The Hunter's Moon rises: How lunar phases impact deer movement, breeding

Oak Duke

Fri, September 15, 2023 

One of the most popular celestial events, the Harvest Moon, will occur in late September, on the 29th this year as a Super Moon, rising full one week after the Autumnal Equinox on Sept. 23, 2023.

A Super Moon is when the moon is closest to the earth when full in its monthly trip around the earth. Since the moon’s orbit is elliptical, sometimes it is further away and appears slightly smaller.

This year the moon will appear larger and therefore brighter as it hangs in the evening sky, rising just past sunset.

Whitetail deer and other animals, what researchers term "short day breeders" such as sheep and elk, and even chickens, turkeys and sea turtles, along with fish such as the Grunion, are all especially sensitive to changes in daylight.

Scientists call this phenomena photoperiodism.

Poets, songwriters, astrologers, dreamers, mystics, and lovers … not to mention scary story tellers down through the ages have waxed eloquent about the magical qualities of moonlight, calling light from the moon moonbeams, or light from the silvery moon.

Even the words lunacy or loony (comes from luna, meaning moon) are derived from perceived effects of basking in moonlight.

But science shows us that moonlight is simply reflected light from the sun as the moon acts like an immense mirror. The moon does not generate any light of its own.

The length of days determines the amount of light any specific location on the earth receives augmented by moonlight (reflected sunlight) at any given time.

Bachelor bucks, still in velvet, in early September.

Certain species of animals have their biorhythms more greatly affected by photoperiodism and more easily measured than others.

The Harvest Moon is particularly significant because it is always named as the Full Moon that is closest to the Autumn Equinox, one of two days each year when daylight and the darkness of nighttime are of equal length. The other is the Vernal Equinox, which occurs in the spring, in March.

The Harvest Moon acts like a "set trigger" on a gun, especially priming whitetails in the Northeast and the Midwest for the upcoming peak of the rut, or breeding time, about one month away.

This year, the rut is timed for its first major flurry just prior to Halloween, under the next Full Moon, Oct. 28 2023.

More: Here's when deer hunters can take advantage of the first rut this fall

Sheep breeders and deer farmers are very aware of the effect of melatonin on the timing of the breeding cycle of their respective animals.

For instance, in order to have all their ewes drop their lambs in the spring at the same time, melatonin implants are marketed and used as a manmade "set trigger" like the Harvest Moon is to wild deer.

Melatonin is a very complex hormone found in many animals and plants. It helps set the circadian rhythms, or life cycle responses such as reproduction, sleep, and blood flow. A small gland in the brain behind the optic nerve called the pineal gland generates melatonin which actually represses the breeding impulse in short-day breeders like deer and sheep.

When deer or sheep farmers withdraw the previously placed melatonin implants, the hormone dissipates from the ewe, or in the case of farm raised deer, doe.

Breeding can and then does take place.

The bright Harvest Moon acts in an analogous way as the melatonin implants or CIDRs (Controlled Internal Drug Release) used by the deer and sheep farmers, as light stimulates melatonin flow.

But as the moon begins to quickly wane, the short days and ever-increasing darkness help the dissipation of melatonin in wild whitetails, whose eyes have been shown by researchers to be 1,000 times more sensitive to light than ours.

A buck diligently digging up a scrape under August's Full Moon.

Much research is being done on another tiny but important hormone regulatory gland, the Suprachiasmatic Nucleus (perfectly positioned on the Optic nerve chiasm) that through the influence of light it governs the flow of melatonin created in the pineal gland.

Whitetails, to some degree, have their biological clocks set by this conjunction of the Harvest Moon and the Autumn equinox.

And one month later, the annual whitetail rut will kick into gear with the onset of the Hunter’s Moon.

Is it any wonder that the October full moon, just before Halloween this year, is called "The Hunter's Moon?"

— Oak Duke writes a weekly column.

This article originally appeared on The Evening Tribune: Lunar phases impact deer movement, breeding. What to expect this fall