Understanding a whitetail’s travel and bedding habits on a particular type of terrain often takes multiple seasons and a grueling amount of scouting time. The puzzle becomes particularly challenging in broken terrain where ravines, hills, and river valleys cut through the landscape creating a whirlwind of unwanted scent dispersal. To understand why deer prefer to use particular routes, we must first break down how air currents dictate their movements. Hunting thermals and wind currents is tricky, but understanding how they carry scent is significant when deciding where and how to hunt.
Wind direction is probably the most analyzed factor when deciding where to hunt on a given day. Eddies, curls, and crosswinds can make hunting incredibly difficult and nearly impossible in some scenarios due to how the wind reacts when it meets certain terrain features. An often overlooked aspect of wind direction and currents are known as thermals. Unlike the wind which is felt in breezes and gusts, thermals are air currents that are detected as temperature shifts.
Thermals occur in uneven terrain where air rises and falls as the temperature fluctuates throughout the day. If you are going to hunt hilly terrain, it’s advantageous to have a basic understanding of how thermals work. When air cools at sunset, it falls and settles in the lowest terrain available being valleys, cuts, and draws. Conversely, as the sun heats the air in the morning, the air draft rises and pushes back to the ridgetop above. If you want to hunt at sunrise or sunset, thermals should play a role in how you hang your stands. The basic understanding of hunting thermals is to hunt high in the morning and hunt low in the evening. What that means is if you want to hunt a particular trail at sunrise, place your stand uphill/above it. As the thermal draft sweeps uphill in the morning, it will carry your scent with it. Better yet, hunt high on the ridgetop. In the evening, hunt on the downhill side of the trail so that thermal drafts will dump your scent into the valley or river drainage below. To air on the side of caution, if you can avoid hunting lower terrain, do it. The lower you drop into a valley or drainage, the more unpredictable currents will become. By hunting higher on ridges, air currents will remain more predictable.
Deer also use thermals when they are on the move. Whitetails are very in tune with wind currents so often travel, and bedding areas will directly correlate with thermals and the prevailing wind direction. For maximum scent detection, mature whitetails will put themselves in position to best detect danger from all directions. Say you are hunting a valley that runs east/west with a N/NW wind at sunrise. The most likely bedding location will be on the north side of the valley about 3/4 of the way up from the valley basin. The prevailing wind will be curling over the ridgetop, and the thermals will be drafting upwards from the valley below creating an area where danger can be detected from multiple directions.
Figuring out how and why wind currents react the way they do to a particular landscape can take a lot of time, but once you get a basic understanding of thermals, wind, and what happens when they meet with each other, you will be a more efficient hunter. There are a number of conditions that determine how wind currents move and it can be a bit confusing to break every element down. For example, if you are hunting a valley that runs north/south, the sun will hit the western basin first causing thermal activity to increase there before the sun gets high enough to warm the eastern side. Another interesting scenario is a basin with flowing water. Often, these drainage locations remain cool and air will consistently flow downward through the basin from sunrise to sunset. In this scenario, you can sneak in from the bottom undetected throughout the entire day.
How thermal currents and the wind react to terrain features is a lot like water flowing in a river. As moving water hits a rock, it splits or cuts up and curls back. The reaction is very similar to how thermals react making them very unpredictable. Wind directions will shift and swing, but thermals generally tend to do the same thing unless a weather front is moving through. The tough part is determining how the thermal current will react when it hits broken terrain.
Even the most seasoned whitetail hunter will not be able to predict wind currents 100% of the time, and each valley will likely differ from the next. Keep a close eye on thermals this season to get a better understanding of the impact that they have on whitetail behavior and movement. Some of the most important keys to getting close to mature whitetail deer are keys that we cannot see.