On a hot, dusty afternoon in Africa's Etosha National Park, a group of elephants approaches a watering hole. They begin to drink and splash around. Suddenly, they freeze. One places her trunk flat on the ground, the tip pointing toward her feet. Soon, the elephants clump together defensively, nudging young calves into the center of the group. Some place weight on the front of their feet - as close to standing on tiptoe as elephants get. Most keep their huge ears flattened against their heads. Soon, they shuffle nervously away from the watering hole, staying in defensive formation.

Human observers nearby can't see or hear anything that might have alarmed the elephants. Researchers have noticed that elephant populations living elsewhere exhibit behaviors similar to those of the elephants at the watering hole. What are these elephants doing - and why? Look for clues in this chapter that explain the behavior of these elephant populations. Then, solve the mystery.