ENHANCING THE SCIENTIFIC VALUE OF THE CHRISTMAS BIRD COUNT

THE CHRISTMAS BIRD COUNT (CBC), conducted by the National Audubon Society (NAS) since 1900, constitutes the longest-running and geographically most widespread survey of bird life in the Western Hemisphere. Starting with 25 count locations in its first year, the program has grown continuously ever

since, with 20-30 locations currently being added annually. Each CBC consists of a tally of all birds detected within a circle 24.1 km (15 miles) in diameter, on a single day within a few weeks around Christmas (current allowable dates are 14 December through 5 January). More than 50,000 observers now take part each year, in close to 2,000 count circles spread across the U.S. and its territories, southern Canada, and, increasingly, Latin America.

Christmas Bird Count data have been used in hundreds of publications on a wide range of topics. Many papers describe general biogeographic patterns of bird distribution and abundance in winter (Bock et al. 1978, Bock and Ricklefs 1983, Bock 1984, Root 1988a). Others focus on changes in bird life over time, including changes in distribution (Bock and Lepthien 1976a, Root and Weckstein 1994, Duncan 1996, Pranty 2002) and abundance (Graber and Golden 1960, Bock and Lepthien 1976b, Lepthien and Bock 1976, Yunick 1988, Brennan and Morrison 1991, Sauer et al. 1996). Studies of broad-scale population irruptions are often based on CBC data (Bock and Lepthien 1976c, Bock 1982, Yunick 1984, Davis and Morrison 1987, Smith and Scarlett 1987). Increasingly, CBC data are used to test specific hypotheses about causes and patterns of population change (Dunning and Brown 1982, Hagan 1993, Alien et al. 1995, Viverette et al. 1996, Hochachka and Dhondt 2000, Bonter and Hochachka 2003, Caffrey and Peterson 2003).