Why do otters save rocks?

Otters store rocks because they are essential tools for their survival. Sea otters—the species most famous for this behavior—use these rocks as "anvils" to crack open hard-shelled prey like clams, mussels, and abalone.

They often keep a favorite rock tucked inside a loose pouch of skin under their forearm. This pouch acts like a pocket, allowing them to carry the stone with them while they swim or rest so they don't have to search for a new one every time they get hungry.

As for whether they have "favorite" pebbles: it certainly seems that way. Because otters have specific preferences for the size, shape, and weight of the rock that works best for their particular cracking technique, they tend to hold onto a stone they’ve bonded with. They will often use the same tool repeatedly for days or even weeks. It’s a clever bit of animal ingenuity—by keeping their favorite tool close, they save energy and make their mealtime much more efficient.