Douglas H. Johnson
W. E. Berg
G.A. Sargeant
2003
<p>Scent<span> stations usually are deployed in clusters to expedite data collection and increase the number of stations that can be operated for a given cost. Presumed benefits of cluster </span>sampling<span> may not be realized, however, unless cluster sizes are chosen with respect to </span>sampling<span> variation within and among clusters. To encourage and facilitate the use of efficient </span>designs<span> and reporting standards, we used data collected in Minnesota, USA, during 1986-1991 to (1) compare the performance of </span>survey<span> </span>designs<span> with various numbers of stations/cluster; (2) estimate relations between required sample sizes and visitation rates, changes in visitation rates, and error rates; and (3) compare 2 measures of </span>carnivore<span> response: proportions of </span>scent<span> stations (</span>station<span> index) and proportions of clusters (line index) visited by red foxes (Vulpes vulpes) and striped skunks (Mephitis mephitis). Despite broad ecological differences between the species, results were similar for foxes and skunks. Foxes visited 2-21% of stations and 15-84% of lines. Skunks visited 1-16% of stations and 3-54% of lines. </span>Station<span> and line indices were closely related (r</span><sup>2</sup><span> > 0.86) and were similarly sensitive indicators of change in visitation rates. Low visitation rates greatly limited the potential usefulness of </span>scent<span>-</span>station<span> </span>surveys<span> because required minimum sample sizes increased exponentially as visitation rates decreased. For visitation rates below 5-10%, required minimum sample sizes were very large and difficult to anticipate. Relative to single-stage </span>sampling<span>, cluster </span>sampling<span> with 10 stations/cluster inflated sample variances, hence sample sizes required to achieve a fixed level of precision, by a factor of 1.6-2.2. Cluster </span>sampling<span> is advantageous only when cost savings permit increases in sample sizes that outweigh concomitant increases in </span>sampling<span> variability. Costs and </span>sampling<span> variation both should be considered when choosing </span>survey<span> </span>designs<span>, and </span>designs<span> should be evaluated and refined as data accumulate.</span></p>
application/pdf
10.2307/3802770
en
Wildlife Society
Sampling designs for carnivore scent-station surveys
article