I tend to agree on the photoperiodism, Gary... But Charlie says that the Pineal Gland is the real controller of the estrous cycle, and it's triggered by exposure to moonlight.
At some point in autumn, the amount of sunlight decreases enough to reset the whitetail's reproductive clock, thus placing the breeding season in November, December and January in the Northern Hemisphere. Once a doe's reproductive cycle is reset by a specific amount of daylight, her estrous cycle is ready to be cued by moonlight, which provides a bright light stimulus to the pineal gland several nights in a row each lunar month. Then, the rapid decrease in lunar brightness during the moon's third quarter triggers hormonal production by the pineal gland. Physiological changes prompted by the pineal gland culminate in ovulation and estrus.
I, for one, would like to read whatever scientific literature he's relying on - with regard to the Pineal Gland - as it relates to estrous and moonlight. I have a hard time swallowing that.
If light at nighttime really triggers the estrous cycle - then couldn't a doe be thrown into estrus by bedding too close to a dusk-to-dawn light? What's so special about moonlight? How does this Pineal Gland work?