Science Behind Deer Activity
Understanding reasons behind movements has hunt implications
This is the third in a series of articles looking into the science behind whitetail deer
Read Part I: Science Of Deer Vision
Read Part II: The Science of Antlers
One of the most important components of successful whitetail hunting is patterning animal movements. The hunter must determine when deer are most active and how they're using different habitat types at different times.
Understanding deer activity starts by looking into home range, defined as the area used by a deer during the normal daily activities of eating, mating and raising young. Whitetail home ranges vary drastically based on many factors and can range from 250 to 2,500 acres.
Typically, areas with a consistent mix of food, cover and water lead to smaller home ranges. Deer are faithful to seasonal home ranges across the years, and females have a particular affinity for traditional home ranges, with does often using the same or adjacent areas as their mothers or other female relatives.
Most bucks disperse from their home range of birth and establish new home ranges, but afterward they show fidelity to the new home range.
Home range can change seasonally as a result of habitat availability. For example, one Nebraska study showed a shift in the center of a whitetail's home range of 174 meters closer to corn fields when corn was in the tasseling and silking stage, and a shift 157 meters away from the corn field after harvest, when range size increased by almost a third.
Within home ranges, many factors influence whitetail activity, including time of day, an animal's age and sex, the time of year and the weather. Still, numerous studies - and the observations of countless hunters over the ages - show that whitetail activity generally peaks at dawn and dusk.
Sunset seems to be the period of greatest activity, while times of lowest activity take place during the predawn early morning, late morning and late evening after sunset. Some studies have reported a distinct dawn-and-dusk pattern during some seasons and a lack of any pattern - or a shift to a single peak - in other seasons. Other evidence points to minor peaks at midday and midnight.
It shouldn't be a surprise that all these generalizations about activity don't always hold true, and that activity patterns vary widely within individual animals and also change as a result of factors such as predators, food availability and reproduction.
Speaking of reproduction, a whitetail's sex affects its daily activity patterns. For instance, although daily patterns usually are similar between bucks and does, patterns change in early autumn, when bucks are more active than does at night, and does are more active than bucks during daytime hours.
Research also illustrates distinct seasonal differences between the sexes as a result of herd social structure, reproductive behavior, gestation and lactation activities and region. On average, females are active 1 1/2 hours per day longer than males between January and July, and they also spend more time in heavy cover.
Demands of pregnancy and lactation require a high-quality diet that necessitates an increase in foraging activities. In northern areas, deer move less during winter and shift to more daytime activity as a response to lower temperatures. In southern Texas, the greatest activity occurs in January and again in September-October, while in southern Michigan, the greatest activity takes place during May and October, with lowest activity during midwinter.
Although it's no secret that weather plays a role in deer activity, research shows that temperature may have the biggest impact across all four seasons. In one study, deer observations during spotlight counts were directly related to temperature and negatively correlated with cloud cover, precipitation and dew.
In a Michigan study, deer activity rates during spring, summer and autumn were greatest between 50 degrees and 61 degrees, with activity rates declining in direct response to temperatures above or below that range. Responses to temperature are probably different in more southerly latitudes.
In an Oklahoma study, bucks during winter moved more when temperatures were lowest, while females during summer moved greater distances when temperatures were normal to high and less when temperatures were coolest.
Although it's considered an important factor among hunters, wind seems to have very little effect on whitetail activity. It's important to note, however, that deer do tend to seek out sheltered areas that reduce wind speed on blustery days (this is especially true during winter).
Movement in response to precipitation is unpredictable, although it has been reported that deer are often less active during heavy rainfall or during snowstorms with high wind.
The moon's effect on deer movements is a common subject around deer camps and coffee shops where hunters gather, and unfortunately, many questions remain.
A pair of research projects from the 1970s pointed to some potential effects caused by the moon, with one study reporting increased movements during both day and night around the time of the full moon, and the other observing increased use of open habitats on moonlit nights. Most research, however, has found little or no effect of moon phase or moonlight on whitetail activity.
The breeding season can affect activity, which likely isn't any surprise to deer hunters. But there's science to back up what we've all seen through the years. This particular change in activity typically manifests in the form of unusual short-term movements outside of a deer's home range. Two studies reported that more than half of their research bucks made excursions outside their home ranges during breeding season, movements that were assumed to be the result of either a search for receptive females or a buck's tending to estrous does as the does moved back to their core areas.
A final facet of deer movement that can't be overlooked is dispersal. Dispersal is defined as the permanent movement from home range of birth to a new home range. It's a common behavior of many vertebrates and is likely a mechanism to avoid inbreeding.
As mentioned previously, does tend to stay in or near where they were born, while young bucks typically move out of their birth area. Radio telemetry has shown that most dispersal takes place among yearling bucks. Other research has shown dispersal rates in bucks as high as 70 percent.
The nature of a whitetail's habitat plays a part in the distance of dispersal, with bucks moving farther from their birthplace range in open or fragmented habitats. For example, bucks in Midwestern U.S. agricultural areas have been shown to disperse more than 25 miles from their original range.
Although it seems obvious that whitetails, like many mammals, are hard-wired to disperse so they enhance genetic diversity, we know less about the actual behavioral stimulus that triggers dispersal. Because there are differences in the timing of dispersal, two hypotheses have emerged.
Social pressure from other bucks or competition for mates may be one cue for young bucks to disperse, a scenario that is evidenced by dispersal that takes place prior to the autumn rut. Social pressure from female relatives may represent another dispersal cue, in which case the dispersal takes place during springtime.
It's not breaking news that deer spend a lot of time on the move. But understanding the reasons behind their movements can increase our chances of being in the right place at the right time to make sure they cross our paths.
For video of Michael Waddell's study of a whitetail, click here.
Next: Science behing hunting pressure
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