BIRD POPULATIONS - Birdpop.org

DAVID J. ZIOLKOWSKI JR., KEITH L. PARDIECK AND JOHN R. SAUERthe Western, Central, and Eastern BBS regionswith 80%, 90%, and 76% of species increasing,respectively, during 2003-2008 (Fig. 1C). Surveywide,more wetland species demonstratedincrease over the long-term (58%) than not, aresult that appears to be driven by a significantand relatively high proportion of increases in theCentral region (67%). Compared to the longterm,wetland birds apparently fared well during2007-2008, with all regional percentagesexceeding, although not significantly differentfrom, 50%.Scrub/successional species, on the other hand,continued to fare poorly over the long-term anda significantly low proportion of speciesexperienced population growth across all regions(27%, Fig. 1D). The 2003-2008 time periodappeared more favorable for this guild surveywide(49%positive trends), but neither this, norany of the regional values from this period, aredistinguishable from 50%. The 29% of increaseswitnessed in the Eastern region during 2007-2008is the only regional result statisticallydistinguishable from 50%, and it is similar to thelong-term results for this region (24%).During 2003-2008, a significant number ofwoodland birds exhibited increasing trendssurvey-wide (67%), and this was greater than theproportion observed over the long-term (57%;Fig. 1E). This result appears to be driven bysignificant gains made in the Eastern regionduring 2003-2008 (74% increasing trends). The63% of species with increasing long-term trendsfrom the Central region remained nearlyunchanged and significantly high in the 2003-2008 period (64%). In contrast, the proportions ofwoodland birds with increasing trends in allregions during the 2-yr time interval, and alsothose from the Western region during the twolonger intervals, were indistinguishable from50%.Urban bird populations showed a significanttendency for decline in all regions during 1966-2008 (Fig. 1F). During that period, the 42% ofincreasing trends in the Central region balancedout the low 23% seen in the Western region,yielding a survey-wide estimate of just 33% ofurban birds increasing survey-wide. Regionalestimate from the 2003-2008 period are notdistinguishable from 50% but the continent-wideresult of 33% is significant and equivalent to the1966-2008 estimate. Each region exhibited agreater number of declines than increases duringthe 2-yr interval, although only the survey-wideresults (26% increasing trends) and Easternregion results (21% increasing trends) weresignificant.Cavity nesting birds fared relatively well withproportions of increasing species either equal toor significantly greater than 50% in all regionsand time periods (Fig 1G). For instance, 65% ofcavity nesting birds showed positive trendestimates across the entire survey area during2003-2008, including a significantly highproportion of gains in the Eastern region (75%species increasing). During 1966-2008, only theCentral region demonstrated a significantproportion of increasing species (62%).Over the long-term and across the survey,significantly more open-cup nesting speciesexperienced population declines than increases(38%; Fig. 1H). This declining pattern wasevident in Western (34% increasing trends) andEastern (30% increasing trends) BBS regions butnot in the Central region where results wereindistinguishable from 50%. A similar patternwas seen during the 2-yr interval where only25% of Western species and 31% of Easternspecies exhibited increasing trends. In contrast,during 2003-2008, only the Central regiondemonstrated a significant result with 60% ofspecies showing increasing trends.Short-distance migrants did not fare especiallywell over the long-term and only 43% of speciesexhibited positive trends survey-wide (Fig. 1I).This appears to be due in large part to thesignificantly low proportion of populationincreases in the Western and Eastern regions(34% and 30%, respectively), relative to thesignificant number of long-term increases seen inthe Central region (56%). The tendency fordecline in the West and East was similarlyreflected in the 2-yr interval, although theproportions were lower (33% and 26%,respectively), thus dropping the survey-wideestimate to 33% of species increasing during theperiod. Short-distance migrants experiencedtheir strongest increases in the Central regionduring both 1966-2008 (56% increasing trends)and 2003-2008 (63% increasing trends), althoughthe result from the later interval was notstatistically significant.During the long-term and more recent 2-yrperiods, increases in permanent residents did not[96]