Justin Schwemmer, 10, remembers finding the impression of an owl's wings in the snow, and the tiny footprints of a mouse nearby.
"The trail of the mouse ended right where the wing prints were," says his mother, Sharon, an avid bird-watcher.
Danny Schwemmer, 7, enjoys identifying the birds that visit his family's many feeders -- it's like piecing together a puzzle.
And the youngest Schwemmer, 2 1/2 -year-old Marshall, plays peek-a-boo with the woodpeckers that feed in his backyard on a homemade mixture of peanut butter, corn meal, flour and shortening. He points to the "tee," or tree, where his avian playmates come to feed.
The Schwemmer home, on 2 wooded acres west of Hampstead, is a stage for many of nature's vignettes. The backyard adventures with birds and other creatures are second nature for the boys, like digging in a sandbox or diving into a pile of fallen leaves.
For the Schwemmers, some experiences are more than fleeting. For weeks last year, the family watched a pair of great-horned owls -- powerful, nocturnal predators -- raise young in a nest just 100 feet from the house.
The family's practice of feeding birds, putting up nest boxes and keeping track of migratory visitors is a window on a world of endless discoveries.
And their hobby is one shared in varying degrees by thousands young and old. The cost can be minimal and the rewards priceless.
You can get started as a backyard bird watcher for less than $10, with a board tacked to a window sill to serve as a feeder and a bag of mixed seed from the grocery store. Binoculars, if necessary, can cost as little as $25 at discount stores.
If you don't want to bother with making your own platform, try buying a small, inexpensive feeder that can be stuck to a window with suction cups. Or simply spread seed on a tree stump and the ground.
The birds don't care whether your feeder is an Escort or a Cadillac, as long as there is food. All the better if you have a hanging feeder or one fixed to a window, and seed spread on or near the ground. Goldfinches, Carolina chickadees, woodpeckers and other species prefer the former. White-throated sparrows, cardinals, mourning doves and other species prefer the latter.
Mrs. Schwemmer, 35, was first bitten by the bird-watching bug when she was in elementary school. She has a vivid memory of her sense of accomplishment when she was first able to use a small pocket field guide to identify a bird on a feeder at her grandparents' summer home. "I ran to my mother and said the whole name: 'rufous-sided towhee.' "
She became more serious when she and her husband, Geary, a scientist at NASA's Goddard Space Flight Center in Greenbelt, took a field guide to birds while on a trip out West in 1977.
For some people, backyard discoveries lead to questions -- and an understanding of how people influence the well-being of birds and other critters, and vice-versa.
How has backyard feeding expanded the range of cardinals and other birds? What role do birds play in keeping insects in check or spreading seeds of many native plants? How has the importation of starlings and house sparrows from Europe affected populations of native birds of suburbia?
"I like to study animals that are getting extinct, especially birds," says Justin.
And the discoveries can be just as thrilling if you live in the Carroll County countryside or in downtown Baltimore, like 74-year-old Peggy Bohanan.
"Anything can show up in the city," says Mrs. Bohanan, who has been bird-watching for about 30 years. She has compiled a "yard list" of 118 bird species that have come to feed during the winter, rest during migration or are seen flying overhead.
Her 15-by-30-foot yard, as well as several other small yards behind neighboring row houses, provide an island of maples, hollies, dogwoods and other plant species in a sea of concrete.
For some, an awareness of birds in their backyards leads to spring walks with more experienced members of the Maryland Ornithological Society along the shores of Lake Roland just north of the city, or elsewhere. It also may lead to participation in annual counts of birds in winter or spring.
If the birding obsession takes hold, it can take you to strange places in search of rarities, as it did the hundreds of people who flocked to Back River Waste Water Treatment plant near Essex in March 1990 for a once-in-a-lifetime look at a Ross' gull, a bird never before seen in Maryland. The closest nesting spot for the species is Churchill, Manitoba, along Canada's Hudson Bay. It breeds more commonly in Siberia.
Bird study, either through a kitchen window or in the wind-swept marshes of Chesapeake Bay, feeds a $1 billion industry of selling field guides, binoculars, seed and other paraphernalia. The U.S. Fish and Wildlife Service estimates that more than 82 million Americans feed wild birds.
Some people combine bird study and gardening, by cultivating berry-producing species, flowering plants and cover to attract birds.