Northern Prairie Wildlife Research Center
What exactly does distribution mean? It is the number of animals in an area, or the area over which the animal occurs? For example, if someone sees a coyote in the Fargo area, does that mean there are a lot of coyotes in the Fargo area?
A term like distribution can be confusing. In biology, we relate distribution to species that inhabit a certain area regardless of their population density. While distribution and density are related, they can be significantly different in their meanings.
Again, let's use the coyote observation in the Fargo area as an example. The coyote density near Fargo could be practically nonexistent even though one was observed. However, the density had to be more than zero or a coyote would not have been observed there in the first place.
We can gain some insight into the distribution and roughly how many coyotes may be in the Fargo area by comparing how often we see coyotes relative to some other closely related species - such as red fox. We can fine-tune this even more by comparing the relative occurrence of the two species in the four main physiographic regions of North Dakota.
Physiographic regions are generally large areas, and differ from each other in land form and topography. Land form generally takes into account things like past geological changes between areas (e.g. glacial Lake Agassiz - Red River Valley) and how the land looks today. For example, the Missouri Coteau pothole country looks different from the badlands, and they both look vastly different than the Red River Valley, even though all these are called prairie or grassland.
This introduction is necessary so that you aren't confused into thinking that distribution equals densities or numbers of animals, or assume there are no real differences between physiographic regions, because they are all called prairie.
With that understanding, let's take a look at the relative distribution of red fox and coyotes in North Dakota; what changes have occurred over time in different regions; and some reasons for the change.
Because the information we need isn't all in one spot, we have to look in several places to find what we need. One source is data on fur harvests both questionnaires and fur buyer reports. Analysis of these data to answer our questions is complicated by annual changes in fur pelt prices. Variable pelt prices affect harvest size. In addition, these data are only available as state wide totals and are not easily separated out by physiographic region. Similar problems exist with historical bounty information.
Fortunately, we have good information available from the winter whitetail deer survey in North Dakota since 1960 - not as many years as we would like, but some of the best quality data available.
This is good survey for whitetail deer. Each year the survey is flown, in addition to its main purpose of counting deer, observers record the number of red fox and coyotes seen on the study areas.
We divide the numbers of red fox and coyotes seen by the number of hours flown - this is called "weighting." The survey data must be weighted in some fashion because the more you look for something the more of it you will find. Weighting takes "the more you look the more you find" variable into account so that results can be compared between areas in a reasonably unbiased manner regardless of size or search effort.
While the aerial deer survey provides some of our best fox and coyote distribution and density information, some years there is not enough snow to conduct the survey in some study areas. Several years in the 1980's had insufficient snow cover, and therefore the graphs accompanying this article have some years with missing data.