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Lull to Chaos:


Pre-Rut - what changes in deer behavior should hunters be most alert to and how can they take advantage of it?


October 01, 2012
White-tailed deer are short-day breeders; they breed in autumn when day length (photoperiod) is decreasing. It is this autumn decrease in the amount of daylight that triggers sharp seasonal changes in deer physiology, behavior, and nutritional requirements.

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While scraping behavior among whitetail bucks is done instinctively, it is a trait that improves with practice and experience. Robert Peltz photo
The whitetail's breeding window is narrow in the North, but widens southward until breeding takes place year-round near the equator. As a result, variations in commencement and duration of the rut can be expected from North to South.

Hunters commonly refer to the period immediately preceding breeding as the "pre-rut" a unique period when deer behavior can change overnight, requiring equally unique and versatile hunting tactics.

Obviously, pre-rut terminates when breeding starts. But when does it start? How does deer behavior change during the course of the pre-rut? And, more importantly, precisely what exact changes take place in deer behavior that hunters should be alert to and can take advantage of?

Differing Views

A search of the scientific literature reveals a scarcity of reference to the pre-rut period and virtually no summary of events involved. At least one reference, from Texas, suggests the pre-rut commences 4 to 6 weeks before the first does breed.

Even deer experts tend to vary in their views concerning the pre-rut. For example, in a recent Deer & Deer Hunting article Charles Alsheimer discussed in detail the so-called "September lull, October lull or pre-rut lull" when bucks seem to be especially inactive, secretive and difficult to hunt.

Conversely, when I quizzed noted deer researcher Karl Miller regarding his interpretation of the pre-rut, he dwelled upon the two week period immediately before the first does breed.

This is when something -- presumably inherent physiological changes -- takes place that literally causes an explosion in deer activity like at no other time during the year.

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“Silent ovulation.” when the female shows histological and physiological signs of estrus, including ovulation, but not the mating response, or psychological heat.

Based upon northern research experience, I admittedly have my own biased views concerning the whitetail pre-rut. Here in the Upper Peninsula of Michigan winter weather dictates seasonal changes in deer behavior. It seems whitetails are either recovering from the winter season, enduring it, or preparing for the next winter. There is no room for renegade deer behavior based on fluctuations in moon phase, temperature, precipitation, or any other such factor that might fluctuate wildly and/or unpredictably from one year to the next. If whitetails are to survive in this precarious environment, they must follow their genetically selected plan, and behave accordingly.

Be that as it may, here's the way I see it.

Commencement

of Pre-rut

One can argue as to when the pre-rut starts, because whitetails exhibit a host of physiological changes -- and resultant behavioral changes -- at this time of year. Depending upon the region, some of these changes can be subtle and difficult to identify; they can also be influenced by environmental (i.e., temperature, precipitation, etc.) or social factors (i.e., herd density, sex-age, etc.). Hence, pinpointing commencement of the pre-rut can be arguable.

Rising levels of the male sex hormone testosterone lead to antler maturation, velvet stripping, and striking changes in buck behavior. In my view, the timing of this process among mature bucks signals commencement of the pre-rut. Although velvet shedding dates vary among bucks, depending upon their age and health status (i.e., young and poorly fed bucks tend to shed late), some mature individuals on Northern range always shed antler velvet about September 1, annually -- some even a few days earlier.

Typically, reproductively experienced does that failed to raise fawns the previous spring are the first to conceive, generally during the last week of October.

In my opinion, given these antler velvet shedding and conception dates, the Northern pre-rut lasts 7 to 8 weeks from the first of September until the end of October.

Social Behavior

White-tailed deer live in complex social arrangements, where such things as dominance rank and social alliances sometimes determine whether an individual deer lives or dies. Adult whitetails also exhibit sexual segregation: bucks and does live apart much of the year, but associations change with the seasons.

Separation of the adult sexes is most pronounced during the fawn-rearing period, when does with newborn exhibit territorial behavior and social isolation by driving away all other deer from the area, including other family members. Generally, this period of aggressive isolation lasts 6 to 8 weeks, depending upon herd density.

The pre-rut period is characterized by reunion of related females and their young, intermixing of the adult sexes, and intense socialization. Sparring among bucks gradually gives way to more serious push fighting and establishment of buck dominance hierarchies. Aggression among does and their yearling male offspring encourages male dispersal to new range. Young unproductive females, on the other hand, more likely become subordinate to a matriarch doe and reunite with the family group.

Such mixed gatherings, which may involve a hundred or more deer, usually take place in select open areas during evening and at night in September. Although it's generally assumed such socializing occurs chiefly in response to concentrated nutritious forage, such behavior undoubtedly serves other vitally important social functions.

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Researchers propose that primer pheromones deposited by dominant bucks -- especially during the pre-rut period -- at rubs and scrapes help synchronize reproductive cycles, bring adult does into estrus early, and suppress the aggressiveness and sex drive of young bucks. Robert Peltz photo
Openings, while maybe not absolutely essential from a behavioral standpoint, serve deer a very special purpose during the pre-rut. When interspersed throughout densely forested habitat, openings permit deer to gather, socialize, and visually communicate. Open areas void of predators serve as arenas where bucks can display, spar with one another, engage in serious fights to decide dominance, if necessary, and communicate their social status to prospective mates and competitors alike.

This habit of early pre-rut congregating makes local deer population assessment via nighttime spotlighting especially rewarding.

But remember, some deer might come a long way to join such festivities and be elsewhere a month later. By mid-October most such grouping is over; families return to their traditional haunts and bucks become solitary travelers often covering areas several square miles in size.

For the dedicated student of deer behavior, these highly observable pre-rut changes in deer behavior are fascinating to watch. However, the late October-early November deer hunter may become frustrated, wondering where that monster buck went.

Activity Levels

Normally, whitetail's exhibit two seasonal activity peaks: during times of birthing and breeding. Their lowest level of activity occurs during summer, when nutritious foods are readily available and during winter when deer are less active in order to conserve energy. During studies conducted in Lower Michigan's George Reserve, percent of daily deer activity ranged from 21 percent on Feb. 6, to 82 percent on Oct. 18.

Given the sharp changes in buck activity that take place during pre-rut, it's tempting to refer to a "lull" in deer activity during early pre-rut. In reality, the level of activity deer exhibit during September and early October is somewhat elevated as compared to that during summer. By comparison, it's the sharp rise in deer activity that takes place during late pre-rut and early rut (late October-early November) that is so outstanding.

Activity Rhythms

Whitetails tend to be corpuscular (most active around dawn and dusk). Some deer may show additional minor peaks of activity during midday and twice at night, and follow a distinct 5-peaked daily rhythm. However, the times of peak activity for individual deer might differ, depending upon age, reproductive status, general health, metabolic needs and environmental factors. As a result, individual secondary activity peaks might not be synchronized.

In the George Reserve studies, deer of either sex had similar daily activity rhythms during most months. However, during September and October, bucks were more active than does at night, and does were more active than bucks during the day. The biological significance of this is unclear, but is probably related to differences in nutritional requirements and the approaching rut. For example, some behavior, like making scrapes, is done primarily at night.

Nutrition

Like other seasonal events in the whitetail's life, the accumulation of fat is cued by photoperiod and controlled by hormones. As day length shortens, deer become more active, eat more and accumulate fat.

During the pre-rut, high energy foods such as lush forbs, soft and hard mast, and agricultural crops are favored. Understandably, such energy-rich foods tend to be concentrated, causing equally concentrated deer activity. Or, sometimes such nutritious foods may be scarce, slowing the rate of fattening and increasing feeding activity.

Autumn is a critical time for Northern whitetails. Food quality and quantity typically decrease, fawns must reach their maximum size, and deer must accumulate fat reserves for winter. Does not burdened with nursing fawns experience less overall energy drain, molt before, and gain weight faster than does with fawns. Because fawns must physically mature and fatten simultaneously, they seldom achieve their peak weight until December.

Adult bucks usually begin fattening before other deer -- in July. As a result, mature bucks often reach their peak weight by early October. They are also the first to grow their winter coat, usually in early September.

In Alabama, bucks were less frequently photographed than expected with trail-cameras during the early pre-rut. The researchers speculated that fattened adult bucks exhibit a suppression in activity during the pre-rut, possibly in anticipation of excessive energy demands associated with the breeding season.

In my studies, conducted in northern Michigan, bucks stayed longer, on average, per feeder visit in September (about 16 minutes) than at any other time during the year.

Deer living on poor quality summer-fall range may not have the luxury of a pre-rut lull in feeding activity. Likewise, those experiencing drought may have difficulty accumulating the critical amount of fat prior to the rut. Hence, regional differences in early pre-rut buck movement and feeding activity, as well as response to bait, can be expected.

Silent Ovulation

Everything abruptly changes during mid-October. Almost overnight, bucks seem to go berserk. Scraping activity escalates, and bucks won't tolerate each other as they wildly chase every doe in sight. All semblance of social order vanishes -- or so it seems -- as belligerent bucks scurry in all directions day and night, testing every doe they find.

A number of species, including whitetails, demonstrate a condition referred to as "silent ovulation." This is when the female shows histological and physiological signs of estrus, including ovulation, but not the mating response, or psychological heat. It appears to be most common in first time breeders and usually occurs about two weeks before mating.

Some researchers, including myself, believe silent estrus might mysteriously spur the whitetail's crazy behavior a couple of weeks before breeding begins -- starting about mid-October.

In other words, a doe's silent ovulation might emit pheromones that alert and excite bucks to her pending condition, but she won't be in the mood to mate and will flee the bucks' advances.

It takes little imagination to envision the havoc and favorable hunting conditions -- that would result if several (pubertal) does entered this attractive, but elusive, state at the same time.

Signposting

With a forest-dwelling animal like the whitetail, glandular secretions and scent-marking, referred to as chemical signals, play an important role in communication -- especially prior to the rut.

These signposts are more popularly referred to as "buck rubs" and "scrapes". Although rubs are made with the antlers, they are also probably marked with secretions from the buck's forehead glands. Scrapes are pawed areas in the soil which include urine deposits as well as scent-marking of overhead tree branches probably with secretions from the forehead, preorbital, and nasal glands as well as saliva.

Most signposting is done by mature bucks, presumably to advertise their dominance, individual identity, and other information of social importance. Researchers Larry Marchinton and Karl Miller propose that primer pheromones deposited by dominant bucks -- especially during the pre-rut period -- at rubs and scrapes help synchronize reproductive cycles, bring adult does into estrus early, and suppress the aggressiveness and sex drive of young bucks.

Compared to older bucks, yearling bucks are more delayed physiologically and psychologically, in entering rut condition. Most yearlings are generally delayed a week or two in shedding antler velvet and never do achieve the sex hormone "highs" that stimulate mature bucks.

As a result, these younger bucks, on average, only make about one-half as many rubs and 15 percent as many scrapes as older bucks. Since yearlings make very few rubs during the early pre-rut, an abundance of antler rubs during September and early October invariably reveal the presence of a dominant buck 3.5 years of age or older.

While scraping behavior among whitetail bucks is done instinctively, it is a trait that improves with practice and experience. Mature bucks tend to scent-mark overhead limbs year­ round, but normally do not develop full-fledged scrapes by pawing the ground beneath the limbs until early September. Yearling bucks tend to commence scraping about 6 weeks later than mature bucks.

The overhead limb is an essential part of the scrape. Without it, there is no scrape. If you take away the limb, the most traditional, diligently pawed scrape will disappear. On the other hand, if you add a limb in the right location, bucks will paw the turf beneath it with dedication, forming a new scrape where none had ever existed -- without further human doctoring of the site.

Regardless of their age, whitetail bucks exhibit peak scraping activity at about the time the first does breed -- during the last week of October or first week of November. The important thing to note is that most scraping activity (50 to 60 percent) occurs before the first doe breeds, and the frequency of new scrapes declines sharply thereafter.

On average, prime-age bucks only freshen and maintain slightly more than half of the scrapes they make, versus about a 40 percent retreatment rate for yearling bucks. Due to their more frequent repawing of scrapes, prime-age bucks also tend to make larger scrapes than do younger bucks.

Conclusions

Antler velvet stripping, starting about the first of September, signals start of a 7 to 8 week chaotic period commonly referred to as the whitetail pre-rut. Although initially rather mild mannered and not very active, bucks simply go berserk in mid-October and for several weeks are more active than they are at any other time during the year.

All things considered, if I had my druthers, l would be hunting during the last week of October and the first week of November, annually -- when bucks are active about 80 percent of the time.

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