THE PEOPLE WHO KNEW us were not surprised. Others probably thought we were out of our minds. All we did was drive more than 1,000 miles, bicycle 20, and travel another 50 by boat -- all in just three hectic days -- to see a bird. Not any old bird: a western reef heron.

Look here, I am perfectly normal. I have a good job with the government. It's just that the western reef heron (Egretta gularis) has never before been sighted in the Western Hemisphere. It's usually found only in the tropical coastal regions of West Africa, or in the coastal wetlands between the Red Sea and Sri Lanka. So when it suddenly showed up in Nantucket, Mass., earlier this year, I joined the pilgrimage to catch a glimpse of the bird.

I suppose the reef heron madness that took hold of the bird watching community this summer must seem obsessive to the uninitiated. It probably will only confirm the image that we bird watchers have of being a little eccentric, if not slightly daft. In fact, we are as normal as those who suffer from Redskin fever, or who go slightly crazy about another breed of bird: the Baltimore Oriole.

We are, emphatically, not just a tiny band of elderly folks in tennis shoes. We are people of all ages and descriptions -- as diverse a group, perhaps, as the creatures that fascinate us. What is more, our numbers are growing. We are field researchers, who use birds in their study of biology and behavior. We are conservationists, who are working to preserve habitat and the natural environment. And, finally, we are "listers" -- people whose goal is to compile a growing list of bird species they have seen.

The reef heron mobilized us all. When a once-in-a-lifetime bird appears, it is common for the hard core to jump on the next plane, train or boat.

Usually the chances of finding the particular bird around when you arrive is slim. The reef heron, I am pleased to report, turned out to be the exception.

Nantucket ornithologist Edith Andrews first spotted the heron roaming a salt marsh April 26, but the sighting did not result in instant consternation. The bird looked a lot like a North American little blue heron, except that it was slightly larger and a darker slate- gray, with a striking white throat and yellow feet. "At first I thought it was just a hybrid," Mrs. Andrews told the local paper. "It never entered my head that it was from another hemisphere."

The bird took up residence in the Quaise marsh, west of the University of Massachusetts field research station. Then, in early June, Robert Cardillo, an ornithological photographer for the Philadelphia Academy of Natural History, on the island for a vacation, took pictures of the "hybrid." Back home, he showed the slides to a specialist associated with the academy who was astonished at the resemblance to a western reef heron.

On July 13, Alec Forbes-Watson and Michel Kleinbaum, two African bird specialists, arrived on Nantucket to verify that this reef heron was the real item. Meanwhile, the possibility that the bird had escaped from some American zoo was ruled out by the Massachusetts Audubon Society and by a check of the International Species Inventory System. The conclusion was inescapable: this bird was an authentic star.

The birding grapevine began to hum. The "Voice of the Naturalist," a telephone service for Washington area bird watchers, notified callers about the bird and called it "that extraordinary exotic visitor from Africa." The Massachusetts Audubon Society established a reef heron hot line and issued a special bulletin with all the pertinent data on the bird: where it is and how to get there.

Fortunately for bird watchers, the heron kept regular hours in front of the research station. Bird watchers could sit in lawn chairs, sip cranapple juice, eat granola bars and observe western reef heron behavior.

Normally a solitary coastal bird, it feeds in shallow surf, sometimes belly-deep in the incoming and receding tides. Fish, crabs and mollusks are its favorite foods. Should a rival bird come too close while it is feeding, it will run toward the invader while emitting a short, throaty squawk.

Soon bird watchers with enough optical equipment to open a store began to appear in flocks. Everyone on Nantucket knew about the bird. My aunt, who has spent 40 summers on the island, visited the marsh for the first time. You could tell an island cab driver, "I want to see the heron," and be whisked off to the precise location without further explanation.

The bird attracted many a lister. (For what it's worth, listers are called "twitchers" in England, and "birdos" in Australia.) According to Paul Dumont of Washington, the reef heron was "the easiest bird in a long time" to add to his North American lifetime list. He flew to Nantucket, spotted the bird and returned to Washington in only 12 hours.

Paul is among the top three North American listers, with 740 bird species out of a possible 840. Normally, he and the 19 other birdwatchers in the elite "over 700 club" have to go to the far reaches of North America to see new birds. Few birds come as easily as the reef heron when you pass 700.

About 645 species are permanent residents or migrants in North America. Another 50 or so are regular or casual migratory species. Those with lists over 700 have seen all but one or two of these birds. The remaining 100 or so birds show up accidentally, as the reef heron did.

Not being in the 700 club myself, I had never had the urge to take off on the spur of the moment and travel to the ends of the earth to see a bird. Never, that is, until the reef heron.

In real life I work for the government. I am the community relations coordinator for the Environmental Protection Agency's Superfund progam. I heard about the reef heron from Joy Chapper, who works on court reform projects for the American Bar Association and is a birding enthusiast like myself. She had seen a newspaper clipping about the heron and called me right away. "Can you make the 10 p.m. plane to Boston?" she asked. Being of sound mind and body, I said no. But a few days later we were in my car on the way to Cape Cod. In tow was my friend Kathy Veit, a program analyst in the Superfund program.

After a trip by ferry to Nantucket, we set out for the marsh on bicycles, equipped with a National Geological Survey map. With only two roads on Nantucket, finding the marsh should have been easy. But we managed to miss the turn and biked 16 miles out of our way.

When we finally arrived at the research station, we quickly scanned the marsh. No heron. A field researcher appeared and reassured us. Five, 10, 15 minutes passed. Still no heron. "What if we've come all this way and don't see it?" Joy asked.

Finally, satisfaction. We heard a squawk and saw the bird of our trip fly over the marsh grasses to its preferred spot. For over an hour we watched the bird preen, feed, and chase other herons and egrets. We broke open the water bottle, which had to substitute for champagne, and passed it around. Chalk up bird number 438, I thought to myself.

Watching the bird, I wondered what would become of it when winter arrived. The heron is a nonmigratory tropical bird. I wondered whether it would go south with other herons, or catch a complimentary flight back to Africa on some helpful airline. And I worried whether it might just freeze to death or be sent to a zoo.

I have asked many people these questions. No one knows. I asked Dick Forster, of the Massachusetts Audubon Society. He said, "the Audubon Society and the field station will cross that hill when they come to it."

Fortunately, the reef heron picked a protected marsh. Other rarities have not chosen so wisely. For example, the Ross' gull, a bird of Siberia and the Arctic Circle, picked an unprotected marsh in Churchill, Manitoba, in which to establish the first known North American breeding colony for its species. Unfortunately for the Ross' gull, an egg or nest collector entered the marsh at night and shoveled up the nest and eggs. The following year the marsh was given protected status.

How the reef heron arrived in Nantucket, thousands of miles from home, remains a mystery. There is speculation that it was caught in a violent storm last spring and was blown far off the coast of West Africa, where it perhaps took refuge on a ship traveling to North America. But the secret of its odyssey is known only to the reef heron.