This is important because as you know, the longest day of the year is June 21 – the summer solstice. And the shortest day is December 21st, the winter solstice – introducing the concept of photoperiodism. Simply put, photoperiodism is how living organisms react to the varying lengths of dark periods throughout the seasons of Earth’s orbit.

You’ve probably heard on the internet forums, that the rut is impacted by cold weather. You’ve probably also heard that this is both correct, but also mostly wrong. And that photoperiodism is what triggers the rut from year to year (the cold just makes for suitable conditions for increased rut activity).

(If you want to learn more about photoperiodism, GoHunt has a good article.)

Here’s how it works. As light enters the eye ball and is interpreted in the occipital lobe of the brain it affects more than just vision. As the available light fades in the environment, the pineal gland becomes active (synthesizing melatonin) and acts on the pituitary to release increased sex hormones needed for male and female readiness/eagerness to breed. The buildup of sex hormones in the blood is a slow process occurring over the course of weeks – and also affects other animal behavior changes and biological processes (such as antler growth).