Fifteen species of cranes make up this distinct, worldwide family, which has no close relatives. Members of this group are large, walk slowly along the ground, and fly with their long necks fully extended. Outside of the nesting season, most cranes gather in large flocks. Many species are migratory and will migrate in large groups, resting at the same stopover sites year after year. The young do not know their migratory routes instinctively, and learn them from their parents and other adult birds. Cranes are long-lived birds, and many live for 20–30 years. Most are omnivores associated with wetlands. Pair bonds are monogamous and long-term, and both parents help raise the young. Cranes establish and maintain these pair bonds with elaborate courtship displays and dances. This is one of the most threatened families of birds in the world, with 11 of the 15 species vulnerable to extinction.