The Tremolo

   Reacting to the common loon's tremolo call, writer John McPhee 
reflected, "If he were human, it would be the laugh of the deeply 
insane." It's probably this call which drove the Chicago tourists out of 
their lakeside cabin. But getting a tremolo call on paper is like 
catching a brook trout with bare handsmit may be fun to try but one 
should not expect much for dinner. Barklow called the tremolo "a 
relatively slow frequency modulation with a superimposed 
modulation of amplitude." Then he got technical. It's a good thing we 
have the Voices of the Loon album and the opportunity to hear many 
thousands of the real callers. To appreciate the tremolo or any other 
loon call you simply have to hear it.

   While any motivational inferences about the tremolo are just 
informed guesses, Barklow and others have developed some well-
supported theories. After several years of attempting to put loon 
calls and behaviors together, Barklow has defined the tremolo as the 
loon's all purpose call which can signal alarm, annoyance, worry or 
greeting. Isolating three different types of tremolos, Barklow 
suggests the tremolo could provide a graded sytem of communication 
between loons. The lower frequency calls reflect a low level of 
anxiety or intensity while the high frequency tremolo calls reflect a 
sense of urgency. Barklow has designated these simply Types 1, 2 
and 3 with Type 1 being the lowest and Type 3 the highest level of 
intensity.

   According to Barklow, the ability to modify the "meaning" of a 
single call is rare in birds or other animals. Apparently loons can 
send very different messages by increasing the duration and 
frequency of the tremolo. The longest and most complex of the 
tremolo calls, the Type 3 call, is usually reserved for occasions of 
extreme alarm or anxiety.

   In Barklow's view, all three tremolo types usually signal a 
tendency to flee. Usually the tremolo is coupled with behavioral 
responses such as a dive, a run on the surface or a take-off. The 
presence of people often elicits the tremolo, especially when boaters 
or fishermen approach too closely. University of Stockholm scientists, 
Sverre Sjolander and Greta Agren, documented quite well this 
disturbance-tremolo association. From a distance they observed 
people encountering loons. In ninety-four consecutive human 
disturbance situations, loons gave a tremolo call; no other calls were 
heard.
   Mated pairs frequently use a tremolo duet when a disturbance 
threatens their young. When given "in stereo" on opposite sides of 
the intruder (like fishermen in a canoe) it can be very distracting 
and could potentially confuse less mentally gifted predators. This 
beautiful tremolo duet is also used in early spring to apparently 
reinforce pair bonds and advertise territorial rights.

   But the tremolo isn't reserved just for human encroachment. 
Millions of years before Homo sapiens appeared, the tremolo call 
echoed across ancient lakes. Loons often use the tremolo to 
communicate while flying; in fact, the tremolo is the only call loons 
can give while in flight. Loons are selective in their use of the 
tremolo when flying over lakes; Barklow noticed that loons flying 
over loon-less lakes were usually silent. Keeping track of when flying 
loons used the tremolo, Barklow heard tremolos only one of nine 
times a loon flew over a loon-less lake, but twenty-two of twenty-
four times a loon flew over a lake holding loons.

   Other situations which provoke the tremolo include, according to 
Barklow, the return of a loon's mate, social activities such as group 
displays, and chorusing with other loons. Attempting to relate the 
various tremolo types with particular loon behaviors, Barklow 
discovered that the Type 2 or middle ground call is the most 
versatile, accounting for over half of all tremolo calls. With the help 
of audiospectrographs, Barklow could even see subtle differences 
within call types. Some Type 2 calls reflect greater or lesser 
intensity. A low frequency Type 2 call might mean "let's get out of 
here" while a high frequency Type 2 might mean "let's get out of 
here now." These variations within variations give more meaning to 
Sigurd Olson's comment about an endless repertoire.