Thousands of birdwatchers in the United States, Canada and Latin America were out in force from mid-December to the beginning of January taking part in the 112th Christmas Bird Count, sponsored by the National Audubon Society, a U.S. bird conservation organization.

Data collected from the annual exercise helps scientists understand how environmental changes affect birds.  

Huntley Meadows Park in Fairfax County, Virginia, is home to a wide variety of birds. That's where Ana Arguelles and her husband, Jeff Wneck, who live next to the 588-hectare wetlands, take part in the annual count.

?I want to keep seeing birds in the future, and this is the way I feel I can help,? says Arguelles.   

They are joined by other volunteers, carrying binoculars and bird books. Birding is the second most popular hobby in the United States.

?They?re pretty. They?re fun to watch," says Ray Smith, who has traveled around the world on birdwatching expeditions. "They?re interesting to know about. ?

He uses a telescope and binoculars to get close-up views. Arguelles tallies the number of species the group has identified.

Ruth Goetz spots an egret, which is not usually seen in the park during winter. "It?s just amazing the variety of birds you find here.?

Goetz and her son, Joel, 12, are attending their first Christmas bird count.

?I think that it?s an important part of researching birds and finding out how the bird populations are doing," Joel says, "and I think it?s also fun. ?

The day gets even more exciting when a rarely-seen merlin and another bird chase each other. Smith takes a photo of the small falcon using his telescope and a camera phone. The merlin, one of the world?s fastest birds, is a rare sight at Huntley Meadows.

"It?s powerful," says Arguelles. "You know, the bird has character. It really gets you going.?

Bird count data show the population of merlins and other birds is decreasing.  

Audubon Chief Scientist Gary Langham says that's primarily because of habitat destruction. "Just in the last 40 years, almost all species of birds? populations have decreased between 40 and 80 percent.?

The data also show North American birds are shifting their winter ranges farther north.  Langham believes that?s because of rising temperatures due to climate change.

?There?s going to be significant range shifts over the coming years in response to a warming planet,? he says.

The information collected over more than a century of counts helps scientists identify bird species at risk and suggests ways to protect their habitats and breeding grounds.

Arguelles says that's important because people and wildlife rely on the same ecosystems. ?If we protect the wildlife in natural environments, we are protecting ourselves.?

She appreciates that Huntley Meadows Park is a refuge for birds, and for people who want to enjoy their beauty.