Sightability Adjustment Methods for Aerial Surveys of Wildlife Populations

Mountain goat abundance and population trends in the Olympic Mountains, northwestern Washington, 2016

“…We estimated mountain goat abundance using the sightability modeling approach developed by Samuel and others (1987) and Steinhorst and Samuel (1989). This approach combines counts of animals, or groups of animals, in a set of randomly sampled survey units with a model for their probability of detection.…”

“…The estimated regression coefficients (β � ; Rice and others, 2009, p. 474) and their estimated unconditional variance/covariance matrix, Σ � (Rice and others, 2009, p. 474), were then used to estimate the sightability correction factors using the following equation from Steinhorst and Samuel (1989):…”

“…Wong (1996) developed consistent (asymptotically unbiased) estimators of each of these variance components. We estimated ̂ based on the Steinhorst and Samuel (1989) estimator (eq. 1), and Var() using equations from Wong (1996) as applied in R SightabilityModel package (R Development Core Team, 2011;Fieberg, 2012).…”

Mountain goat abundance and population trends in the Olympic Mountains, Washington, 2011

“…We estimated mountain goat abundance using the sightability modeling approach developed by Steinhorst and Samuel (1989). This approach combines counts of animals, or groups of animals, in a set of randomly sampled survey units with a model for their probability of detection.…”

“…We estimated sightability correction factors for each observed group using model-averaged regression coefficients and their unconditional variance covariance matrix from Rice and others (2009) along with formulas from Steinhorst and Samuel (1989). Specifically, Rice and others (2009) used sighting data from 205 sightability trials to model the probability of detection for each mountain goat group (j),…”