Northern Prairie Wildlife Research Center
Glen A. Sargeant
Northern Prairie Science Center
William E. Berg
Minnesota Department of Natural Resources
Douglas H. Johnson
Northern Prairie Science Center
Biologists frequently require information about carnivore abundance. Unfortunately, most species of carnivores are shy, secretive, and notoriously difficult to count. Scent-station surveys are an alternative method of tracking changes in carnivore numbers. Rather than counting animals, observers record visits by carnivores to scented baits. The proportion of baits visited is assumed to reflect carnivore abundance.
The Minnesota Department of Natural Resources (MDNR) began using scent-station surveys to monitor carnivores in 1976. The United States Fish and Wildlife Service (USFWS) joined forces with the DNR effort in 1986. Since 1986, the two agencies have overseen the operation of more than 3,000 scent stations each year. Results of this cooperative effort are presented in this portion of the NPWRC home page.
A scent station consists of a 0.9-m diameter circle of smoothed earth with a fatty-acid scent tablet placed at the center. Scent stations are placed along unpaved roads at intervals of 480 m; 10 stations constitute a line. Minimum spacing between lines is 5 km. Locations of lines are shown on the map in the section "View Locations of Survey Lines" listed below. Stations within lines are operated simultaneously for 1 night each year between late August and mid-October, though not all lines can be operated every year. Presence or absence of tracks is recorded for individual species when stations are checked the day after activation. The index presented here is the proportion of lines with one or more visited stations. Curves were fit to index values by LOWESS smoothing.
Scent station data cannot be converted to estimates of abundance. For example, it is impossible to use the index to determine the number of coyotes in Minnesota. Fortunately, it is seldom necessary to know exactly how many individuals are present to manage a carnivore population. Often, it is enough to know whether a species is maintaining its geographic distribution and increasing or decreasing in abundance over time. Trends in scent station data seem to parallel changes in carnivore abundance and can be used to assess long-term trends in carnivore populations.
You can access trends in carnivore indices from 1986 to present from this location on the Northern Prairie Wildlife Research Center Home Page. Simply choose a geographic area or species of interest from the lists below to obtain results for wolves, coyotes, red foxes, skunks, and raccoons. To compare results for different parts of Minnesota, choose Spatial Patterns.
Note: Scent station surveys depict general trends only. Comparisons more specific than those shown here may not give reliable results.
Note: Sometimes scent station surveys fail to detect species when they are indeed present. In particular, wolves and bobcats may be present in some areas where they have not been detected by this method.
This resource should be cited as:
Sargeant, Glen A., William E. Berg, and Douglas H. Johnson. 1996. Minnesota carnivore population index scent-station survey results, 1986-95. Jamestown, ND: Northern Prairie Wildlife Research Center Online. http://www.npwrc.usgs.gov/resource/mammals/mncarns/index.htm (Version 16JUL97).