Scent Station Surveys in Minnesota with Reference to
Predator Management
WILLIAM E. BERG
Minnesota Department of Natural Resources, 1201 East Highway 2,
Grand Rapids, MN 55744
The U.S. Fish and Wildlife Service (USFWS) initiated the "Indices of Predator Abundance in the Western United States" survey in 1972, with the objective of obtaining annual changes in visitation indices for various predators attracted to standardized scent station lines. Minnesota Department of Natural Resources (MNDNR) joined the survey on an experimental basis in 1975. Although the USFWS discontinued sponsorship of this survey in all states in 1981, and most states opted not to continue on their own, Minnesota has continued and greatly expanded the scent station survey.
Minnesota's scent station survey is interagency in scope, and involves the cooperation of MNDNR, all USFWS National Wildlife Refuges and Wetlands Districts, both National Forests, and various Indian reservations, county land departments, and colleges. The objectives of the survey are to determine the distribution of and annual visitation indices for red fox, striped skunk, raccoon, coyote, dog, cat, wolf, bobcat, and black bear. Inferences of the relationship between visitation indices and population trends have been established in several studies for coyotes, red fox, raccoon, gray fox, bobcats, and bear. Presently, Minnesota's survey consists of 92 routes containing a total of 407 4.3-km segments and 4,070 scent stations. Scent stations are spaced 0.43 km apart and utilize plaster-of-Paris fatty acid scent (FAS) discs purchased from the U.S. Department of Agriculture's Pocatello Supply Depot. Each scent station is checked for one night only during September. Approximate sampling intensities in the Forest, Transition, and Farm Survey Zones are one scent station per 44 km², one per 55 km², and one per 69 km², respectively. Statistical analyses utilize the Wilcoxon signed rank and Fisher randomization tests, both of which are suitable for testing non-parametric paired independent samples.
The multi-species aspects of Minnesota's scent station surveys present several applications for the data. Scent stations have documented generally increasing visitation indices for red fox and skunk and stable indices for raccoon statewide since 1976. The Minnesota Department of Health uses the skunk index to predict rabies outbreaks. Scent stations have also documented the immigration (and population establishment) of coyotes from Minnesota's northern forests to the Transition and Farm Survey Zones. Wolf visitation data imply an increasing wolf population and range; this was documented in a comprehensive wolf survey in winter 1988-89. Data from bobcat visitations and distribution provide inputs into Minnesota's annual bobcat population model. Data from intensive scent station surveys by the USFWS Wetlands Management Districts in west-central Minnesota aid in the evaluation of predator removal efforts. Scent stations also provide a learning opportunity for field stations of educational institutions.
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