Warming of the northern hemisphere over the past half-century has spurred research on responses of species to global climate change.  Quantifying the ecological implications of climate change has been severely constrained, however, by a lack of multispecies distributional data by which to compare long-term changes.  The New York State Breeding Bird Atlas, a statewide survey of 5,335 25-km² blocks surveyed in 1980-1985 and 2000-2005, represents one of the few ecological databases in the world with which geographic shifts in breeding ranges of any vertebrate animal can be assessed.  Here we show that, after controlling for range expansion and contraction, the northern margins of southerly species (n = 70) and the southern margins of northerly species (n = 77) have moved northward an average of 11.0 km (P = 0.033) and 8.1 km (P = 0.034), respectively.  All 147 species, showed an average northward range shift of 9.8 km (P = 0.007).  Species did not show a change in elevation.  These patterns corroborate the findings of Thomas and Lennon (1999; Nature 399:213) who observed that range margins of breeding birds in Great Britain indicated a similar northward shift over a twenty-year period.  Although a causal relationship between climate change and species range shift is difficult to establish, this repeated pattern of a northward shift in bird ranges in both North America and Great Britain is compelling.  This study represents one of the first analyses of long-term multispecies distributional changes in North America, and provides further evidence that species ranges are likely moving northward in response to global climate change.