Final answer:
The term 'telltale' in the provided context means 'revealing', as it refers to signs that clearly indicate the presence or behavior of grizzly bears.
Step-by-step explanation:
In the context provided, the term telltale most nearly means revealing. Wildlife biologists studying grizzly bears observe various signs such as tracks, claw marks on trees, and droppings along trails that reveal the presence or behavior of these animals.
Hence, the signs are considered telltale because they give biologists clear indications of grizzlies' activities without actually seeing the bears themselves.