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  • Writer's pictureChuck Adams

The Shocking Science About String Jumping

Animal reaction time, arrow speed, and shot distance can be combined to predict how likely you are to bag a critter that hears your bow. The following facts might blow your mind. (My ground breaking article from Bowhunting World Magazine reprinted by popular demand.)

If you haven’t experienced string jumping, you haven’t bowhunted very long.

I tasted this bitter pill during my first bowhunt for blacktail deer in my native state of California. I was an inexperienced teenager, but I practiced hard with my Ben Pearson Hunter recurve bow and Herter’s aluminum arrows. Within 30 yards, I naively believed that bucks would be in serious trouble.

I got my first dose of reality on the second day of deer season. I tiptoed close to a handsome forked horn buck as he chewed on a bush. I was hyped up, but the arrow came back smoothly and the shot felt good. To my horror, the shaft smacked empty dirt at least two feet behind the deer. That animal crouched and leaped ahead so fast I did not even see the move.

At first I thought I had blown the shot. Then I realized my arrow was buried in about the right place. It was the first of many sad lessons learned about shooting a bow at quick-footed critters.

The late, great Fred Bear told me many years ago that it took him three years to bow-bag his first deer. At the tender age of 16, after three years of trying, I also shot my first archery buck. I felt honored to follow in the footsteps of my boyhood hero.

Those three years included dozens of mistakes, but my single biggest frustration was string jumping. Even with a new, faster and quieter Wing Thunderbird recurve bow and lighter Easton aluminum shafts, it seemed that every close-range buck ducked my arrow. Unlike blacktails in most places, California deer were small, quick, and scared to death by large populations of mountain lions, coyotes, and human hunters. My arrows were flying less than 200 fps, and deer easily hopped out of the way.

The last straw came when I decided to aim two feet in front of a 30-yard buck. The deer had me nailed, with ears cupped ahead and eyeballs boring right through me. Yet when I released, the rascal stood like a statue and watched the Bear Razorhead broadhead hit in front of his chest. Only then did he swap ends and flee.

Sweet success finally happened a few days later. A small two-point fed from a thicket at sundown. I guessed the distance at 40 yards and let fly. The deer did not move, and the arrow smashed home with a satisfying plunk. Until that instant, I had begun to doubt I would ever see my arrow hit a deer.

Contrary to common belief, a target animal almost never “ducks the arrow”. In rare cases, on ground-level hunts, a deer, antelope, elk, or other fast critter might see your hand move as you release the bowstring or catch the glint of an arrow arching through the air. This was more likely 100 years ago when Pope, Young, Compton, and other bowhunting pioneers sneaked around and shot arrows under 150 fps. Even half a century ago, bowhunters like Fred Bear almost exclusively hunted on foot and shot arrows below 200 fps. Stalking at eye level with game and shooting slow arrows increased the odds of animals seeing the shot. But today, with fast arrows and most hunting accomplished from tree stands or enclosed ground blinds, the reason animals jump is almost always sound—not sight.

I am surprised that myths and confusion still abound among bowhunters about string-jumping. Today’s age of hunts on film and precise electronic calculations should remove a lot of random speculation about the ins and outs of shooting at fast-footed game. Yet arguments still rage at archery shops and hunting camps. Can deer duck a fast arrow? How much do deer crouch to load their leg muscles? Can an arrow ever beat the sound of the bow?

The following, mind-blowing facts should help to settle questions about how and why animals manage to evade even fast-flying shafts.

First, let me tell you there is no such thing as a silent bow. Unless the wind is blowing and nearby cornstalks are rustling, a low-flying airplane is passing overhead, or rain is pounding the countryside, critters like whitetail deer WILL hear you shoot. In today’s age of aggressive cam-bows, super-light arrows, and metal-jawed release aids, even moderately hushing a shooting setup is difficult.

With rubber string silencers, brush buttons against the limbs, an arrow weighing nearly 600 grains, and a finger release, the recurves and longbows of yesteryear shot with a muted swish and thump. Yet deer inside 30 yards still registered the sound. The solid crack of a modern compound bow—even one dampened with limb cushions, string and cable silencers, and a flex-stabilizer—will be heard by every nearby animal.

In my experience and that of several deer-hunting buddies, a close-range whitetail deer will jump the bowstring at least 75-percent of the time. Pronghorn antelope hunted on foot are almost as bad, and even innately calmer species like mule deer can also come unglued if intimately threatened by the close-range sound of a bow.

All things considered, whitetails are the string-jumpiest critters on our continent. Lucky us. More archers hunt whitetails in more places than all the other 28 varieties of North American big game combined.

A deer’s string-jumping movement happens so fast that most bowhunters never see it. In many cases, archers believe they have muffed the shot when they miss or score a poor hit. Fact is, a high percentage of “bad” shots would have been perfect if the animal had simply stayed put.

Thanks to modern filmography, we now know that string-jumping animals follow a surprisingly predictable pattern. A critter hears the bow, crouches in the front end, and jumps away to avoid danger. Deer and other species often lean away from threatening sounds as they drop to load their leg muscles before they spring away. Which direction they run is anybody’s guess.

Some animal reactions to noise are mind-blowing. African impala antelope are similar in size and temperament to Texas whitetail deer, and they are chased by predators every day of their lives. It should be no surprise that they are world-class string jumpers. However, one nice impala did surprise me with his stunning attempt to dodge an arrow.

I shot the animal at 20 yards from a 20-foot tree platform, and as usual I aimed at the bottom edge of his brisket to compensate for the expected duck. The arrow sliced both lungs and lodged in the far shoulder, and the impala dropped after running 50 yards. Something seemed odd as he ran, and I realized my arrow had angled UPWARD through the antelope despite the downward shot. A quick inspection of the carcass confirmed it.

Back at the water’s edge, I found a deep dent where the antelope had dropped completely to the ground and driven his shoulder into the mud in a frantic attempt to get away. When my arrow arrived, the impala was on his side with his left ribcage toward the sky. The arrow entered low and angled upward through the chest. If I had not aimed below the chest cavity, that impala would have completely avoided my arrow.

The basic dropping, leg-loading, and lunging away of an impala, whitetail deer, and other speedsters might be predictable, but variables can cause bow-shooting trouble. An abundance of slow-motion videos of string-jumping deer are available on the Internet, and I would encourage you to watch a few so you understand what you might be up against. Some even completely relaxed deer drop their bodies all the way to the ground before the arrow arrives, and a few flop on their sides like my African impala did. Others respond with a half-crouch before running away. As mentioned before, a handful of deer do not react at all.

It seems that regional and gender variations in deer can affect string-jumping too, along with more obvious things like rutting preoccupation, bow-masking wind noise or rainfall, etc.

Here’s one example. It has been my experience that southern whitetails are jumpier then northern deer. Why this is remains a mystery, except that animals in states like Alabama and Texas are smaller and seem to be naturally more agile. Deer in the South might also be hunted harder and more tightly wired than animals in more remote places like Montana and Saskatchewan.

Similarly, a number of bowhunters I know have confirmed my belief that does are more prone to jump the string than bucks. During the rut, this makes perfect sense. Females tend to keep their wits about them while males strut around in a hormone-triggered daze. But even non-rutting whitetail bucks seem a bit less string-jumpy than females.

A seasoned bowhunter does not need slow-motion videotape to know the legendary speed with which a deer can evade an arrow. For example, western Montana offers a late-season archery bowhunt for whitetail does. I lived in the Big Sky State for several years, and took full advantage of this chance to fill the freezer with venison.

One morning, a fat doe fed toward my brush blind and quartered away at 30 yards. I scored a perfect double-lung hit. She whirled, ran the opposite direction, and collapsed. Amazingly, I shot at her right side, but the nock and fletching was sticking out the LEFT side with the broadhead buried in the right shoulder. In a few milliseconds, that deer had crouched and whirled 180 degrees before the arrow arrived! I never saw it happen.

Back then, my bow-and-arrow was slow—a touch over 200 fps—and as I’m about to discuss, that left plenty of time for the Montana doe to perform her Olympic-level evasion move.

String-jumping is a five-part process. First, the bow makes noise. Second, the noise travels to the animal. Third, the animal’s ears register the noise. Fourth, the brain processes the noise and sends a signal to the muscles. Fifth, the muscles receive the signal and react. Thanks to modern technology, the approximate timing of this process is no longer a mystery.

To understand animal reaction times, it is instructive to first consider world-class Olympic runners like Carl Lewis and Usain Bolt. Deer and humans are both mammals with similar central nervous systems, so it makes sense that physiological responses might be similar.

Reaction times for athletes in events like the 100-meter dash have been carefully studied. In recent times, loudspeakers are placed directly behind the starting blocks to prevent any lag time for sound to travel from a distant starting gun. Runners instantly hear the gun.

Carl Lewis set his 1991 100-meter World Record with a time of 9.86 seconds. He reacted in the blocks on that run .140 seconds after the gun. In other races that same year, Lewis left the blocks in as much as .166 seconds, with an overall average of about .150.

Nearly 20 years later, Usain Bolt set the new and current 100-meter World Record at the 2009 World Athletics Championships with a time of 9.58 seconds. Bolt’s start time (reaction time after the gun) was precisely .155 seconds. Lewis and Bolt are the most decorated Olympic sprinters in history, with nine gold medals apiece. Their average reaction time to the starting gun has consistently been in the neighborhood of .150 (15/100ths) of a second.

Without watching deer jump the bowstring in slow motion, it might be logical to assume an animal would react to sound on about the same timetable as a human. Average human test subjects have shown that once a sound reaches the ear, it takes about .010 seconds for the stimulus to travel to the brainstem. It then takes about .025 seconds for an impulse to pass from the brainstem to the brain’s auditory cortex. The cortex identifies the sound and sends a pulse to the muscles. On average, this takes another .05 seconds. From cortex to muscles (like a runner’s feet and legs) requires another .08 seconds. In total, average human reaction time to a sound is .165 to .20 seconds. Top male athletes might respond a bit faster, but not very much. The speed of human neural pathways is “baked in the cake” and cannot be improved upon like raw running speed can. It’s pretty constant from person to person, regardless of athletic ability.

Despite speculation about reaction times in deer versus humans, the proof is in the pudding. By reviewing videotapes frame by frame, it becomes obvious that a deer’s reaction to noise is somewhat faster than a man’s. How much faster? Based on studies I have personally conducted, it appears a whitetail buck or doe can react to a dangerous sound in about 2/3 the time it takes Carl Lewis or Usain Bolt to leave the starting blocks.

Take for example one video of a relaxed and feeding whitetail doe shot at from a measured 29 yards with an arrow traveling 300 fps. At an average fall hunting temperature (45 or 50 degrees Fahrenheit), sound travels about 1,100 feet per second. At 29 yards, the sound of the bow in the video reaches the deer in .079 seconds. The arrow has traveled slightly less than 8 yards when the sound reaches the deer. That leaves a full 21 yards of arrow travel for the doe to react and duck.

What happens next is an eye-opener. The doe begins to crouch between .17 and .18 seconds after the shot is taken, and her shoulders drop about 11 inches before the arrow sails over her back. Total arrow flight from bow to deer takes .29 seconds.

Other video reviews show similar reaction times for whitetail deer. In other words, once bow sound reaches a whitetail, it takes about .10 (1/10th) seconds for the animal to react. From there, the deer can move (drop and roll, turn, or run) about one inch per .01 (1/100th) seconds.

I’m not sure why deer can react 1/3 faster than Olympic sprinters. Perhaps prey species have simply evolved with superior neural pathways that help them avoid predators. Another reason might be that a deer’s shoulder and front-leg muscles are closer to the brain (20 to 30 inches) than an athlete’s legs and feet (50 to 65 inches). It takes more time for nerve impulses to travel between brain and legs in an athlete.

Interestingly, tests by neurophysiologists have shown that a woman’s reaction time to auditory stimulation (sounds) is about 10-percent faster than a man’s. Could that also apply to doe deer, and be the reason many bowhunters think does are more string jumpy than bucks?

Regardless of specific reasons why deer react so fast, it does not require rocket science to draw some conclusions about shooting a bow at jittery critters. At 20 yards, for example, bow sound reaches a deer in .055 seconds. If it takes the animal another .10 seconds to react, your arrow would have to be traveling just under 400 fps to reach the deer before it starts to move. At 300 fps, the deer might drop its vital chest 4 to 5 inches before the arrow arrives. With a slow arrow traveling 200 fps, a 20-yard deer in full string-jump mode could potentially drop its chest over 14 inches, or drop a more likely 10 or 12 inches and then begin lunging in an unpredictable direction.

At 25 or 30 yards, the math is more distressing. An average whitetail stands 36 to 38 inches at the shoulder, has a total front torso depth of 18 inches, and has a vital heart/lung cavity measuring 10 inches between spine and brisket. At 30 yards, bow sound reaches the deer in .08 seconds. Add a reaction time of .10 second, and a 300 fps arrow must travel another .12 seconds before it arrives on target. A deer can drop 11 or 12 inches in .12 seconds to load its muscles before leaping away. Or perhaps it drops only 8 or 10 inches and begins to swap ends or lunge ahead.

A 200 fps arrow reaches a 30-yard target in about .45 seconds. With a combined sound travel time and deer reaction time of .18 seconds, a 30-yard deer has .27 seconds to duck and run. That means the deer will probably move a combined distance of over two feet before the arrow arrives. There is no way to accurately compensate for that.

Here’s another wrinkle to think about. An arrow always slows down after it leaves your bow. How much depends on several factors, including shaft diameter and surface material, fletching size and degree of angle, arrow weight, broadhead style, and how well your bow is tuned. Most hunting arrows decelerate between 1 and 3 fps per 10 yards of forward travel. Depending on your shooting setup, this means a 30-yard deer might be able to drop an inch or two more than the foregoing calculations indicate.

Within 30 yards, my experience tells me that most whitetail deer hear the bow and react. Some react violently. Others crouch a bit or merely flinch. A few do not react at all. Fortunately, most whitetails are hunted from stands with average shots under 20 yards. This lets you manage the string-jumping risk if you know what to do.

First, since whitetails almost always hear the bow, you should shoot the fastest setup that is accurate. A 200 fps arrow will make every shot a crapshoot. At 280, 300, or 320 fps, you can aim for the heart on 20-yard whitetails (slightly above the “elbow” of the front leg) and kill them every time. If they crouch, you will score a mid to high lung hit. If they don’t, you will hit the lower chest.

At 25 or 30 yards, a fast arrow lets you aim for the bottom edge of the body and drill a deer that ducks. Here’s where experience comes into play. Will your target actually crouch or not? I rarely see northern whitetails go into full string-jump mode, so I routinely aim for the heart out to 30 yards. By contrast, in places like South Texas you can almost bet a deer will drop like a rock at the sound of your bow. If you do not aim for the lower edge of the body, your arrow might miss completely or hit above the vital lungs.

The first time I hunted South Texas, I cleanly missed two string-jumping bucks. On my third attempt, I aimed at the bottom edge of the brisket and hit the deer dead-center through both lungs from 18 yards. According to official Pope and Young Club statistics, record-size whitetails are shot closer than any other species—for good reason. Regardless of where you hunt, these animals can be difficult to hit beyond 25 or 30 yards.

Fortunately, most other types of North American big game are not as wired as whitetail deer. Large critters like elk certainly react to bow noise. Slow-motion videotape has proven that. But a bull elk has a 16-inch vital chest cavity, and his 750-pound body takes longer to move as he loads his leg muscles to run. Comparing an elk to a deer is like comparing a Japanese sumo wrestler to Usain Bolt.

Mule deer and blacktail deer are fast on their feet, and might jump if looking at you with suspicion in their eyes when you shoot. But these animals are fairly calm by nature and seldom duck like a whitetail unless the bow is loud.

Other critters like wild sheep, mountain goats, caribou, and bears are not prone to duck and run when they hear a quiet bow. I have had the good fortune to bow-bag every type of big game on our continent, and I’ve never had to aim dramatically low or worry about string jumping when after non-deer species…except for the pronghorn antelope.

The pronghorn is our fastest-footed animal, capable of running up to 60 miles per hour. By comparison, a deer maxes out at 30 miles per hour.

It is a giant risk to shoot at a running pronghorn, whitetail, or any other animal with a bow, because ground speeds, distances, uneven terrain, and other complexities make the feat impossible to pull off on purpose. Famous bowhunter and trick shot Howard Hill was legendary for hitting moving targets, and he wrote about killing Big Blue, a 5x5 Nevada mule deer, as the animal ran broadside at 60 yards. With Hill’s primitive split bamboo longbow, he had to shoot about 13 yards in front of that deer to make the hit. Yet the great Hill admitted afterward that he could not make such a shot with any regularity. Even a broadside deer running 20 yards away would be almost impossibly difficult to hit in the 10-inch vital zone with a 300 fps arrow. You would have to lead that deer close to 10 feet, or about 1-1/2 body lengths, and hope the animal did not step in a dip or jump over a bush as the arrow arrived.

Back to pronghorn antelope. Even when stationary, a pronghorn can be a string-jumping son-of-a-gun…especially under 30 yards. I have bagged more than two dozen pronghorns with a bow, and more than half of those by spot-and-stalk hunting. One that got away stands out in my mind.

“Odd Boy” had nice record-book horns, but the right one tipped oddly backward above his neck. That antelope was easy to spot in his wide-open habitat, and I stalked him almost every day for two weeks. I missed three shots in the process. That “goat” would hear my bow every time and lunge ahead before the arrow arrived. My average shot was 30 yards, and all those arrows hit several feet behind. Unlike whitetails, pronghorns are designed for horizontal speed. In my experience they don’t duck arrows—they run away from them.

At season’s end, I was tearing my hair out and Odd Boy was still alive. Like people, animals are individuals, and that antelope was a lot jumpier than most. But no matter which pronghorn I am stalking, I prefer shots between 40 and 50 yards because low bow noise does not seem to bother this species unless animals are close. If you are good enough with a bow, shots beyond 30 yards will reduce the chances of arrow ducking on most types of North American big game.

Regardless of species, you can reduce the chance of string jumping in other important ways.

First, try to mute the sound of your bow as much as possible. Limb, string, and cable silencers all help. A flexible stabilizer with rubber components also absorbs noisy bow vibration. Make sure all assembly screws and bolts on bow, sight, rest, and quiver are tight to prevent shooting rattle or buzz.

Arrow speed is important, especially on jumpy whitetail deer, but a slightly heavier shaft will absorb more bow energy and reduce game-spooking noise. For larger and less jumpy animals like elk, I prefer moderately heavy arrows for better penetration and quieter shooting.

An enclosed blind is one of the best remedies for string jumping—even on whitetail deer. A covered pit or pop-up blind holds in bow noise and greatly reduces animal reaction. Pronghorns shot from blinds near water almost never hear the bow, and neither do deer ambushed along food plots or travel corridors.

One of the most dramatic examples of this occurred on a hunt I made in Zimbabwe, Africa. The first few days, I sat on a tree platform near a waterhole. Average shots were 20 yards, and I bagged kudu, waterbuck, impala, and wildebeest with no trouble.

Meanwhile, the gray duiker gave me fits. This small, spike-horned antelope weighs less than 50 pounds and has a body only 10 inches deep. The duiker is near the bottom of the African food chain, and always approaches water with flanks twitching and legs quivering. The 6-inch chest cavity is a small enough target on a stationary duiker, but I never saw one stand still for very long from that tree stand. I missed seven duiker in a row those first few days—a situation so laughable my professional hunter (guide) began calling these little rockets “Adams Deer”!

Like whitetails, African duiker will crouch, wheel, and run at the smallest unnatural noise. My bow must have sounded like a thunder clap to those tiny ears.

Finally, I moved to an enclosed pit blind beside another waterhole. In two days, I cleanly bagged five duiker with five shots. Shooting distance was about the same, but that blind muffled the noise of my bow and made all the difference.

To combat quick-footed critters, you need to study your quarry. Never forget that some animals can react faster than Olympic runners to the sound of your bow. In whitetail country, particularly southern habitats, deer will jump your string at least ¾ of the time. Insist on a fast arrow, aim low on the chest, and limit your shots to 30 yards.

Longer shots and dead-center aims are often possible on other species, but you still need a quiet bow. Never shoot at animals on high alert, especially if staring intently your way. Critters might see you release and run, even if bow noise does not set them off.

An enclosed pit or upright blind encapsulates and dampens bow noise. All else being equal, an open tree stand maximizes game-spooking bow noise and increases your odds the target will crouch and run.

String jumping is a fact of bowhunting life, but the risk of unpleasant outcomes is greatly reduced if you understand the problem and have a plan!

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