Proceedings of the Seventh Mountain Lion Workshop

142
ESTIMATING COUGAR ABUNDANCE USING PROBABILITY SAMPLING: AN
EVALUATION OF TRANSECT VERSUS BLOCK DESIGN
CHUCK R. ANDERSON, JR., Wyoming Cooperative Fish and Wildlife Research Unit, Box
3166, University Station, Laramie, WY 82071. USA, email: cander@uwyo.edu
FRED G. LINDZEY, Wyoming Cooperative Fish and Wildlife Research Unit, Box 3166,
University Station, Laramie, WY 82071, USA, email: flindzey@uwyo.edu
NATE P. NIBBELINK. Wyoming Geographic Information Science Center, University of
Wyoming, Box 4008, University Station, Laramie, WY 82071, USA, email:
nathan@uwyo.edu
Abstract: We used GPS data records of cougar track sets (n = 5-6 locations/night) to evaluate
accuracy and precision of Transect Probability Sampling (TPS) and Block Probability Sampling
(BPS) from spatial simulations of varying cougar densities, sampling efforts, and number of
track set nights. GPS data records yielded 446 1-night track sets and 225 2-night track sets from
12 cougars (2 adult males, 6 adult females, and 4 subadults) for simulations. Accuracy and
precision of TPS and BPS estimates generally improved with increased cougar density, sampling
effort, and number of track set nights, but TPS estimates were vulnerable to extremely short
track sets (e.g., cougars at kill sites) and BPS estimates were exceedingly imprecise. To address
these problems, we adjusted TPS estimates based on the proportion of cougar track sets
estimated to be at kill sites and used bootstrap techniques to estimate 90% confidence intervals
(CIs) around BPS estimates. TPS estimates adjusted for cougars at kill sites typically improved
accuracy, precision, and estimator reliability (CIs approaching 90% coverage). Bootstrapping
greatly reduced variance around BPS estimates but exaggerated precision (i.e., CI coverage
typically below 90%), likely due to low cougar detection rates. Comparisons of adjusted TPS
and BPS estimates suggested higher cougar detection rates and improved accuracy from TPS
surveys, with more reliable CI coverage. TPS simulations suggested reliable cougar population
estimates could be obtained from high-effort surveys (~2 km transect spacing) regardless of
cougar density or number of track set nights, or from medium-effort surveys (~3 km transect
spacing) of medium-high density populations (2.3-3.5 independent cougars/100 km 2 ) sampling
2-night track sets. Ninety-percent CIs suggested population changes of 27-30% could be
detected using high effort surveys of 1-night track sets, 20-24% from medium effort surveys of
2-night track sets, and 15-18% from high effort surveys of 2-night track sets. Because of the
time and expense required to conduct high effort TPS surveys, we propose sampling cougar track
sets without intense tracking efforts and applying perpendicular track lengths we measured to
estimate cougar population parameters.
PROCEEDINGS OF THE SEVENTH MOUNTAIN LION WORKSHOP