Walk into a small-town diner during any fall in Northeast Michigan and one will invariably hear hunters discussing the population status of their favorite game species.

How many whitetail deer are there? Have ruffed grouse numbers gone up or down?

While such discussions are an easy way to interact over food and drinks, determining the distribution and population size of any given species of flora and fauna is actually exceedingly difficult. And determining the magnitude or rate of change in population parameters is even more challenging, especially when the target organism is a highly mobile animal species.

In fact, an entire body of science, biostatistics, is devoted to these challenges.

An “inventory” is a structured sampling that aims to determine the distribution, composition, or one-time abundance of a given parameter of interest. For example, an inventory may be conducted to determine how many species of songbirds occupy a given forest stand in a given breeding season. Conversely, “monitoring” documents rates of change in a parameter or is used to determine the effects of a treatment. For example, one might monitor what the five-year effects of a silvicultural treatment has on a forest songbird community.

While inventory or monitoring by themselves are not science, per se, they are intricately linked to the scientific process. Science, as previously defined is, “the use of evidence to construct testable explanation and prediction of natural phenomena, as well as the knowledge generated through this process.” Science is done when hypotheses are stated, data are collected and analyzed, and papers that describe methods and results are submitted for peer review, subsequent revisions, and acceptance or rejection. Many papers are focused on improving inventory and monitoring methods.

A well-constructed and well-employed inventory and monitoring program considers precision and accuracy. Precision is the ability to repeat an activity and produce the same result. Consider an archer shooting at a bullseye on a target. Precision is the ability of the arrow to hit the same mark (not necessarily the bullseye) repeatedly. In other words, precision is a measurement of the distance between each shot arrow. Accuracy is something quite different. Accuracy is measured by how close the arrow comes to the bullseye (the actual targeted value).

But how does one construct inventories or monitoring exercises with precision and accuracy?

Here’s where science comes into play.

Many scientific papers delve into ways to conduct inventory and monitoring with greater degrees of precision and accuracy. Besides financial and time limitations that always exist, other factors also impact most inventory or monitoring attempts. For example, the sharp-tailed grouse is a game species with a current distribution in Michigan restricted to the eastern Upper Peninsula. Birds gather at specific locations during the spring where males display to females. It is during that time of the year that surveys are conducted to monitor the current distribution of birds and their population.

But sharp-tailed grouse are highly mobile, making counting them difficult. For instance, there exists the possibility of double-counting birds (producing an inflated population estimate) if birds move and are counted more than once. Or, if birds spend their time in an unsampled area, they might not be seen by surveyors and end up uncounted (producing a depressed population estimate).

A paper in the Journal of Wildlife Management showed that the surrounding landscape (whether agricultural, forest, or wetland) influenced bird movement to different degrees. In other words, precision and accuracy of bird counts differed because of broad environmental factors and a correction factor for landscape types was developed.

Another problem that may exist is that different people conducting surveys are seeing different things or doing work differently. Those are called “biases”. A follow-up sharp-tailed grouse study in the Journal of Fish and Wildlife Management showed that citizen scientists trained via in-person sessions or via recorded teaching videos conducted surveys differently. The type of training, therefore, can influence precision and accuracy, as well.

Evidence-based natural resource management rests, to a considerable degree, on the review of scientific literature to provide a conceptual basis to work. When the scientific literature is scant, inventory and monitoring may be even more important. For example, many invasive plants are treated with herbicides, but specific literature regarding the efficacy of treatments may not exist for all localities. For those types of projects, in particular, monitoring is important to document effects and guide future actions.

For more information and see how a government agency addresses this topic, see the National Park Service’s website: nps.gov/im/index.htm

Greg Corace is the forester for the Alpena-Montmorency Conservation District. For more information, including sources used in this article, Greg can be contacted at greg.corace@macd.org or 989-356-3596, ext. 102.