Deer Defense Shield: Same Senses, Different Reactions

posted on August 25, 2015

One would think you’ve seen every possible move whitetails can make after hunting the same treestand on opening day for 30-plus years.

You know where they usually appear, where they usually disappear and where they’ll usually turn, pause or change speeds along the way. After all, you’ve seen deer alone, deer in pairs, deer in family units, and every combination of ages, gender and group sizes. You learn from each encounter, and from each mistake or success that follows.

Even so, each time you anticipate a deer’s next move and confidently counter it with a practiced response, you’re not shocked when you must lower your rifle in futility. Sure, we improve and react ever more efficiently each year, but just when you quit making mistakes of inexperience, you start making mistakes of false assumptions. Maybe that’s because no matter how much we learn about the physiological wonders of a deer’s eyes, ears and nose, the less certain we are about how and why they’ll respond to what they see, hear and smell.

If it’s any consolation, even the nation’s top wildlife professors and graduate students simply shrug when asked to explain the hows and whys of deer behavior. For example, professor Karl Miller at the University of Georgia has no problem identifying a deer’s three basic motivations in life: 1) “What’s for lunch?”; 2) “How do I keep from becoming lunch?”; 3) “Assuming I address the first two questions, how do I make more of me?”

But even though those three forces infuse every whitetail, and every whitetail carries similar defense systems, Miller concedes this: Few whitetails respond similarly and predictably in fulfilling their living requirements.

Perhaps nothing reinforces that point better than scientific research over the past 60 years. No matter how much biologists learn about the whitetail’s anatomy, genetics, food preferences, habitat requirements, home ranges and travel patterns, the less they know for certain how and why individual deer balance the risks they take to acquire life-giving resources.

Best Breeding Tactics?
In fact, it’s even hard to prove how age and experience affect whitetail behavior. Although researchers have documented that adult does typically choose better fawning sites than do yearling does, it’s tougher to prove that experience teaches adult bucks how to best find breeding partners each fall. One man who documented those challenges is Clint McCoy, who used GPS-equipped collars to track 37 bucks of varying ages during his graduate-student days at Auburn University.

“Yearling bucks and older bucks cover about the same amount of ground each day during the rut, but the way they cover ground is different,” McCoy said. “Yearlings tend to concentrate their movements in a smaller area, but they still move about the same distances if not farther than older bucks. The scientific term for their routes is ‘tortuous.’ Adult bucks are less tortuous in their movements than yearlings during the peak rut and especially post-rut. They’ll range farther on straighter, more ‘linear’ routes, presumably because they know where to find females. That seems to be especially true in the post-rut when fewer females are available. The mature bucks go hither and yon to find those last few receptive does.”

It’s a mistake, however, to assume mature bucks adapted this approach to ensure more breeding opportunities for themselves. Recent DNA research has found that 11/2-year-old bucks sire 11 to 32 percent of fawns, and an Auburn University study found that nubby bucks—6-month-old bucks—sire up to 5 percent of fawns in a given year.

“Our hypothesis is that yearlings have a greater chance of securing breeding opportunities by hanging around known female groups, and getting lucky by being the only stud on the block when a doe becomes receptive,” McCoy said. One of his collared yearlings was especially thorough, relentlessly combing a 70-acre piece of land for 24 hours.

Safe Travels?
It’s also a mistake to think the older bucks’ seeking behaviors promise a safer way to circulate their genes. For one thing, not all mature bucks make longer, more linear movements when breeding. Some seldom stray from their home area. Again, each deer is an individual with unique traits that are independent of its age and experience.

“You cannot expect every deer to act the same,” Miller noted, citing a Louisiana study in which 25 GPS-carrying bucks had similar home-range sizes and travel patterns until the rut. As the rut kicked in, their travel patterns varied wildly.

“It looked like spaghetti when you plotted everything on a graph,” Miller said. “Some increased their movements and got dead real quick. Others increased their movements but decreased their home range, and stayed alive; and some increased their home range but decreased their movements.”

Miller said one of the more fascinating studies he’s seen on buck activity was conducted by Aaron Foley at Texas A&M University. Foley categorized bucks by three categories: Resident bucks move constantly in a concentrated area, route runners take daily or every-other-day jaunts and loops over larger areas, and nomads take overnight trips miles outside their home area.

Miller likened these different routines to the singles strategies of different men. “One guy goes to the same bar every night looking for a pick-up, while another guy cruises all the neighborhood bars, and yet another guy goes to Vegas,” Miller said. “Which one has the riskier behavior? They all have their risks, and each one involves a different strategy for achieving the same goal.”

Outside Forces
So far, of course, we haven’t factored in outside forces hunters often use to explain deer behavior. How much influence, for example, do “solunar” and lunar forces have on deer movement?

Wildlife scientists apparently don’t deem solunar tables worthy of study. Miller could find only one study, done during the 1980s, that examined whether various combinations of tides, sunrise and sunset times can predict minor and major daily feeding times for fish and wildlife. The study found neither solunar table it examined accurately predicted deer activity.

“Deer have fairly consistent activity patterns, in that they move at dawn and dusk for the most part,” Miller said. “But solunar tables show them moving more heavily at different times of the day, and we know that simply isn’t true. Deer patterns will always relate primarily to food, predation and reproduction. And every study I know of except one shows deer-movement activities concentrating around sunrise and sunset. And contrary to what many people think, nocturnal activity is not built into their DNA. If they aren’t being hunted, they’ll often move in daylight. And if they’re hunted at night, they’ll increase their daytime activity.”

Night hunting? Miller said Florida researchers found that deer became increasingly diurnal in areas with panthers, presumably because panthers are nocturnal predators. “Deer in southern Florida are moving less at night to lower their risks of becoming panther food,” Miller said. “They’re moving more in daylight. They adapted to constant, chronic predation, so it’s not hardwired in their DNA to move at night. Yes, deer are well-equipped for nocturnal activity, but they understand risk and how best to avoid it.”

Lunar Factors
Miller isn’t so quick to dismiss the moon’s impacts on deer activity, but notes that most researchers have found no relation between moon phases and deer activity. Meanwhile, when hunters are polled, 75 percent typically say moon phases have at least some impact, and only 25 percent say it doesn’t. Why such enduring faith in lunar impacts on deer behavior despite the skeptical scientists? Miller doesn’t discount hunters’ observations—at least not yet.

“My issue is that in every study done to date, the research has been done wrong, even the projects I’ve worked on,” Miller said. “The trouble is that all full moons are not created equal. They all differ in the amount of light they deliver at night, depending on their location overhead, how far up they are from the horizon, and how far they are from Earth in their orbit. When the moon is closest in its orbit, its perigee, it’s 30 percent brighter than when it’s farthest away, in its apogee. And whether it’s a new moon or full moon, when they’re directly overhead, they have the same effect on gravity.”

All that variability in nighttime brightness, even without the complications of clouds, makes it difficult to pin down cause-and-effect impacts on deer movements. Even so, some research—flawed as it might be—going back to the 1950s found deer to be more active during bright moonlight. If true, it likely relates to their desires to find food and not become food.

More recently, Marcus Lashley, a graduate student at North Carolina State, studied thousands of trail-cam photos of feeding deer, and found that deer appeared less vigilant when feeding in bright moonlight. “They probably felt safer because they could more easily watch for potential predators,” Miller said. “It would make sense that when they’re more active at night that they’d move less during the day.”

As a result, Miller is now working on a two- to three-year research project using 300 trail cameras and light meters to detect the amount of luminescence. By measuring how nighttime light varies by moon phase, the researchers hope to detect impacts on deer activity.

Food Patterns
Even though lunar impacts on deer activity remain debatable among researchers, no one disputes that acorns, crops and other food sources regularly change deer patterns. Sometimes deer even shift or expand their home range to remain near a convenient, nutritious food source. Studies in South Carolina and Georgia, however, indicate it’s possible to make food so concentrated and convenient through baiting that deer become especially tough to kill.

Charles Ruth, deer project supervisor for South Carolina’s Department of Natural Resources, reported in 2008 that even though deer densities were lower in the state’s unbaited piedmont area, its hunters enjoy better hunting. Specifically, they kill more does and bucks with less time in the stand. Compared to the coastal plain, where baiting is legal, piedmont hunters were taking: 28 percent more deer per square mile; 35 percent more does per square mile; and 7 percent more bucks per square mile. Further, they accomplished it with 18 percent fewer man-days of hunting effort, and 2 percent fewer man-days per deer harvested.

Ruth believes deer become “fat and happy” when baiting evolves into prolonged supplemental feeding. With bellies forever full, deer are less motivated to move during daylight. In fact, Ruth’s research found whitetails visited deer-feeding areas in the coastal plain on a 25-to-1 nighttime-daytime ratio.

Miller said recent research in Georgia, where baiting was recently legalized, also showed deer spent more time at bait sites, but mainly at night. They then move into cover about 100 to 200 yards away during daylight to bed. That pattern continues until the rut.

“That buck is essentially un-killable in September, but then his home range explodes in November, and he’s not thinking about food anymore,” Miller said. “So either way, baiting is really not increasing his availability for harvest.”

In other words, even when we manage to make deer more uniformly predictable, they still don’t make themselves vulnerable. As a result, hunting whitetails remains challenging, no matter how much we think we know about deer.

Mark Conner, a wildlife biologist who manages Chesapeake Farms in Maryland, has overseen several buck-movement studies with graduate students. He put it this way: “There’s no silver bullet to predicting deer movements. It always comes down to finding places bucks like to be, which is usually inside the woods. The longer you’re on stand, the better your chances of seeing that buck.”

Miller agrees. “A deer is not a deer is not a deer. Each deer is different,” he said. “That’s why they’re so frustrating and challenging to hunt. Just as every person has a unique personality, every deer has a unique ‘deer-ality.’ If all deer acted the same way to every stimuli and motivation, they’d be easy for every hunter and four-legged predator to pattern and kill.

“What makes whitetails a great game animal—the most successful deer species in the world—is their incredible flexibility, adaptability and unpredictability.”


Mature bucks travel differently during the rut than 11/2-year olds. In an Auburn University study, GPS-collared bucks roamed widely in “linear” routes (blue line) to find does; youngsters covered smaller areas in “tortuous” routes (yellow line).


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