It's a crisp October morning in the Annursnac Hill preserve in Concord, Mass., and David Allen Sibley is preparing to summon the creatures he has spent a lifetime observing.

'Last night was the first really cold day of fall, so a lot of birds should be migrating,' says the soft-spoken Sibley. 'I'll see if I can call some in.' Sibley's cheeks work furiously as he begins pishing, 'the making of hissing, shushing, and squeaking noises' to attract birds, according to his third book, Sibley's Birding Basics (Knopf).

Within seconds, two chickadees fly into a nearby apple tree. 'A hermit thrush just flew up in back,' he says, looking through his binoculars and pointing to something in a thicket that is invisible to PW. Soon the air is filled with the chattering of a Carolina wren, the squawks of blue jays and the high-pitched 'seets,' as Sibley describes them, of white-throated sparrows-his kind of conversation.

'Each person develops their own vocabulary for describing bird sounds,' he says. 'It's somewhat personal.'

Sibley, 41, has had plenty of time to develop his. Influenced by his ornithologist father, he has been drawing birds since age seven and first pondered producing his own guide at 12. The Sibley Guide to Birds (Knopf, 2000), the birding Bible that hit the New York Times bestseller list and has 700,000 copies in print, represents 20 years of field study.

'Once in a great while, a natural history book changes the way people look at the world,' the Times wrote of the guide, which covers 810 bird species in North America and includes more than 6,600 watercolor illustrations. It not only established Sibley as the heir to legendary birders John James Audubon and Roger Tory Peterson but also as a preeminent painter of birds. 'The two things have always been complementary,' he says. 'The act of drawing them was the best way to learn about them.'

Since birders tend to own several field guides, competition didn't hamper sales. Despite its three-pound weight (and $35 price tag), the Sibley guide became so indispensable for birders that companies designed packs and clothing specifically to hold it. 'I don't have expectations of doing anything else to equal that,' Sibley admits, sounding both regretful and relieved.

Indeed, demand and publicity for The Sibley Guide to Bird Life & Behavior (Knopf, 2001)-a collaborative effort by 48 birders and biologists that Sibley edited and illustrated-didn't match that of the first book: that work has sold about 160,000 copies. Information on topics such as bird metabolism and breathing may have proved too esoteric for some fledgling birders.

Now, with the slender Birding Basics, which focuses on identifying birds and has a first printing of 175,000 copies, Sibley is hoping to captivate birders across the whole spectrum of experience, much the way his first book did. In fact, the concept grew out of the introduction to that book, which addresses identification but in far less detail.

'I try to explain some of the things that might seem magical-how an experienced birder can look at a distant speck and identify the species,' Sibley says. 'The thought process you go through when you're identifying a bird, the way you can use different field marks and the way the appearance of a bird changes with the weather, the lighting, the time of year. Experienced bird-watchers develop that knowledge through hours in the field, and they do these things without even knowing they're doing them.'

Sibley's first two books were part of a four-book contract his agent, Russell Galen of the Scovil Chichak Galen Literary Agency, negotiated with the book packager Chanticleer in 1994. (Workman publishes a Sibley calendar.) Chanticleer has a long history of collaboration with Knopf, including the National Audubon Society Field Guide series. But Knopf brought out Birding Basics alone because production was a much simpler matter. Sibley's editor, Susan Ralston, made the book's tone more informal and reader-friendly, a change Sibley applauds.

Sibley is in the midst of a 20-city book tour, giving him the chance to lead bird walks all over the country. Typically, with his packed work schedule, he gets out in the field only a couple of hours a week. And birding is more complicated for him these days because people recognize him. 'I'll meet people, and they'll want to have books signed,' he says. Recently, he overhead a birder say, 'Hand me the Sibley!'

An ornithology student, Sibley left Cornell in his freshman year and spent the next 12 years, from 1980 to 1992, crisscrossing the country in a van, studying and painting birds. 'Birds are so exciting, so visible, so varied and so mobile,' he explains. 'Seeing rare birds, of course, is the most exciting part of birding.' During that period, he took only bird-related jobs to support himself. While banding songbirds at the Manomet Bird Observatory in Plymouth, Mass., he met his future wife, the ornithologist Joan Walsh. They have two sons, Evan, eight, and Joel, five.

Since 1999, the Sibleys have lived in Thoreau country, just two miles from Walden Pond. At the Concord Bookshop in town, a Sibley display takes up one window. The store had already sold 104 copies of Birding Basics just five days after its release.

Next year, there will be more books for the window. Sibley is working on field guides to eastern and western North America, both due out in April 2003. He also has been collecting corrections and fine-tuning illustrations for a second edition of the first guide, though no date has been set. And he's under contract for two more books from Knopf.

Like his others, these books will focus on North America, which he says holds enough interest to occupy him for a lifetime: 'I'm just getting to the really interesting questions now.' And some of those, he hints, may even explore aspects of the natural world beyond birds.