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AUTHORS: Kirby D. Bristow, Mathew J. Clement, Michelle L. Crabb, Larisa E. Harding*, Esther S. Rubin – Wildlife Research Branch, Arizona Game and Fish Department, Phoenix, AZ, USA
ABSTRACT: Elk (Cervus canadensis) populations in Arizona have historically been managed using estimates of relative abundance. Recent questions related to the influence of large wildfires, impacts to habitat, and predator-prey relations have increased the demand for absolute estimates of elk abundance. Between 2014 and 2016, we conducted experimental helicopter surveys of selected areas to compare several methods designed to model elk detection and estimate abundance. We conducted annual autumn helicopter surveys in 3 areas that contained radio-collared elk and recorded information on covariates affecting both detection (i.e., vegetative cover, vegetation type, burn category, group size, activity, and ambient light) and observer bias (i.e., observer position, pilot experience). We used information theory to rank a set of candidate a priori models to determine which covariates affected detection and select the most parsimonious models among sightability, double observer, and hybrid modeling methods. We then used the top model from each method to calculate annual site-specific elk abundance estimates for comparison to concurrent mark-recapture abundance estimates. The best supported models included all detection covariates, with the influence of covariates on elk detection generally adhering to expectations. Relative to mark-recapture estimates, the best performing hybrid model generally provided abundance estimates that were more accurate than double observer models and more precise than sightability models. The most economical methods to implement were the simultaneous double count and double observer methods, because these methods did not require model development or presence of marked animals. When applied to autumn helicopter survey data, our hybrid model should improve both precision and accuracy of elk abundance estimates.
