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Interpreting Carnivore Scent-station Surveys


Estimates of animal abundance are among the most important information needs of wildlife managers and researchers. Subjective estimates as simple as "common" or "scarce" sometimes suffice, but more objective measures are often needed. Unfortunately, secretive habits of most carnivore species and the low density of most carnivore populations preclude accurate, precise, and inexpensive estimation of population size. Hence, indices of relative abundance often substitute (see species accounts in Novak et al. 1987).

Tracks detected at scented baits (scent stations) have been used for decades to index abundances and monitor distributions of carnivores (Cook 1949, Richards and Hine 1953, Wood 1959). To facilitate comparisons among such surveys, Linhart and Knowlton (1975) introduced a standardized protocol for collecting scent-station survey data. Modifications thereof quickly found widespread application by carnivore managers and researchers (Johnson and Pelton 1981), who regarded it as an accurate and cost-effective means of monitoring trends in carnivore populations. However, despite the persistent belief that scent-station surveys provide useful information about carnivore population trends (Wood 1959, Linhart and Knowlton 1975, Roughton and Sweeny 1982, Linscombe et al. 1983, Leberg and Kennedy 1987, Travaini et al. 1996, and others), attempts to validate the method (Conner et al. 1983, Minser 1984, LeBerg and Kennedy 1987, Nottingham et al. 1989, Diefenbach et al. 1994, Smith et al. 1994, and others) have produced equivocal or conflicting results.

MN map showing biogeographic sections
Fig. 1. Map of Minnesota showing biogeographic sections (sections) and locations of scent-station survey lines, 1986-93. Boundaries of sections follow Bailey (1978), but section names are abridged.

The Minnesota carnivore scent-station survey (B. Joselyn and S. Spoolman. 1981. Predator and furbearer scent post survey. Pages 295-315 in Project descriptions, unpublished. Minnesota Department of Natural Resources, St. Paul, Minnesota, USA.) is among the most intensive long-term applications of the scent-station method. We analyzed a subset of data from that survey to determine statistical properties and to examine analyses of scent-station data. To determine sources of disagreement among validation studies and to evaluate the usefulness of survey results, we also reevaluated recent validation studies of Smith et al. (1994) and Diefenbach et al. (1994). Objectives of this paper are (1) identify key features of scent-station data; (2) discuss implications of those features for the design, analysis, and interpretation of scent-station surveys; (3) discuss a simple method of analyzing trends in scent-station indices; and (4) reevaluate the relation between scent-station visitation rates and carnivore abundance.

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