More important, a pair of innovative and beautiful bird books has recently been published by two of the country's best known birders, David Allen Sibley and Kenn Kaufman.

At more than 2 1/2 pounds, "The Sibley Guide to Birds" (Knopf, $35) is the larger and more heavily praised of the duo. In ornithological circles it's been called "a quantum leap," "the high water mark for bird guides," and "a natural history book that changes the way people look at the world."

Kaufman's "Birds of North America" (Houghton Mifflin, $20) is no less unique. It incorporates an entirely new method of organization enhanced by the first-ever field guide use of digitally altered photographs.

These books come at a time when birding is the fastest-growing recreational activity in the country. Locally, the Seattle Audubon Society sells a ton of bird seed a week from its retail store in Seattle's Wedgwood neighborhood, and fills more than 150 field trips per year. "I know that I see a lot more kids birding in Seattle now than when I was a kid in Tennessee in the 1970s," says Helen Ross, the society's local conservation coordinator. "I have also noticed that birding is starting to cross ethnic and age boundaries."

Like Ross, Sibley and Kaufman started birding as youngsters. Like many kids, Kaufman was interested in the exotic aspects of nature such as tigers and volcanoes, but quickly realized he wouldn't find them in Indiana. "I started looking at birds because they were all around and I quickly discovered that they were fascinating creatures," he said in a recent interview.

Sibley was born into a bird-oriented family. He learned to bird from his father, ornithologist Fred Sibley, who directed the Point Reyes Bird Observatory and later curated vertebrates at the Peabody Museum of Natural History at Yale. "I started birding when I was 6 and tracing bird pictures from Arthur Singer's `Birds of the World' at 7," Sibley said prior to a recent speech in Seattle.

He started sketching birds in the field, and by age 12 knew he wanted to do a field guide. "I pictured a book that was more complete and filled with more details and more illustrations than any other," he said.

He has done so. The Sibley guide contains more than 6,600 gouache paintings of 810 species and 350 regional populations. Instead of one or two drawings of each bird, he includes an array of plumage patterns from drab juveniles to colorful breeding adults, as well as birds in flight. For example, dark-eyed juncos are represented in 29 different drawings.

Good layout was also a concern. "Turn to any page, and all the birds have the same plumage across the page, so you can easily compare one species to the other," Sibley said. "All the birds face the same way and all are drawn at the same scale."

Sibley used a method pioneered by Roger Tory Peterson in his field guide - details that aid in identification are placed next to each bird, generally with a line pointing to a specific feature. However, Sibley uses up to 15 additional identification pointers per bird.

Kaufman also had aspirations from a young age. "I have fantasized putting together a guide since I was 11," he says. "The idea for this one, though, came about from a conversation with Roger Tory Peterson," the godfather of all bird artists and bird-guide authors.

Peterson had just released his Western States guide. "Roger said he had included too much detail. Most guide books, his included, he said, were written with the assumption that the user would know what he was looking for before he had even opened the book. After this conversation, I decided I wanted to put together a book for someone who had never birded before."

Like Sibley, Kaufman has departed from the normal bird guide. Instead of organizing birds taxonomically, which puts loons first and finches last, he has placed birds into distinct groups such as "Ducks, Geese, and Swans" or "Chicken-like Birds." These are further subdivided into categories, with all birds within a group sharing a similarly tabbed color code.

"To emphasize the more common birds," Kaufman says, "I put them at the top of the page. I wanted to make it easy to find the birds that a beginner would notice."

Kaufman's other innovation is his use of technology. Kaufman scanned more than 2,000 photographs and invested more than 3,000 hours in digitally altering them for consistent size, color, and lighting to make them easier for beginners to identify.

Both authors have carried their childhood passion into adulthood. "I have continued to bird because it is so unpredictable," says Sibley. "You know that birds are always around you, but you never know which exact birds you are going to see. An additional part of the excitement of birding for me is the intellectual challenge of identification. It's a reasoning puzzle. You look for a clues to deduce a name and from there you put the bird into a larger picture."

Kaufman supplemented this aspect of naming by noting its importance to conservation. "Learning names helps you create a three-dimensional picture of the bird's environment," he says. "You know where it came from and where it's going. A name is an initial step in developing appreciation for nature, which in turn leads toward a better chance for protection."

In a society that places so much importance on speed and quickly turning out products, it is a pleasure to see the results from two people who have devoted their lives to quiet, careful and detailed study.