The brown thrasher is a strong, but partial migrant, as the bird is a year-round resident in the southern portion of its range. The breeding range includes the United States and Canada east of the Rocky Mountains, but has been occasionally spotted West of the Rockies. The increase in trees throughout the Great Plains during the past century due to fire suppression and tree planting facilitated a westward range expansion of the brown thrasher as well as range expansions of many other species of birds. Studies indicate that thrashers that reside in the New England region of the United States during the breeding season fly toward the Carolinas and Georgia, birds located in the east of the Mississippi winter from Arkansas to Georgia, and birds located in the Dakotas and the central Canadian provinces head towards eastern Texas and Louisiana. When the species does migrate, it is typically for short distances and during the night. There are also records of the bird wintering in Mexico, as well as a British record of a transatlantic vagrant.