32 YEARS OF CHANGES IN PASSERINE NUMBERS DURING SPRING AND FALL MIGRATIONS IN COASTAL MASSACHUSETTS

Abstract

Using standardized mist-net captures collected over a 32-year period (1970–2001), we examined changes in the capture rates of passerines recorded in coastal Massachusetts during fall (78 species) and spring (72 species) migration. Capture rates of 45 species of fall migrants (58%) declined significantly between early (1970–1985) and late (1986–2001) years of the study; 36 species of spring migrants (50%) showed significant declines. Only Carolina Wren (Thryothorus ludovicianus), Tufted Titmouse (Baeolophus bicolor), Northern Cardinal (Cardinalis cardinalis), and Orchard Oriole (Icterus spurius) showed significant increases during spring migration; fall sampling indicated that Carolina Wren, Tufted Titmouse, Black-throated Blue Warbler (Dendroica caerulescens), and Northern Cardinal had significantly higher capture rates. Of 37 species included in the migration monitoring data but not reliably represented by Breeding Bird Survey (BBS) data in any of the northeastern physiographic strata, 23 (62%) showed significant declines at Manomet during at least one of the two migration periods. There were significant correlations in percent changes in migrant capture rates between fall and spring. BBS trends reported from the southern New England and northern New England physiographic strata were correlated with changes in migrant capture rates. However, there were also inconsistencies between results obtained by the two monitoring approaches, suggesting that factors in addition to actual changes in breeding populations may be reflected in the migration capture data.