The North American Beaver is the world's second-largest rodent, after the Capybara. Their large front teeth are used to cut trees, both for construction and for food. Beavers feed primarily on the underbark of various tree species. Their large, flat tails are used to warn other beavers of approaching predators; when a beaver is in danger, it will slap its tail repeatedly on the surface of its pond, creating a distinctive noise that is audible both above and below water. Beavers can hold their breath for as long as 15 minutes. They create ponds primarily to provide protection from predators. Beavers are monogamous and share ponds and lodges with their mates and offspring.