A TEST OF THE SCENT-STATION SURVEY TECHNIQUE FOR BOBCATS

Scent-station surveys have been widely used to monitor bobcat (Felis rufus) populations, but relationships between bobcat abundance and the index derived from scent-station surveys have not been validated. In autumn 1988 and 1989 we reintroduced bobcats (n = 31) to Cumberland Island, Georgia. We conducted 15 scent-station surveys during September-February 1988, 1989, and 1990 to obtain scent-station indices (SSI) as we increased bobcat density. We found a positive relationship (r2 = 0.45, P = 0.0066) between population size and SSI. However, because SSI variance also was correlated positively with SSI, we transformed data to meet the assumption of homoscedasticity for the regression model (r2 = 0.73, P < 0.001). Predictions of population size using individual scent-station surveys bad poor precision. Analysis of statistical power indicated that 4 replicate scent-station surveys had an 80% probability of detecting only large (greater-than-or-equal-to 25%) changes in populations of high density (0.5 bobcats/km2). We recommend that (1) multiple scent-station surveys be conducted each year to monitor changes in bobcat populations; (2) SSI values should be calculated as proportions and transformed to reduce heteroscedasticity; (3) each stratum in a sampling design should contain as many stations as possible to minimize the problem of discrete data (no. of visits) analyzed as a continuous variable (proportion of stations visited); (4) scent stations should be placed as far apart as logistically feasible to minimize multiple visits by individual bobcats; and (5) results of the power analysis should be used as a minimum guideline for estimating sample-size requirements.