Wolves communicate with each other by howling.  Wolves live in packs that stake out large territories for hunting and raising families.  A pack of wolves likes to keep other packs out if its territory.  So one wolf pack howls at a neighboring pack, thereby warning it to stay away.

Members of a pack often howl to keep in touch with one another when they are hunting far apart.  Wolves sometimes howl together before they go hunting although no one knows exactly why.  But the popular belief that wolves howl at night, because they are lonely is not true.–Dick Rogers