String Jumpers: How to Aim at Alert Deer

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How do you aim when bowhunting jittery whitetails?

Deer have the amazing ability to react to the sound of the shot. They start to move before the arrow ever arrives at its destination. We call this “string jumping.”

Generally, the deer hears the limbs bottom and then immediately drops to load its legs in an effort to bolt. In the process of dropping, the deer seems to duck under the string as if on purpose. This is just the way it appears. Actually, it is an involuntary reaction to a startling noise.

If you haven’t watched a hunting video and seen the slow-motion replay of a buck dropping 6 inches in the time it takes the arrow to reach him, you may still think that many of your misses were simply poor shots. You will be surprised to realize that some of your high misses were actually perfect shots – at the spot where the deer used to be standing.

Aim correctly on deer likely to "jump the string." (Bill Konway photo)

Reaction Time

Sound travels at approximately 1,085 feet per second. It takes .056 seconds for the sound of the limbs bottoming to reach a deer that’s 20 yards from the base of your tree. If you shoot an arrow that travels 230 fps, it will take .275 seconds for the arrow to arrive. That gives the deer roughly .22 seconds to start dropping. 

From watching plenty of deer hunting videos, it would appear that a deer’s reaction time to a startling sound is nearly instantaneous. We must attempt to gauge this amazing phenomenon so we can determine how low to aim when shooting at a likely string jumper.

Let’s assume that a deer’s reaction time is about half that of the very best human. When it comes to reflexes, the most highly trained humans are track athletes anticipating the starting gun. Studies have proven to the satisfaction of the track and field community that anything less than a tenth of a second reaction time (measured electronically in the starting blocks) is anticipation, and therefore they consider this a false start. If .1 seconds is the quickest reaction time of the world’s best athletes poised for the starting gun, then .05 seconds is probably a reasonable average for whitetail deer. I have had a few people suggest that this is too fast; maybe so. But if it is, then the deer don’t drop quite as far as my studies suggest, but the conclusions are still valid.

When you take .05 seconds from .22 seconds (the difference between the time it takes the sound to arrive and the arrow to arrive on a 20-yard shot with a 230 fps arrow) that leaves a lot of time for gravity to work. The time difference is less with a faster arrow.

At 20 yards, you have to aim about 6 inches low on an obvious string jumper with a 230 fps arrow. In most cases, this is below the brisket. With the 280 fps arrow, you need to aim about 3 inches low. At 30 yards, the advantage is even more pronounced. You have to aim fully 17 inches low to hit the vitals of a string jumper with the slower arrow. With the faster arrow, you still need to aim 10 inches low – well below the brisket.

Recognizing a String Jumper

None of this means diddlysquat if you aren’t able to tell which deer are likely to jump the string. In some cases, you have to assume they will jump even if they are relaxed. It gets tough, and in the end, experience is important. This is especially true among southern deer. They are much more likely to drop at the sound of the shot than northern deer, even when they are feeding in a relaxed manner.

In general, does tend to jump the string more often than bucks. According to Jim Perkins, a southern guide with more than a thousand guided kills under his belt, about 95% of southern does make at least some attempt to jump the string and only about 50% of the bucks. Among northern deer, the numbers are much lower. However even northern deer will often jump the string if they are tense and alert. 

When I’m hunting deer north of the far southern tier of states, I never aim low unless the deer is obviously tense and then I never aim below the brisket. That is how I have learned to play the odds on these deer. However, in the Deep South, I always aim as if the deer is going to jump – a little higher (bottom of the heart) for bucks, and lower (at the brisket or below) for does. If the bucks are obviously spooky, I aim below the brisket on them also.

Conclusion

If my assumptions about reaction time are even reasonably close, deer barely have time to twitch before the arrow arrives at distances inside 10 yards. For this reason, arrow speed means almost nothing at these close distances. However, at longer ranges you will gain an increasing advantage with a faster arrow. When hunting whitetails that are likely to jump the string, a fast, quiet bow is a definite advantage.

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