Plugging the Lowest Hole in the Bucket
(En anglais seulement)
By: Grant R. Woods and Bryan Kinkel
We spend considerable time and resources finding and trying to plug the lowest holes in several different buckets. No, we are not tending a whiskey still. We manage deer herds and the holes we are plugging are not to keep corn from spilling out of a feed bucket. “Plugging holes” is a scientific principle that a European scientist published several years ago. Of course he phrased it much fancier, but originally being hillbillies from Missouri and Tennessee, we felt the “hole in the bucket” illustration made more sense. The European scientist’s name was Liebig, and his principle is now known as Liebig’s Law of the Minimum.
The principle behind Liebig’s Law of the Minimum is quite simple. It means the rarest necessity an organism requires will be the limiting factor to its performance. With our “hole in the bucket” illustration, let’s say there are three holes in a bucket. One hole is near the bottom of the bucket, another about midway, and the final hole just below the top. The lowest hole limits the amount of water the bucket can hold. Plugging the upper holes will not help, since water will still pour out the lower hole. Car maintenance is another possible example. The car is the bucket, and the problems the car has are the holes. These problems (holes) limit the driving performance of the car. The car has four flat tires, a worn fan belt, and windshield wipers that don’t work.
The trick is for us to find which of these problems is the "lowest hole." The worn wipers are only an issue when it’s raining. The car will run with the worn fan belt, but if the engine is stressed the fan belt might break, severely limiting performance. On the other hand, it would be difficult to drive the car with four flat tires, at any speed or in any conditions. In this example, two of the problems only conditionally limit the car’s performance. One problem limits when the car can be driven, while the other problem limits how hard it can be driven. But the last problem, the four flat tires, limits the vehicle’s performance all the time under all conditions. The four flat tires are the “lowest hole in the bucket.” and are the greatest restriction to performance.
If only finding the “lowest hole” in the deer herd performance bucket was that easy. As wildlife managers, we spend much of our time finding and plugging the lowest hole in herd performance. It is important to realize that if all the mid and upper level holes can be plugged in the deer management bucket, the herd’s quality will still drain to the level of the lowest hole. Therefore it is important for deer managers to realize that the lowest hole is the most important to plug. Herd quality cannot rise above the lowest hole on a sustained basis.
Continuing our bucket illustration, sometimes water can be poured into the bucket so fast that the water level temporarily rises above the lowest hole; only to fall back once the water flow is slowed. Similarly, sometimes managers get fooled when something pours into the herd bucket rapidly enough that herd quality temporarily rises above the management low hole. For example, there was a large acorn crop throughout most of the whitetail’s range during the fall of 1999. Average body weights were relatively high, food plot utilization decreased, and deer observations per unit effort were relatively low as herds were dispersed throughout hardwood areas.
These indicators were good, and many managers were quick to state that their “management” programs had succeeded. They finally had a handle on their deer herd! But deer herds and their habitat are dynamic—in a state of constant change. In fact, the fall of 2000 was a completely different story. The total acorn crop was significantly lower in many areas. Many food plots we observed from Texas to New York were heavily utilized by November, and were down to “lip high” (eaten to the ground) by January. By the time green-up occurs in 2001, many herds will be nutritionally stressed by low winter food resources, and will exhibit below average body weights. This will result in decreased herd performance, considering does will be preparing to fawn, and bucks will be preparing to grow enough bone material (antlers) to equal the volume of a human arm.
Low spring body weights are not uncommon. Throughout the whitetail’s range, the most common low hole in the deer management bucket is a lack of quality nutrition. In fact, malnourishment is considered the most common disease among whitetail herds. We believe deer managers frequently overlook the nutritional “low hole” for three primary reasons:
- Quality food resources are most likely to be limited during late summer and late winter, when deer managers are least likely to be monitoring deer and habitat condition.
- It can be difficult for many managers to distinguish the difference between high and low quality deer forage.
- Malnutrition is often misdiagnosed because it results in diseases and other mortality factors that receive the blame.
If quality nutrition is the limiting factor for a herd, plugging the higher holes will not yield positive results. For example, there are a growing number of deer managers who are trying to plug the genetics “hole.” They believe that importing “better genetics” into their herd is the key to improving quality. In many of these cases, nutritional resources are actually the limiting factor in herd quality and not “poor” genetic potential. If a genetics hole exists at all, it is usually very high on the bucket. Plugging this upper hole would still allow herd quality to pour rapidly out the nutrition hole at the bottom of the bucket.
In addition, if the substantial resources spent “improving” the genetics had been directed toward the nutritional problem, the lowest hole would have been plugged and the quality level within the herd bucket would have risen significantly.
We have also seen cases where the lowest hole is not related to the habitat or the deer herd, but to the hunters. A large portion of successful management is not just “deer” management, but “people” management—more specifically, “hunter” management. Sometimes, hunters aren’t willing to expend the necessary time and energy to harvest an appropriate number of antlerless deer. Most folks involved with a successful QDM program will admit this can be a tedious job.
Another low hole in the “hunter” management bucket we have dealt with is hunting techniques. Even if the deer management holes have been plugged, with herd quality and buck age-structure goals met, if hunters are not harvesting those older bucks, the harvest and hunter satisfaction aspects of the program are not complete. Some hunters simply don’t realize hunting techniques that were very successful on yearling bucks may not be effective on older-age bucks. When it comes to activity patterns, mature bucks can almost be considered an entirely different species than yearling bucks. Successfully harvesting older-age bucks usually requires unique strategies. Plugging the lowest hole in the bucket may actually entail teaching better hunting techniques.
Whether on the biological or human side of the bucket, finding the lowest hole on a given property usually requires site-specific data. Unless the lowest hole is determined and plugged, efforts toward fixing the higher holes would be like trying to improve a car’s performance by changing the wipers when it has four flat tires.
Dr. Grant Woods and Bryan Kinkel are research biologists with Woods and Associates, Inc. Both are involved in research concerning deer population dynamics, deer behavior, and advancements in forage production. Grant and Bryan also assist hunting clubs and private landowners throughout the U.S. to improve the quality of their deer herds through site–specific management techniques. Members of Woods and Associates are regular contributors to Quality Whitetails.