Refining the Equation for Interpreting Prey Occurrence in Gray Wolf Scats

The degree to which relative frequencies of large ungulates in wolf scats represent the proportion of prey consumed is unknown. Thus, I fed mule deer (Odocoileus hemionus), elk (Cervus elaphus), and moose (Alces alces) carcasses to 3 captive gray wolves (Canis lupis; hereafter referred to as wolves) to refine interpretation of prey occurrence in wolf scats. The mass (kg) of prey per collectable scat (Y) increased as the body mass of prey (X) increased (r2=0.96). The slope of the linear regression (b = 0.008) differed (P < 0.001) from that of Floyd et al. (1978) (b = 0.020), but not from that of Traves (1983) (b = 0.011) (P = 0.13). I recommend using an equation (Y = 0.439 + 0.008X) derived from combined studies that spans prey sizes from snowshoe hare (Lepus americanus) to adult moose and is robust to variable field conditions. Maximum bias of up to 50% using frequency of occurrence (percentage of scats) occurs when 1 very small (e.g., beaver [Castor canadensis]) and 1 very large (e.g., adult moose) prey make up 20-80% of the scats. Previous studies that have extrapolated from the Floyd et al. (1978) equation for interpreting occurrence of adult elk and moose in wolf scats may have overestimated relative numbers and biomass of these large cervids by up to 18%.