. Brigham Young University science bulletin. Biology -- Periodicals. :Ai. Series. \'() 18, No. 3 BuEEDiNt; Ecology of Uiaii HAProns 67 area (although not ' representing the smallest prey which might be taken). Relationship betiveen Raptors and Their Preij. In examining the food habits of raptors, the frequency percentage of prev items can be considered to reflect the prey species which the raptors are expending time and energy to ob- tain, whereas the biomass percentages essentially reveal what prey species sustain the raptors. Logically, raptors will be most efficient
. Brigham Young University science bulletin. Biology -- Periodicals. :Ai. Series. \'() 18, No. 3 BuEEDiNt; Ecology of Uiaii HAProns 67 area (although not ' representing the smallest prey which might be taken). Relationship betiveen Raptors and Their Preij. In examining the food habits of raptors, the frequency percentage of prev items can be considered to reflect the prey species which the raptors are expending time and energy to ob- tain, whereas the biomass percentages essentially reveal what prey species sustain the raptors. Logically, raptors will be most efficient if they can expend their energies on the largest prey species which they are able to safely capture and kill, thereby achieving a maximization of the ratio between the food biomass necessarv for their daily energy budget and their energy- expending hunting time. An analysis of the raptor-prey size relationships on the study area reveals this to be the case (Fig. 26), and a gradual increase in mean prey weight was found to correspond with an increase in average raptor species weight. The regression of the two vari- ables results in a positive slope of ± , significantly larger than zero at the level (t ^ ). There were no significant vari- ations in mean prey weight between raptors of approximately the same weight. This is evident in comparisons of mean prey weights of the Ruteo hawks and Great Horned Owl and points up the fact that these species must bv directly com- peting for the same food. In summary, the predatoiy habits of these raptors reflect pre\ a\aiiabilitv and a size dif- i 1000. Fig. 26. Relationship between raptor weiglit and mean weight of prey .species taken. N'umhers refer to raptor species and follow standard te.\t numbers. The number refers to the Long-eared Owl, in- cluded in this correlation analysis. ferential selection correlating with the raptor's body weight. Although apparently no available prey species was too small to serve pot
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