LAUSR

Abstract: Appropriate diets for ex situ wildlife are essential for animal health and welfare and yet ex situ facilities are often constrained by feed ingredient availability when attempting to replicate natural diets. In obligate carnivores such as vultures, digestive strategies are likely to have evolved alongside feeding behaviors, which may differ between even sympatric species. To begin to understand the digestive strategies of two Old World vulture species (lappet-faced vulture Torgos tracheliotos, n = 3, and griffon vulture Gyps fulvus, n = 4) of similar body size but divergent feeding habits, their feeding and digestion strategies on a diet of whole rats were compared. The food intake, color of excreta, excreta consistency, and carbon and nitrogen excretion were measured. Mean retention time of the digesta was analyzed using titanium dioxide as an inert marker in a diet of chicken carcass. Lappet-faced vultures consumed significantly greater quantities of food than griffon vultures and were less selective. Lappet-faced vultures primarily produced brown excreta while griffon vultures primarily produced green excreta, with much higher carbon and nitrogen concentrations. The consistency of excreta and the mean retention time did not differ between the species but may have been too variable to detect differences. A strong positive correlation was found between food intake per metabolic weight and the proportion of brown excreta, and both were negatively correlated with green excreta, as well as excreta concentrations of nitrogen and carbon. These findings align with their reported feeding ecology, with lappet-faced vultures showing adaptations to less-digestible carcass material compared with griffon vultures. Despite their similar size and overlapping natural habitat, these results suggest a need for differentiated feed provisioning for these species when under human care.