Animals defend territories to protect their assets such as food, water, or mates. Animals will also defend the area where their offspring live because in evolutionary terms, off-spring are the ultimate asset. Animals use pheromones—natural airborne or glandular chemicals that the animal releases—to mark their territory. This can be accomplished by leaving bits of fur, sweat, and dander on a visual object or by scent-marking with small amounts of urine. For example, outdoor cats rub pheromones from their face, paws, and leg glands against trees and other brush to leave a message to other outdoor cats that the area is their territory.