We documented the effects of hurricane Wilma (2005) on Chimney Swift (Chaetura pelagica) using data from the Québec Chimney Swift Survey Program and observations of swift mortality during migration. Hurricane Wilma developed in the Caribbean and followed the eastern coast of North America, moving over areas used extensively by migrating birds. Thousands of birds and, among them, Chimney Swifts, were caught and carried by the storm as far as Atlantic Canada and western Europe. At least 727 swifts were reported dead. Chimney Swift numbers in the province of Québec, Canada, declined significantly the following year, suggesting adverse consequences of the hurricane on this population over a large area. Roost counts declined by an average of 62%; the total Chimney Swift population decreased by approximately 50%. These results suggest that hurricanes can reduce the breeding population size of some migratory bird species.