From 11 to 15 October 2009, we observed Yellow-rumped Warblers (Setophaga coronata coranata) foraging inside an unheated barn on 4 d, and inside a heated modern milking parlor on 2 d at a dairy farm in southeastern Saskatchewan, Canada. Warblers fed on dormant flies that were huddled on the walls inside of the barn and sallied for flies in mid-air and gleaned them from the window screens inside of the milking parlor. These observations were preceded by 2 d of unseasonable cold weather on 9 and 10 October, when maximum temperatures were below 0°C. Yellow-rumped Warblers fed indoors until 15 October after which the days became warmer, and we observed them only outside. Yellow-rumped Warblers most likely entered buildings to feed because unseasonable weather conditions increased their energetic demands and provided incentive for them to exploit shelter and food in novel places.