BIRD POPULATIONS - Birdpop.org

NORTH AMERICAN BREEDING BIRD SURVEY 2003-2008INTRODUCTIONInitiated in 1966, the North American BreedingBird Survey (BBS) is the primary source ofstandardized population data for breeding birdsin the U.S. and Canada. For most avian breedingspecies in North America, it is the only availablesource for long-term population trend estimatesand relative abundance measures at largegeographic scales. The BBS was initiated by theU.S. Fish and Wildlife Service and CanadianWildlife Service and is currently administered bythe U.S. Geological Survey (USGS) and CanadianWildlife Service (CWS). In 2007, Mexico’sNational Commission for the Knowledge andUse of Biodiversity (CONABIO) partnered withthe USGS and CWS to expand the BBS intoMexico. A sampling framework, includinghundreds of new routes, is currently indevelopment across the northern tier of Mexicanstates, putting the survey closer to its goal ofmaking the BBS a fully North Americanprogram.This summary presents continent-wideestimates of population trends for 422 birdspecies and four species groups [Western/Clark’s Grebe (Aechmophorus clarkii/A.occidentalis), Willow/Alder Flycatcher(Empidonax traillii/E. alnorum), Pacific-slope/Cordilleran Flycatcher (Empidonax difficilis/E.occidentalis), and Yellow-bellied/Red-naped/Red-breasted Sapsucker (Sphyrapicus varius/S.nuchalis/S. ruber)] for the period 1966-2008.Although these four groupings currently consistof taxonomically distinct species (AOU 1998),each was viewed as a single taxon when the BBSwas initiated and early data collected from areasof sympatry cannot be discriminated adequatelyto permit contemporary range-wide species-levelanalyses. In this report we discuss the 6-yrtrends, 2003-2008, and 2-yr trends, 2007-2008,within the context of long-term changesestimated over the 1966-2008 interval. Detailedanalyses and discussion of population changesfor individual species within specific regions,states, provinces, territories, and physiographicstrata are beyond the scope of this summary.Also included in this summary are thecontinental and regional trends for 12 groups ofbirds sharing similar life-history traits. Analysesof group trends can provide insight into thebroad temporal and geographic patterns ofpopulation trends, especially when viewed in thecontext of previous BBS summaries (Pardieckand Sauer 2007, 2000; Peterjohn and Sauer 1993;Peterjohn et al. 1994, 1996).METHODSThe BBS consists of over 4600 active surveyroutes randomly located across the continentalUnited States, Canada, and northern Mexico [Seethe North American Breeding Bird Survey website (www.pwrc.usgs.gov/bbs/) for mapsdepicting the approximate locations of theseroutes]. Since 1994, the number of routessurveyed in the United States and Canada hasremained relatively constant at about 3000 routes.A total of 2980 routes were sampled in 2003, 2995in 2004, 3059 in 2005, 3058 in 2006, 3111 in 2007,and 3022 in 2008.The BBS methodology is described brieflyhere; see Robbins et al. (1986) for a detaileddescription. The BBS is a roadside surveyprogram consisting of 39.4-km (24.5-mi) routes,with stops placed at 0.8-km (0.5-mi) intervals fora total of 50 stops. Routes are randomlyestablished on suitable roads and surveyed onceper year during the height of the breeding season(June for most of the U.S. and Canada). At eachstop, a skilled amateur or professionalornithologist records all birds seen within a 0.4-km (0.25-mi) radius and every bird heard, duringa 3-min point count. For each species, the sum ofthe counts from the 50 points is used as an indexto abundance along the route for that year.ESTIMATION OF POPULATION TRENDPopulation change was estimated using ahierarchical log-linear model fit to BBS data withMarkov chain Monte Carlo (MCMC) methods.Hierarchical models provide a natural frameworkfor accommodating differences in qualityof information among regions and the MCMCprocedure provides a convenient tool forestimating composite results. The hierarchicalmodel analysis was first described by Link andSauer (2002) and we note that this report is theinaugural summary report using this analysis.Sauer and Link (2010) conducted a comprehensivecomparative analysis of BBS data usinghierarchical model and route regression results,and we refer readers to that evaluation for detailsof both the analytical method, its implementationfor BBS data, and the similarity of results[91]