The timing of the whitetail rut varies across the map because the ideal time for fawns to be born varies with latitude and other factors. But the external clue that deer rely on everywhere to trigger estrus in does is photoperiod: the changing length of daylight over the course of the year. The moon and weather vary too much to be reliable clocks. Only photoperiod is a fail-safe trigger. #deer #deerscience #whitetails #deerhunting #nationaldeerassociation | National Deer Association