Abstract
Vultures are central-place foragers and need to optimize their foraging behaviour to offset travel costs by increasing their energy gain. This process is more obvious in certain vulture species that do not feed their young by regurgitation and so must carry food items back to the nest. The Bearded Vulture Gypaetus barbatus is the only species with a bone-diet based. We analysed the chemical composition of bones and the age-related changes in their nutritive value to assess the differences in energy content between bones of differing age, body part and species. We found differences between specific anatomical parts, species and the age of the bones. Fresh bones contain 108% as much energy as fresh meat and, interestingly, dry bones retain 90% of the protein found in fresh bones. Dry femurs weighing 140 g retain enough protein to be comparable to 111 g of fresh meat, in energy terms. Compared to meat-eating species, the specialized osteophagous diet of the Bearded Vulture seems to have certain advantages. A better understanding of nutrient levels in food remains could help to improve theoretical foraging models, assist in conservation management, and even improve our understanding of the use of bones by early hominids.
Highlights
As the distance travelled to find food increases, central-place foragers should compensate for the increased travel costs by increasing the energy gain from the food collected[3, 4]
Knowing how bones retain their nutritive value over time has interesting implications for understanding Bearded Vulture ecology, will improve theoretical foraging models and the management and conservation of this threatened species, and provides tools to enable a better understanding of early hominid evolution
Our study revealed differences in fat and protein content between different anatomical parts, species, and bone age
Summary
As the distance travelled to find food increases, central-place foragers should compensate for the increased travel costs by increasing the energy gain from the food collected[3, 4]. A bone-based diet has the important advantage that bones remain edible for much longer periods than do soft tissues[13] This enables Bearded Vultures to effectively store bones at ossuaries, perches and nests[10, 11]. As central-place foragers, processing bones before carrying them to their young benefits Bearded Vultures by reducing the weight of food items and the energy required to carry them to the nest[14, 15]. They select the most nutritive, fatty parts of carcasses (those with a high percentage of oleic acid) regardless of bone size[15]. Knowing how bones retain their nutritive value over time has interesting implications for understanding Bearded Vulture ecology, will improve theoretical foraging models and the management and conservation of this threatened species, and provides tools to enable a better understanding of early hominid evolution
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