In an annual holiday tradition, tens of thousands of volunteers from Alaska to Antarctica look and listen for birds to count populations for researchers. The National Audubon Society organizes the Christmas Bird Count (CBC) to track species from mid-December to January 5.
Participants throughout the US, Canada and 19 other countries in the Western Hemisphere count birds over a defined period along a specified route in a 15-mile (24-km) circle. Armed with binoculars, guides and checklists, the volunteers join scientists in the conservation project, identifying and recording different species.
Some watch home feeders in designated areas while the majority observe in the field to compile data on thousands of birds from the Northern Shrike to Cackling Goose.
Since Christmas Day in 1900, the annual Bird Count began as an alternative to bird hunting and a solution to declining bird populations. Organized by an ornithologist at the American Museum of Natural History, Frank Chapman, the inaugural event happened in New York City's Central Park, which the Audubon Society continued when it formed in 1905.
The data collected by the CBC observers over the past century has allowed researchers and conservation biologists to study the health of bird populations, such as the decline population of American Black Ducks in the 1980s, which resulted in reduced hunting of the species.
Research has also contributed to the first US State of Birds Report in 2009 from the US Department of the Interior. The CBC analysis revealed the dramatic impact of climate change on bird populations. With habitat destruction and warming temperatures, birds are shifting their winter ranges northward and inland.