The perches are high in the trees, so other birds can see and hear it. Birds also sing to find a mate. The length and complexity of the mating song gives information about the fitness of the bird. Healthy birds can sing longer, more complicated songs. Birds call to one another in shorter vocalizations in order to warn of danger and to locate one another. Birds sing instinctively. Young birds learn to perfect their songs by listening to adult birds and interacting with other birds. Birds in a local area might learn variations in the basic song which help them recognize other members of their group.