Hoot (short, single low note) 1. Given by males and females of all ages, beginning when babies are two or three months old. This is a contact call, usually given by an individual when it's approaching a group ("Hey--can I join you guys?") or by individuals within a flock, as during social gatherings ("What's up?) 2. "Cluck" similar to hoot given by parents to hatchign eggs or when chicks are about to enter the water, serving to encourage the babies. ("Good job! You can do it!)
Tremolo (sounds like the loon is laughing) 1. Given by males and females of all ages, beginning when babies are two or three months old. This is a distress call, which suggests that a loon is stressed, often before it escapes. ("Help!" or "Get me out of here!") In territorial disputes, the loon who is being chased is the one who most often gives the tremolo call. In defense of nests and chicks, loons give the tremolo call often while in the "penguin posture," an aggressive position, though after giving this call a few times, sometimes the loon flees. 2. When pairs give the tremolo call in a duet, it sometimes is a territorial statement. 3. Often given as a flight call, when approaching, leaving, or flying over a lake. The precise meaning of this call is not understood.
Wail (sounds similar to the howl of a wolf or coyote) Given by males and females of all ages, beginning when babies are in their first week. This is a contact call; when one loon gives it, the distance between that loon and another loon will soon be smaller. ("Come on over!") This call helps a young loon to bring its parent(s) closer, and helps an adult to bring its young and/or its mate closer.
Yodel (several upslurred introductory notes, similar to wails, and then loud repeated phrases) Given by males in spring and early summer, especially at night. The yodel is a territorial call Its purpose is to alert other males that this loon is defending a territory. ("This is MY lake!") Yodels are often answered by other males.