Behavioral Selection of Coprophagy in an Arid-Adapted Herbivore: Does a Compatibility-Risk Gradient Shape Selective...

Coprophagy is widespread among herbivores but remains poorly understood in reptiles, where its ecological function has rarely been tested. We conducted controlled choice experiments with 25 adult Texas tortoises (Gopherus berlandieri), an arid-adapted hindgut fermenter, to determine whether feces consumption represents incidental ingestion or a selective behavioral strategy. Each tortoise was presented with six feces types representing self, conspecific, and heterospecific sources (feral hog (Sus scrofa), raccoon (Procyon lotor), coyote (Canis latrans), and nilgai (Boselaphus tragocamelus)). Coprophagy occurred in 96% of individuals, and both the probability and relative amount of consumption differed significantly among feces types. Tortoises showed a consistent preference hierarchy (e.g., self, conspecific, feral hog, raccoon, coyote, nilgai), providing evidence for a compatibility-risk gradient in which individuals favored feces most similar in dietary composition and microbial origin while avoiding those likely to pose digestive or pathogenic risk. These patterns suggest that coprophagy serves as a behavioral mechanism of nutrient recapture and microbial maintenance, sustaining fermentation efficiency in environments where microbial reservoirs are ephemeral. By selectively regulating microbial exposure, tortoises mitigate ecological constraints imposed by aridity and low nutrient availability. Our findings identify selective coprophagy as an adaptive behavior that links individual physiology with nutrient and microbial cycling in arid ecosystems, illustrating how behavioral flexibility promotes persistence in long-lived vertebrates inhabiting resource-limited environments.