Investigating Food Habits of Terrestrial Vertebrates
173
Development of digestibility coefficients or conversion factors seems to
have the greatest potential for estimating actual biomass consumed. Correction factors are generated by feeding known amounts of forage or prey, collecting the resulting fecal material, and weighing the contents. These results
can then be used with volumetric estimates or weights of prey remains to create a diet profile (table 5.2). Ideally, an investigator should use consumer-specific correction factors. Hewitt and Robbins (1996) also recommended developing correction factors for specific foods. Until such correction factors are
derived, however, it may be useful for investigators to apply existing correction
factors developed for general food or prey categories (e.g., foliage, fruits, nuts,
small vertebrates) as long as the feeding trails used to generate the correction
factors and their subsequent application are trophic-level specific (i.e., correction factors developed for carnivores are applied to carnivores and not to herbivores). Although there may be interspecific differences in digestion efficiencies within a trophic level (compare Litvaitis and Mautz 1980 with Powers et
Figure 5.1 Comparison of four methods used to investigate prey use by wolves. Fecal samples
obtained from free-ranging wolves in Italy. Occurrence was the percentage of each prey relative to
total occurrences of all prey. Dry weight was a percentage of all weight of all prey remains recovered
in fecal samples. Volume was estimated using a reference grid and each prey was expressed as a
percentage of the total volume of the feces. Estimated biomass was estimated using correction factors based on feeding trials conducted by Weaver (1993). Redrawn from Ciucci et al. (1996).
173
Development of digestibility coefficients or conversion factors seems to
have the greatest potential for estimating actual biomass consumed. Correction factors are generated by feeding known amounts of forage or prey, collecting the resulting fecal material, and weighing the contents. These results
can then be used with volumetric estimates or weights of prey remains to create a diet profile (table 5.2). Ideally, an investigator should use consumer-specific correction factors. Hewitt and Robbins (1996) also recommended developing correction factors for specific foods. Until such correction factors are
derived, however, it may be useful for investigators to apply existing correction
factors developed for general food or prey categories (e.g., foliage, fruits, nuts,
small vertebrates) as long as the feeding trails used to generate the correction
factors and their subsequent application are trophic-level specific (i.e., correction factors developed for carnivores are applied to carnivores and not to herbivores). Although there may be interspecific differences in digestion efficiencies within a trophic level (compare Litvaitis and Mautz 1980 with Powers et
Figure 5.1 Comparison of four methods used to investigate prey use by wolves. Fecal samples
obtained from free-ranging wolves in Italy. Occurrence was the percentage of each prey relative to
total occurrences of all prey. Dry weight was a percentage of all weight of all prey remains recovered
in fecal samples. Volume was estimated using a reference grid and each prey was expressed as a
percentage of the total volume of the feces. Estimated biomass was estimated using correction factors based on feeding trials conducted by Weaver (1993). Redrawn from Ciucci et al. (1996).