Working in his store in Layton, waiting on the customers who come in to buy birdseed, Bill Fenimore made a discovery. He discovered that most bird books are too big and too complicated for the casual bird-watcher.

The casual bird-watcher is the kind of person who looks out the kitchen window and wonders, "What is that orangey-red fellow?"

A casual bird-watcher does not need a bird book as thick as a phone directory. She does not have the patience to read about every bird in North America. He gets confused trying to compare the size of the bird in his back yard to the size of the bird on the page.

A couple of years ago, Fenimore started dreaming of the kind of guide he'd like to sell in his store. He thought it should feature only the 25 most common birds in any given state. He thought he'd arrange his data according to the size of the bird. That way, if you saw a large bird, you could just flip to the back of the book and start looking at photos of hawks.

In early April, the first five books in Fenimore's "Backyard Birds" series were published — "Backyard Birds of Utah" plus books for California, Pennsylvania, New York and Maryland.

In late April, on a windy Saturday morning, Fenimore led a troupe of bird-watchers on a stroll through the Ogden Nature Center. Five-year-old Tyman Felix kept close to Fenimore as they walked. Each time Fenimore pointed to a tree, the little boy would raise his bright yellow binoculars.

After they spotted a chickadee, Fenimore asked the group to practice its call. "Chick-a-dee, chick-a-dee." Fenimore explained how these birds warn each other of danger by adding to the number of "dees" at the end of the call.

Cornell scientists are the ones who discovered that "Chick-a-dee," means "Bill's headed for his backyard feeder," Fenimore said. But "chick-a-dee-dee-dee-dee-dee-dee" means "Here comes a hawk!"

After they'd walked together for a half-hour or so, Tyman confided in Fenimore, "I've got one of your books in my backpack." Fenimore grinned.

He knelt by the boy and helped him dig out "Backyard Birds of Utah," and they looked at it together. They looked at the photo of the black-capped chickadee and decided, sure enough, it was the one they'd just seen.

Tyman did not appear to be able to read. But he seemed able to understand the size scale at the bottom of the page.

The scale shows seven pale silhouettes, ranging in size from hummingbird to crow. On the chickadee's page, the second largest silhouette was highlighted in red, offering a visual clue that the chickadee is a bit larger than a hummingbird, about the size of a wren.