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simulated-nest index may have been affected by
factors independent of population size. Variation in
prey availability may have influenced predator
response to bait and therefore their trapability as
well as their destruction of simulated nests. We can-
not distinguish between these possibilities with our
data, but Smith and Brisbin (1984) concluded that
capture probability of raccoon, opossum and gray
fox differed greatly among years and that total cap-
tures did not reflect population changes.
Management Implications
As applied in this study, spotlight counts, scent-
station surveys and simulated-nest surveys were
imprecise, i.e., there was large within year and
within area variation. Spotlight counts of skunks and
opossums had coefficients of variation similar to
those of scent-station indices. Coefficients of varia-
tion for the simulated-nest index and raccoon spot-
light counts were approximately 50% smaller than
scent-station indices, but were still relatively large.
Because of the variability of the 3 survey tech-
niques, extremely large sample sizes are required
to reliably detect changes in population indices on
the order of 20-50%. However, we did observe sig-
nificant differences between years in the three
indices with sample sizes of 15-30 (areas pooled),
when changes in population indices were on the
order of 2-5 fold. Fluctuations of this magnitude
have been frequently reported for populations of
striped skunks (Allen and Shapton 1942, Bjorge
et al. 1981, Fuller and Kuehn 1985, Verts 1967).
Seidensticker et al. (1987) described a doubling in
opossum density in 1 year followed by a decline of
equal magnitude. Population eruptions have been
inferred from Hudson's Bay Company records of
raccoon fur sales (Sanderson 1951), but Fritzell
(1982) attributed the eruptions in fur sales to
changes in the market process. He presented rac-
coon fur sales records from other companies that
exhibited 2 fold changes over 2-3 years and sug-
gested that these reflected normal fluctuations.
Despite their imprecision, scent-station surveys,
spotlight counts and simulated-nest surveys appear
to be capable of detecting large population changes
with a moderate level of effort.
Many managers consider scent-station surveys
useful due to their uniformity, repeatability and cost-
effectiveness (Brady 1979). An additional advantage
is the ability to obtain data for a number of species
with a single survey (Linscombe et al. 1983). Spotlight
surveys for furbearers would be more cost-effective if
they could be incorporated into surveys conducted for
other species such as deer (Rybarczyk et at. 1981).
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