"It has become a popular event for regional birders who are assigned specific miles to cover," Ryan said.
Ward and Miskovsky were covering four miles, heading upriver from Cushwa Basin. As members of the D.C. chapter of the Audubon Society, the couple said they have been volunteering for the survey for the past several years.
"It's a fairly methodical process," Miskovsky said. "We have a data sheet where we record any species we see, plus time and weather. In addition to birds seen along the towpath, we also include species found on the Potomac River."
Ward said she has been an avid bird-watcher for the past 15 years, but had been hesitant to participate in the survey until she was given some encouragement about four years ago.
"I was surprised to find it wasn't as difficult as I thought it would be," Ward said. "Plus, you have a chance to explore some very lovely areas along the canal."
Two important pieces of equipment were needed for the survey, Miskovsky said: "Our ears and our eyes, supplemented by binoculars."
The couple had just started out on their journey when they spotted a Carolina wren.
Other birds common to that section of the canal include cardinals, mockingbirds and juncos, they said.
With this year marking the culmination of the survey, Miskovsky said he's interested in seeing the trends over the past 10 years.
Data also could reveal the effects of global warming, Miskovsky said.
"Population trends could tell us if more Southern species are being found farther north in winter than usual - the result of warmer winters," he said.
Miskovsky said he always has been interested in nature and ecology, but became an avid bird-watcher some years ago after visiting Central America.
"You can't not become a birdwatcher after a trip like that, where the bird population is incredible," he said.
David Smith of the Audubon Society's Central Maryland chapter was walking a five-mile stretch upriver from Cedar Grove.
"This has been a good day," he said. "I saw a lot more waterfowl than usual, and also spotted a bald eagle."
Over the last nine years, volunteers have recorded 113 different species of birds during the count, Smith said.
"I'm not sure, but I might have added a new one this year," he said. "I spotted a snow goose and that's not on the current list."
Ryan said Saturday's tallies of species and numbers will be recorded into a database indexed by towpath mile. The data will be posted on the D.C. Audubon Society's Web site at www.dcaudubon.org/canal.