The phrase "fall migration" refers to the movement of animals, such as birds, from one place to another during the autumn season. They travel to find better climate conditions, food, or breeding grounds.
The centerpiece was inspired by the annual fall migration of several birds and butterflies that pass through Texas on their way to Mexico. (decortoadore.net)
Each February, the Golden Gate Raptor Obesrvatory (GGRO) recruits field and outreach interns for the following fall migration season. (parksconservancy.org)