CITIZEN SCIENCE AND BIRD–DISTRIBUTION DATA: AN OPPORTUNITY FOR GEOGRAPHICAL RESEARCH*

Biogeographers are often interested in processes and patterns that occur at large spatial scales, but the logistical difficulty of sampling at such scales limits their work. Although satellite imagery is useful for measuring plant communities at large scales, it can generally only provide zoogeographers with habitat measurements and not observations of animals themselves. An alternative strategy for obtaining animal data over large geographical areas is to enlist the help of amateur naturalists to collect data on a large scale, an approach that has been most effective for birds. Since the coming of age of bird-watching as a sport and hobby in North America in the mid-1970s, a community of thousands of skilled amateur ornithologists has emerged. These volunteers regularly search out birds over most of the contiguous United States and southern Canada and have become efficient at reporting their observations to a variety of central data clearinghouses. The enlistment of amateur naturalists to collect ecological information has come to be known as "citizen science." In this essay I discuss the most useful publicly available avian databases and the advantages and limitations of each. THE AUDUBON CHRISTMAS BIRD COUNT The venerable Audubon Christmas Bird Count (CBC) is a tradition that stretches back over a century. The CBC is by far the largest bird-counting effort on the globe. In the winter of 2008/2009 it comprised 2,124 counts, of which 1,673 were in the United States, 361 in Canada, and 90 elsewhere (LeBaron 2009, 2). The CBC is conducted in a period of two to three weeks from mid-December to early January. Each CBC covers a circle 15 miles in diameter. Usually a volunteer count compiler carves the circle into territories and assigns each territory to a "party" of birders who travel together. The same group of bird-watchers often covers the same territory for years in succession. On count day, birding parties search for birds while keeping track of their total hours in the field birding by foot and by automobile. Bird researchers typically divide the resulting bird counts for individual species by the "total party hours" amassed on a CBC, if they wish to compare bird counts among years or different locations. For species whose habits make them unlikely to be detected from inside a vehicle, dividing counts by "party hours on foot" may be preferable. Miles by automobile and on foot are also reported, and they may be the appropriate adjustment factors for some species. Although the great strength of the CBC is its impressive scale, its weakness is its recreational flavor. Birders often focus on amassing a large species list or finding rarities and may bias their efforts toward the habitats most productive for such activities. Their attempts to find and accurately count commonplace species may be less fastidious. No standardization or documentation of the proportion of time spent in particular habitats exists, nor does the use of specialized counting procedures--using audiotapes of owls to attract mobbing songbirds, for example--which can vary among birding parties. For species that use specialized habitats or that are usually detected under a narrow set of circumstances, interpretations must keep these factors in mind. For instance, almost all reports of hummingbirds in their Louisiana-Mississippi winter stronghold come from residential yards specially planted for them, making their counts dependent on the degree to which the CBC compiler has solicited coverage from stay-at-home feeder watchers. Despite these caveats, many researchers assume that intercount differences cancel out sufficiently over the large number of counts and observers to make CBC data useful, and the sheer scope of the CBC makes it appealing for research. Weather variations may have serious consequences on birder behavior and bird detection, but they can be dealt with by eliminating years with high winds or intense precipitation. …