.

It was a gull, Unitt says, a single Belcher’s gull. That species doesn’t normally get north of Panama, yet one turned up here that August and stayed five months before flapping off.

“Here is this bird in the completely wrong hemisphere,” says Unitt in wonder, “a bird that doesn’t have any migration in this direction at all.”

There’s a photo of it in the atlas: gray and white feathers, yellow beak, orange at the tip. Just another homely gull, I would have thought. But then, I haven’t got the San Diego County 492 atwitter in my head.

To e-mail Christopher Reynolds or to read his previous Wild West columns, go to latimes.com/chrisreynolds.