Northern cassowaries are one of the largest vertebrates in Papua New Guinea. They weigh between 25 and 50 kg and can be almost 2 m tall at their full height. They have glossy feathers with a shaggy texture. Their feathers are brown in young cassowaries and turn black by the time they reach maturity, at about 3 years old. Adult birds have a helmet-like casque, or hard structure, on the tops of their heads, the purpose of which is unknown. The most striking feature of northern cassowaries is the bright blue skin that covers most of its long neck and the bright red wattle under the beak. They have only one wattle, giving them the alternate common name, "single-wattled cassowaries." They have long and powerful legs and three toes with claws. There are negligible differences between males and females, leading many cultures of Papua New Guinea to believe only female cassowaries exist. The only noticeable difference is that females tend to be larger. There are no seasonal changes in the colors of cassowaries. However, when they become agitated, the colors on the neck and wattle deepen and they fluff out their feathers to appear bigger and more threatening.