Almost wholly aquatic, loons can swim long distances underwater and can dive from the surface to a depth of 60 metres (200 feet). Besides having solid bones, loons can further decrease their buoyancy for these dramatic dives by compressing air from their lungs, feathers, and internal air sacs. (Young loons, however, are buoyant and pop up like corks from their first attempts at dives.)

Loons feed mainly on fishes, crustaceans, and insects. The nest is usually a heap of vegetation at the water's edge, in which two (or, rarely, three) olive-brown spotted eggs are laid. The parents share the task of incubation. Parents often swim with the young on their backs. Loons are precocial birds; that is, they are well-developed at birth.

Common loons make a variety of calls, which carry long distances across water. A wail calls to and locates (by response) a missing mate. A “yodel” is given in aggressive defense of territory (each male has a different version of this call, which persists year after year.) A tremolo of 8–10 notes, resembling human laughter, is heard in spring in the loon's defense of territory or chicks. It is the only call made in flight and is frequently combined with other calls. Parents also hoot or “kwuuk” to chicks that may have strayed too far away.

Loon. (2011). Encyclopædia Britannica Ultimate Reference Suite.  Chicago: Encyclopædia Britannica.

http://en.wikipedia.org/wiki/Loon

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