Ruby-throated hummingbirds sense when days become shorter and use the information to determine when to migrate, according to Penn State University. They fly about 600 miles across the Gulf of Mexico in the fall to reach Mexico and Central America.
According to Penn State University, ruby-throated hummingbirds leave Pennsylvania in September. They return in mid-April to early May.
Penn State University recommends taking down hummingbird feeders in September. Keep an eye on the feeders, and take them down when you don't see any hummingbirds for a period of 1 week or longer.