Calls of the common loon are captivating and memory stirring. What would our northern and central Minnesota lakes be without this mournful cry and laughter of the wilderness? To appreciate loon calls you simply have to hear them in their natural setting. And as we listen, the variations of yodel, tremolo, wail, and other calls can tell us much about loon behavior.

The yodel-call, "oo-AH-ho," is used for territory advertisement and defense. It is given only by the male. The far-carrying wail-call, "ahaa-ooo-oooo-oooo-ooo-ahhh," is frequently used and helps the pair keep in contact with each other. This call is often heard at night and is considered the mournful cry of the wilderness.

The tremolo-call, a wild laugh, is probably the loon's all-purpose call and can signal alarm, worry or greeting. Usually the tremolo is coupled with a behavior response such as a dive, a run on the water surface or a takeoff, and it's the only call loons can give while in flight. The presence of people often evokes the tremolo, especially when boaters approach too closely. But we must remember, the tremolo isn't reserved just for intruding humans. Millions of years before people appeared the tremolo-call echoed across ancient lakes. Loon pairs frequently use a tremolo duet when something threatens their young. This splendid tremolo duet is also used in spring to reinforce pair bonds and to advertise territorial rights.

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.