For example, when wolves kill an elk, ravens and magpies arrive almost immediately. Many other animals benefit from wolf kills. In Yellowstone, 90% of their winter prey is elk 10–15% of their summer prey is deer. They efficiently hunt large prey that other predators cannot usually kill. Wolves consume a wide variety of prey, large and small. Research in Yellowstone since reintroduction has highlighted the adaptive value of social living in wolves – from cooperative care of offspring, group hunting of large prey, defense of territory and prey carcasses, and even survival benefits to infirmed individuals. Packs defend their territory from other, invading packs by howling and scent-marking with urine. The pack is a complex social family, with older members (often the alpha male and alpha female) and subordinates, each having individual personality traits and roles within the pack. In Yellowstone, average pack size is 11.8 individuals. Worldwide, pack size will depend on the size and abundance of prey. Wolves are highly social animals and live in packs. Wolves (back) are larger than coyotes (middle) and red foxes (front).