From declines to recovery: 52 years of changes in autumn migratory songbird abundance at an island stopover site in southern New England

ABSTRACT Migratory birds are declining across North America, and many studies have used long-term datasets to estimate trends in abundance for migratory birds. To prioritize at-risk populations most efficiently, it is critical to know the current trend status of migratory species, which involves accurately assessing the most appropriate timescale for monitoring changes in populations. In this study, we analyzed autumn bird banding data from the Block Island Banding Station on Block Island, Rhode Island, USA, over a 52-year period (1970–2021), focused exclusively on hatch-year birds, to examine long-term abundance trends for 22 species of migratory songbirds and compared our results to trends from Manomet Conservation Sciences and the USGS Breeding Bird Survey. We ran 4 models (no change, linear, quadratic, and breakpoint) for each species and used model selection with AICc to determine the best model. Eighteen of the 22 species were best represented by breakpoint models, indicating that they experienced a sudden change in slope during the study period. All 18 breakpoint species experienced the largest decline in the first 2 decades of the study (between 1976 and 1986), and 17 of 18 species were stable or recovering after the breakpoint. Of the 4 species without a significant breakpoint, 1 had no change over the study period, 2 were best represented by linear models, and 1 was best represented by a quadratic model. Trend classifications varied across time, methods, and the geographic regions of the subpopulations sampled. These results present evidence that despite initial declines, many species are currently stable or in recovery. We also highlight that modern conservation efforts need to account for abrupt changes in trend direction within long-term time series analyses to most accurately assess current abundance trends for the conservation of vulnerable species.