Tropical cyclone activity predicts autumn vagrancy of Nearctic birds on a remote North Atlantic island.

Wind drift has long been invoked as a primary driver of the seasonal appearance in Europe of long-distance migrants from North America (‘Nearctic vagrants’), presumed to be displaced beyond their normal range by westerly crosswinds and tropical storms encountered during migration. Yet few studies have tested how tropical cyclone (TC) activity shapes long-term patterns in offshore vagrancy. I assembled a 20-year autumn time series (2005–2024) from the small oceanic island of Corvo (Azores, Portugal) and used generalized linear models (GLMs) to relate fluctuations in Nearctic vagrancy to meteorological indices of TC activity. Across ~900 days of sampling, 126 TC events coincided with field effort, during which 1,660 individuals representing 111 Nearctic taxa were recorded. Both TC frequency and vagrant counts increased over the study period, and autumns with more sustained, basin-wide North Atlantic cyclonic activity tended to yield more species and individuals on Corvo. To assess short-term timing, I fitted GLMs to a focused subset of October landbirds from 2017 onward (8 years), comparing candidate temporal lags; the best-supported model incorporated a 5-day lagged response to TC activity. Overall, these results indicate that vagrancy on this remote island is, at least in part, cyclone-driven. Given projections of greater variability and more active TC seasons under climate change, Nearctic vagrancy in the North Atlantic may correspondingly increase in the years ahead.