Throughout North America, organized groups of citizens and scientists have collected climate and bird phenology records since the 1880s. Most studies utilizing these data sets have compared mean first arrival dates but have not compared trends between historical and more contemporary data sets. We analyzed spring first arrival dates and fall last departure dates for 39 migrant bird species across three different data sets spanning a historical period when there was little climate change (1888–1939) and a contemporary period during which significant climate warming occurred (1967–2012). During the historical period, there was little change in first arrival dates through time. In contrast during the contemporary period, there was a significant advance in first arrival date from early years to later years. During both the historical and contemporary periods, short-distance migrants reached the breeding grounds earlier than long-distance migrants, and the magnitude of this difference was consistent between periods. During the contemporary period, we found evidence for an increase in breeding season length among 4 of the 39 species studied. Our results suggest that changes in the phenology of migratory bird species in New York are a recent phenomenon associated with a period of climate warming beginning in the mid 1970s and extending through today, but earlier arrival does not appear to be leading to an increase in breeding season length for the majority of species.
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Vol. 129 • No. 2