Using Christmas Bird Count data to assess population dynamics and trends of waterbirds

AMERICAN BIRDS 23 We are especially interested in CBCs done since 1965–66 for two major reasons. First, the U.S. Geological Survey’s Breeding Bird Survey (BBS) started in 1965, and we are interested in comparing population trends and annual indices derived from CBC and BBS, especially for permanent resident species with a large portion of their range in the 48 contiguous United States and southern Canada, the areas that are best surveyed by both the BBS and CBC. Second, CBC methodology has been relatively stable since 1965–66, increasing the odds that population changes indicated by CBC data over the past 40 years would be due to actual population changes rather than changes in counting methods. Our goal is to complete the analysis of population dynamics and trends for all species that have been encountered on 40 or more CBC circles in the past 40 years (and for even rarer species if the statistics suggest the analyses are valid). We want to compare BBS and CBC trends for all species encountered by both surveys for several reasons: 1) to be sure that the surveys are providing similar results when similar results should be expected (especially for resident species with most of their ranges in the contiguous states and southern Canada), 2) to determine which survey is most likely to provide the most useful data on population trends and dynamics, based primarily on percentage of the range and percentage Using Christmas Bird Count Data to Assess Population Dynamics and Trends of Waterbirds On the decline: Analyses of both the Christmas Bird Count and Breeding Bird Survey show that the American Bittern (Botaurus lentiginosus) is significantly in decline. Illustration/John James Audubon