They use echolocation to communicate and hunt, making sounds that travel underwater until they encounter objects, then bounce back, revealing their location, size, and shape. Whales make a wide variety of communicative sounds, and each pod has distinctive noises that its members will recognize even at a distance. All pods use effective, cooperative hunting techniques that some liken to the behavior of wolf packs. Resident pods tend to prefer fish, while transient pods target marine mammals. These different groups may prey on different animals and use different techniques to catch them. There appear to be both resident and transient pod populations of killer whales. Killer whales hunt in deadly pods, family groups of up to 40 individuals. Though they often frequent cold, coastal waters, orcas can be found from the polar regions to the Equator. They are known to grab seals right off the ice. They feast on marine mammals such as seals, sea lions, dolphins and even other whales, employing teeth that can be four inches (ten centimeters) long. Orcas, or killer whales, are the largest of the dolphins and one of the world's most powerful predators.