The rut: Deer grow single-minded, goofy for the once-yearly breeding cycle

As the peak of rut approaches, adult bucks tend to travel more — often in daylight hours — scenting for hints of approaching estrus status in does.

Single-minded deer turn goofy for the yearly breeding cycle

Hunters’ fondest dream and automobile insurance agents’ recurring nightmare, the annual deer rut is cranking up.

The occasion is the climax of the yearly reproductive period of white-tailed deer. It is largely a one-and-done thing for deer, although the entire process is much longer than people recognize.

The breeding cycle actually begins when the hormonal levels of adult buck deer jump in late summer, usually around the end of August. That coincides with the bucks’ fast-growing antlers attaining full growth and the softer tissues beneath the velvet covering hardening into bone. The velvet is shed and each buck sports the set of new antlers in time for status and weaponry of the competitive reproductive period.

The breeding cycle doesn’t end until mid-winter to very early spring, when the testosterone level of each buck effectively drops like a rock. That’s the cause of each buck’s antlers doing likewise. When a buck’s bony rack is shed, that is a sign that he is hormonally incapable of breeding. He stays that way until the next antlers are fully developed months later.

Adult female deer, however, have a much narrower reproductive period. Each breeding-ripe doe comes into estrus, ready for insemination, for about 24 hours. Should a doe come into estrus and fail to be impregnated during this short time, nature lets her repeat the physiological event 28 days later. In theory, there is supposed to be a third estrus round possible 28 days after that.

In practice among wild deer populations, there is little need even for a secondary estrus period. Does put out a scent that cruising bucks identify when the estrus flower is approaching its time to bloom. Bucks are driven to seek does during this time when most are approaching estrus, traveling with their noses in the lead, sniffing out possible mates.

In most cases, where there is a doe near the breeding phase, a buck or a few bucks will find the developing prize. It is more common for a doe to be the object of competition — posturing, stare-downs or all-out fighting — than to be without any suitor.

There are individual differences in does, some entering estrus sooner than other. But within a handful of days around mid-November, perhaps as many as 80% of adult does in a wild population of deer at this latitude are bred. (In the Deep South, climatic differences shift the breeding period later and allow it to occur over a longer time.)

Some of this baby-making phenomenon among deer hits its craziest stretch before the actual breeding time. When significant numbers of does are approaching estrus but still not ready for breeding, bucks tend to go a little bonkers. They can sense the magic hours approaching, and instincts to breed send them on a mission.

Bucks begin traveling outside their normal home ranges, sometimes miles beyond their typical turf, in search of ripened females. Scenting trails for whiffs of sexy does, they cruise other deer habitats in hopes of quick dates and purposeful sex. During this time, does typically will flee the would-be suitors.

Deer activity increases overall during this pre-breeding phase. It seems to increase dramatically to people and especially deer hunters because bucks begin traveling much more during hours of daylight when they are far more easily observed.

Hunters love this period because their chances to encounter older, larger and normally more wary bucks grow significantly. Many mature bucks hardly stir in daylight much of the year, but come this period, they may cruise nearly around the clock. In doing so, they also abandon a bit of their caution as the reproductive drive pushes them.

While the entire chain of events takes weeks and months, people like hunters who are most interested in deer tend to identify the rut as that period right before the chief breeding period. That is the time when the most deer movement is sighted, that resulting from the most seeking and chasing of does by anxious bucks.

The internal signals and physical changes that drive deer in this annual pandemonium are mostly driven by the photoperiod, the daily length of sunlight. Contributing factors that might speed or slow the process could be temperature or other weather signals like light-filtering cloud cover.

Most hunters come to favor frosty temperatures and perhaps light winds, expecting the most deer activity under such conditions. But note that the Kentucky Department of Fish & Wildlife Resources schedules the opening of the state’s firearms deer hunting season to begin on the second Saturday of November each year, confident that the next several days will catch the peak of rut-related activity.

Some years, unseasonably warm weather seems to muffle the rut. Biologists point out that warm daytime temperatures hardly eliminate deer breeding pursuits. They only shift much the activity to the hours of darkness.

With seasonally cool and somewhat unseasonably cooler temperatures associated with gloomy, cloud-cloaked days, this autumn should have deer hormones primed for some early rut-related behavior. Here at the tail end of October, we should expect to see a little more exploratory behavior from buck deer and maybe some spirited retreats by unready does.

Within a period of a couple of weeks, rut behavior should rise to a fever pitch. You might not be excited, but if you were a deer you would be.

Steve Vantreese, a freelance outdoors writer, can be contacted at outdoors @paducahsun.com.