When Andy Moore first heard about the herons, he thought the man from the Maryland Wildlife Department was talking about herrings, and he thought it very odd indeed that such creatures had chosen to nest in his birch trees.

"Course it turned out they weren't fish at all, you know," said Andy Moore, the other day, "but great big beautiful birds - most fabulous things you ever saw."

Each spring, for the last 37 years, it turned out, the herons had been coming to Moore's property on Nanjemoy Creek in Charles County to nest, and now Moore has sold the land to the Nature Conservancy to protect what the birds like best - their privacy.

"I've owned that property for 20 years," Moore said in wonder, "and I never knew there were great blue herons on it. Course the herons don't come until the last part of February and they leave in early May, and that's after the hunting season, so it was hard to notice 'em."

Actually, it was a state regional wildlife manager, James L. Weems, who first noticed the rookery, which is the proper name for the high-rise seasonal home of the great blue heron.

Weems said that he first found the rookery about eight years ago while he was flying in a helicopter taking inventory of Charles County beaver dams. Eventually, he was able to locate it from the land as well and took to visiting it two or three times a year to make sure that everything was going well.

And everything did, until Weems made one such pigrimage to the rookery only to hear the sound of falling timber. "It worried me half to death," said Weems, who knew that herons need tall, mature trees in which to conduct the business of raising younger herons.

Weems decided right off that he'd better find the herons' landlord and that's how Andy Moore found out about the herons. "He told me about the lumber contract," Weems said, "and I thought it would help if I took Mr. Moore down to see the birds."

And so, on a cold morning in late winter, Andy Moore and Buddy Weems went to see the rookery. "It was the most amazing thing I'd ever seen," Moore said. "Everywhere you looked there were these little babies stretching their heads out over the top of the nests," and the ground, he said, was purple with the broken, abandoned shells of the heron eggs.

Moore was sold on the herons, but the land itself was up for sale.The idea at the time, in fact, was to sell it to anyone who would buy it fro $1,000 an acre to build second homes on the 150-acre tract.

That was before Moore heard about the highway in Okahoma. "They rerouted it," Moore said. "Four lanes, and they rerouted it, just to save one of these rookeries. It cost several million dollars to do that."

Moore therefore decided to get into the business of preserving rookeries himself, and when it turned out that the state of Maryland could not afford to buy the land, Weems put Moore in touch with the Nature Conservancy.

Moore, who lives in Camp Springs, has sold the land to the Conservancy, a nonprofit conservation group, for half the price he would have received from a commercial developer, he said.

Moore cheerfully admits, "of course," that "we still got a real big profit out of the deal, because we held on to the land for 20 years. When we bought it, it only cost less than $40 an acre."

Altogether, the Conservancy purchased 250 acres, which includes a 100-acre tract adjoining the Moore properly, for a total cost of $133,445. Conservancy officials are currently embarked on a fund-raising drive to raise half the money by Feb. 3, which they must do in order to comply with the terms of the purchase agreement.

Great blue herons have long necks and thin legs and a wanderlust that takes them up and down the East Coast when they are not nesting along Nanjemoy Creek. They fly with their heads tucked back on their shoulders and are fond of insects, mice and frog.