Nighthawk migration is at its peak in late August. Sometimes you can see thousands of nighthawks in one evening. The birds leave northern Wisconsin early to avoid the early frosts that kill the flying insects they eat. They winter in southern South America, making their migratory journey one of the longest for North American birds. Despite their name, nighthawks are most active at dawn and dusk. You can see them flying over open fields and along roads, twisting and turning as they try to capture insects in flight.