During deer season a couple of years ago, a good friend of mine was out in the woods with his longbow and self-made arrows. All of his stuff was self-made; the bow, the arrows, the quiver, the tree stand, and even some of his clothes. He is self-sufficient and doesn’t ask for much help. When I got a call from him asking if I had my infrared camera at the house one evening, I was surprised and asked if he had a problem at his house or one of his relatives. The last thing on my mind was what he was after. In a long and drawn out manner, he finally got to the question he wanted to ask. He wanted to know if I could help him find a deer he had shot before sundown. While there are some legal, ethical and moral questions surrounding the use of infrared to track or hunt deer, I opted to help out because the deer was already shot. Of course I said I would help. What are buddies for, if not to help track a downed deer in the dark?
Curious as to why he wanted the camera, I asked him and he replied after he’d shot the deer he wasn’t entirely sure where it went. The rest of the story unfolded. “There isn’t much of a trail to follow,” he said. “I must have hit it a little higher than I thought. The camera of yours can see the body heat of the deer right?”
On this particular night with an air temperature of about 40°F, one should be able to see a mass that is about 90°F, depending on how long the critter was down. Full of confidence, I headed in the direction of the hunting grounds and where my buddy said he was with my trusty IR camera. The system was a hand-held camera with a 320 by 240 array and a wide angle lens (I took the telephoto lens just in case). I parked the truck and turned on the system to form an idea of what to expect. I looked around and spotted some squirrels in a nearby tree. They stood out fairly well from the surroundings. I figured we had this in the bag. I set my level and span to the squirrel and proceeded to walk around and scan as far as I could see. I was looking for any telltale “hot” spots. I found my buddy’s footprints in the area where he was pacing, waiting for me to show up. I pointed this out to him and declared “this is going to be easy!”
Although I was confident, I failed in this endeavor to “Think Thermally.” Many may already know a few things about our friend, the white-tailed deer. One small detail I overlooked is the hair on a white-tailed deer is hollow, making it one of the best insulators in nature. We searched in a half-moon pattern of widening arcs for hours (four hours to be exact!). Heading back to the trucks for more flashlight batteries, we cut a straight line in that direction and about ¾ of the way back I spotted a small heat signature under a bush. I was going to dismiss it as being a rabbit (we located several of them this evening), but this one didn’t move as we got closer and closer until it was apparent that we had indeed located our furry friend, the downed deer.
All I was detecting was the sparsely covered belly and small areas around the nose and eyes. The rest of the deer “appeared” to be at or very near to air temperature. We had passed within ten feet of the other side of the same bush and had no any indication of a heat source under that bush. Then as if struck with a sledgehammer, it hit me! The insulating quality of the deer’s coat prevented, or drastically reduced the transfer of heat from the body of the deer to the outer surface of the coat. I knew the coat insulated well, but never before applied any kind of technology into locating one by heat output.
Looking at the rabbits and squirrels did not help me define the level and span I would need to locate a deer (my first mistake and the second mistake was being overconfident). Their coats do not perform nearly as well as the deer’s coat at preventing or reducing heat loss.
Therefore, by all means think outside the box. Remember to “Think Thermally.” You never know what you will find.