Good Years Can Be Bad For Deer Managers
by Dr. Grant Woods and Bryan Kinkel

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There are many factors that influence white-tailed deer growth. Hunters and managers are well aware that food quality and quantity strongly influence many aspects of herd health. Each year, clubs, landowners and managers spend consider time and monetary resources creating and maintain deer food sources, such as food plots or native vegetation management techniques that produce more browse. Often, these efforts are geared towards providing the nutritional resources deer need to express more of their potential. However, Mother Nature holds a major and unfortunately uncontrollable role in the success of these projects.

Thankfully, during 2001, Mother Nature smiled on hunters/managers in many areas of the whitetail's range. Growing conditions during the summer months of 2001 were excellent in many locations. The Southeastern US finally received the substantial summer rains needed to break the long drought that have been plaguing the region.

These improved summer growing conditions are reflected in the many property, County, and even State records that were broken during the 2001 hunting season. However, this is not to say that deer managers everywhere had reason to celebrate at the end of the 2001-02 season. For example, most of New York suffered through a summer climate that produced the third lowest amount of growing season precipitation on record.

The benefits of a receiving adequate precipitation for forage production are relatively obvious. Good forage production often equates to healthier and bigger deer. In arid regions, such as parts of Texas, it has been noted that summer rainfall and "trophy" bucks go hand in hand. The wetter the summer growing season, the more trophy-class bucks are harvested the following hunting season. Adequate summer rains will often have similar effects in more temperate climates, producing higher average body weights and antler growth per age-class. However, substantial summer rainfall does have downsides.

In sandy soils, heavy rain leaches nutrients from the soil. From a habitat management perspective, plants are simply nutrient transfer agents - they draw nutrients from the soil and transform those nutrients into a form that is edible and digestible to deer. If the soil is heavily leached, the plants have less nutrients available for transfer. The rains may increase plant growth, but because of the leaching effect, decrease plant nutrient content.

The wet conditions that produce more "trophy" bucks will also increase the health of most deer. This can be detrimental to management programs practicing "culling" - the removal of bucks not expressing a desired level of genetic potential. A good growing season can cause bucks to express more of their antler growth potential than they normally would. For a buck with poor potential, the good growing conditions can produce enough antler growth to disqualify the buck from "cull" status, even though - under the guidelines of the program - he should be culled.

Good summer growing conditions can also make protecting young bucks more difficult. With more food sources, even young bucks will put on more body and antler growth, making them look older than they really are. This can lead to the accidental harvest of bucks younger than desired. With good summer food sources, a substantial percentage of yearling bucks may be healthy enough to produce antlers that qualify them for "shooter" status, based on criteria developed during less favorable growing conditions.

Not only can good growing conditions hurt a management program by increasing the harvest of young bucks, the extra food resources can produce results that mimic a "successful" management program. After a good growing season, body weights and antler development per age class will be higher, suggesting the management program is working and producing the desired results. The extra browse produced by the better conditions can draw deer activity away from food plots, causing lower deer observation rates and less browse pressure on the plots. Data like this can give the false impression that antlerless harvests have finally controlled the population and brought the deer density in line with forage production. But these "improvements" are only temporary, and not necessarily a result of good herd and habitat management.

Just as good growing seasons can produce "inflated" management data, poor growing seasons can make situations look worse than they really are. Drought conditions, such as those experienced in New York State last summer, can greatly reduce browse growth, negatively effecting body weights and antler development. In addition, this drought-induced reduction in plant growth exaggerates over-browsing of existing plants. With less plant growth, deer may consume more plant material than is being produced.

Drought years are also very hard on food plots. Dry conditions can cause severe seed germination problems, as well as serious reductions in forage production (tonnage). During years with poor food plot germination and growth, and poor browse in the native habitat, deer can eat plots to the ground well before those food sources are most needed in late winter. Hunters/managers may actually think their food plots were a complete failure, even when the real culprits were dry conditions and hungry deer.

Reduced forage growth in both food plots and the native habitat certainly produce negative impacts on herd health indicators. Body weights and antler development per age class can decline, fawn survival and observed recruitment may decline, deer observations in open areas may increase, and food plots may be completely consumed early in the season. All these are indicators of a herd in trouble. However, they may actually be only a temporary situation caused by variable rainfall patterns.

As deer managers the important point to remember is that habitat is dynamic - in a constant state of change. Plant communities are growing in and out of various successional stages, and fluctuations in climate are producing annual variations in forage production. Hot summers, wet summers, snowy or record cold winters and even early frosts can all influence herd health and hence collected data. Because of the dynamic nature of climate and habitat conditions, these annual fluctuations in deer herd health should be considered normal. Do not fall into the trap of "living and dieing" by last year's data alone. One year"s data does not make for a trend. It is much more accurate to view data over a period of years, and then primarily as general trends - are the numbers generally getting better or worse over time?

Managers may even be able to recognize predictable patterns in herd health changes. Perhaps comparing data only from years with poor growing conditions can provide useful insight.