Robins are recurrent, cowbirds copious, and starlings are simply superfluous. But bluebirds? If you're under 30 and live in suburb or city east of the Rockies, according to the North American Bluebird Society, you are unlikely to have seen one at all.

So when a longtime Alexandria bird watcher, retired Lt. Gen. Arthur S. Collins Jr., 66, and his neighbor, William C. Bryant, 64, set out with birdhouse blueprints and binoculars to lure bluebirds to the lawns of the Virginia Theological Seminary in Alexandria this April, they did so with guarded optimism.

"We knew it was a long shot, but I'd seen one for the first time in my life about a year ago south of Warrenton , and I thought it was the most beautiful thing I'd ever seen," said Collins. "I thought, wouldn't it be wonderful if I could bring one back here?"

Life hasn't been all seed and song for the blue-backed, peach-breasted Eastern Bluebird. In the past 50 years, their numbers have diminished by an estimated 90 percent, and for 10 years they've been on the National Audubon Society's list of threatened American birds. Development has felled their nesting areas, and they've been outfought and outfoxed by the starling and English sparrow, who peck at their heads and plunder their nests.

Three weeks ago, however, the unlikely happened in Alexandria. One of Collins' and Bryant's carefully constructed gray boxes yielded a brood of four baby bluebirds. "My goodness, I was excited! " Collins said. "I went up there and looked in the box and there were four little eggs. Well, it was a great thrill. I closed the box and rushed home to check my bird books."

"I was less optimistic than Art," said Bryant, a retired journalist. "But he's a good friend and neighbor, and when he suggested it, I went along . . . Now I'm quite optimistic, we've got a family of six around here."

The North American Bluebird Society, a 4,000-member organization based in Silver Spring that keeps track of these things, confirmed the sighting, and declared it the first successful bluebird nesting inside the Capital Beltway in at least a decade. Prince George's County made the bluebird its county bird in 1976, but according to bluebird society Executive Director Mary D. Janetatos, a nest or two reported there this spring failed to yield any fledglings.

"I don't know of any bluebird nesting this close in since way back in the '50s," said veteran Mount Vernon birder Jack Abbott, who with his two sons is one of a hard core of about 50 dedicated Northern Virginia amateur ornithologists.

"Bluebird nests inside the beltway are very rare, very hard to find," agreed Lawrence Zeleny, a retired chemist and a bluebird aficionado who writes about bluebirds for the local Audubon Naturalist Society.

Collins' and Bryant's first batch of bluebirds left the nest recently, but because the female frequently returns to lay more eggs, a bluebird watch is on.

"I come up here every day or two," said Collins one recent afternoon, staring balefully at the wrens who had taken over one of his boxes. Like some of the other members of the bluebird society (Its motto: "Where Have All the Bluebirds Gone?") who build special birdhouses from all kinds of material, from wood to empty Clorox bottles, eternal vigilance is the price willingly paid for bluebird happiness. The wrens will be allowed to stay, Collins decided, but sparrows and starlings will be cast out.

In the hierarchy of bird lovers, "birders" are to ordinary bird watchers as gourmet chefs are to cooks. Birders often keep lifetime lists of bird sightings, and some have been known to spend small fortunes traveling around the world for glimpses of a rare species. Collins describes himself as a bird watcher. "There are a lot of us out there who aren't real experts," Collins said. "But we're dedicated."

And the triumphs are just as keen. "I've lived a long time and I can't think of another thing that's given me more excitement or satisfaction," said Collins. "It's been a thrill, I can't tell you!"