Snowy owls periodically irrupt southward in large numbers during years of lemming population crashes on the Arctic tundra. Southern irruptions expose naive young owls to vehicle strikes, power line collisions, and starvation in unfamiliar habitats.
Snowy owls in unfamiliar urban and suburban environments during irruptions encounter threats they have no evolutionary experience with. Vehicle strikes cause traumatic injuries. Window collisions are poorly understood as threats by birds that evolved in open tundra. Starvation occurs when owls cannot locate adequate prey in agricultural and suburban landscapes. Wildlife rehabilitators treating irruption owls report that starvation and trauma are the leading causes of admission.