With bear and goose seasons underway, thoughts wander ahead, particularly to deer season.

And with bucks starting to rub the velvet off their antlers, conjecture is already running rampant about when the rut will occur this year. It’s little wonder deer hunters are fascinated by this brief window of opportunity; it’s often the only time super-wary older bucks drop their guard and wander around during daylight hours. Knowing when that will happen could be pretty handy, particularly for those folks who want to schedule their days off to coincide.

Theories abound on what triggers the rut. Some say it’s the timing of the full moon. Others claim it takes a good hard frost or a cold front. Then there are more far-fetched notions like the width of bands on a woolly bear caterpillar or the timing of apple or acorn drops.

Well, folks, I’m about to disclose a trade secret on how you can reliably predict the rut not just this year but every year.

In the south, rut timing gets pretty messy; it’s all over the calendar, even within a particular state. As you move north it becomes much more defined, primarily because there are selective pressures at work.

The presence of white-tailed deer on the North American continent dates to at least the end of the Miocene epoch, about 5 million years ago. Since then, natural selection has directed deer biology and behavior in a certain direction, one that provides the greatest chance for survival. One of the largest selective pressures in northern regions is climate and associated food availability.

Deer mate in the fall and give birth in the spring. If mating occurs too early, fawns will be born early, before there’s sufficient nutrition for nursing to properly nourish newborns. If it occurs too late, fawns won’t achieve sufficient growth to survive their first winter.

Not every year is the same and like all species, deer constantly challenge selective pressures, looking for a better way to ensure the survival of their offspring and perpetuating their genetic material. There are always a few early-born fawns and in years when spring comes early, there’s ample food for nursing mothers. And some years winter lingers and those outliers are culled.

The same applies to winter, where smaller, late-born fawns may survive a delayed or mild winter but not a severe one. There are always exceptions but over 5 million years nature has honed the species so most adult does will have the potential to breed during a fairly narrow window – approximately 10 days. Hunters often call this period as the rut or peak rut. Biologists refer to it as peak breeding because the rut actually involves all behavior associated with breeding, including the scraping and rubbing that can precede peak breeding by a month or more.

Knowing when the rut occurs is also important from a wildlife management perspective; the relationship between hunting seasons and the rut can have a potentially significant impact on hunting-related mortality. For example, research on nationwide trophy buck harvests showed states that consistently had the highest number of mature trophy bucks in their harvests had three things in common. They have short firearms seasons that don’t coincide with the rut and firearms hunting is limited to shotguns. Allow rifle hunting during the rut and you’ll kill more deer, particularly bucks. If your deer herd is healthy and you’re not worried about hunters being able to harvest more older bucks, that may not be an issue.

So biologists have studied deer breeding chronology for decades. They have developed several reliable methods for measuring when peak breeding occurs, and now have a fairly accurate record. I recently queried deer biologists from all the northern states where whitetails live and asked when peak breeding occurred in their state. Answers varied slightly from one state to another but every biologist or manager noted one commonality. Regardless of the moon, weather, climate variations or other variables for that matter, peak breeding occurred at the same time every year. Let me restate that in case you missed it. According to all the empirical data currently available, peak breeding, or what hunters call the rut, occurs at the same time every year. You can mark it on your calendar just like Thanksgiving and Christmas; that is, once you’ve determined exactly when that happens in your neck of the woods.

Bob Humphrey is a freelance writer, registered Maine guide and certified wildlife biologist who lives in Pownal. He can be reached at:

[email protected]