As a volunteer in the National Audubon Society's annual Christmas Bird Count, Jennifer Supplee has braved freezing cold and snowstorms, and even donned hip waders to deal with torrential rains.

This morning, the Downingtown woman was planning to be up by 2:30, hoping to hear great horned and eastern screech owls in Valley Forge Park with other bird counters from the John James Audubon Center at Mill Grove.

"You really don't see them unless you are really lucky," said Supplee, who did manage to catch a glimpse of an great horned owl last year during a spring count.

Supplee is one of almost 60,000 field and feeder watchers who participate in the annual bird census, held over three weeks starting Dec. 14 throughout North and South America, the Caribbean and the Pacific.

"So many people are not aware of the treasures lying up in the trees," said Supplee, who has been involved in the count since 1998 and birding since her childhood.

The 108-year-old event, the world's oldest wildlife census, began as an alternative to a Christmas shoot. Back in 1900, the first 27 participants staked out 25 locations and began counting instead of killing birds.

The counts occur in 15-mile circles that are further divided into sections. Every bird that is heard or seen makes the list.

About a dozen Christmas Bird Counts happen every year in the Philadelphia region, according to Vincent Smith, president of the Valley Forge Audubon Society and a Christmas Bird Count volunteer.

The count gives scientists "a feel for the status of birds in general," Smith said. He added that data had been used to track the decline of certain species, such as the rusty blackbird, whose numbers have been dropping since the 1960s.

"Even in the 10 years I have been doing the count, I have noticed a decline in the amount of warblers coming into our areas," Supplee said.

Edie Parnum, 70, of Wayne, who compiles the data for the Mill Grove group, has been a birder for about 25 years. Over 24 hours, Parnum says, about 60 local volunteers will count 23,370 birds from about 75 species.

Sparrows, robins, house finches, tufted titmice, Carolina chickadees, crows, blue jays and Canada geese are some of the more common species found in their count area, which includes Valley Forge Park, Pickering Creek, and Norristown Farm Park.

"It is especially fun to find a bird that is a little less common," Parnum said.

She was hoping that the Baltimore oriole, which made a Christmas Day appearance at her birdbath last year, will make a return visit today in time for the count. "I would like to see that again," she said.

Contact staff writer Mari A. Schaefer at 610-892-9149 or mschaefer@phillynews.com.