New Descriptions, Intraspecific Variation and Systematic Importance of Drumming Behavior in Selected North American Plecoptera Page: 86

                                
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beat intervals (Table /, Figs. 43 and 44), and many of the
calls were made while on the run.
The one female answer consisted of two single beats
interspersed within the male call between the second and
seventh beats (Table V, Fig. 44).These two beats followed
the second and seventh male call beats by intervals of 120
and 125 msec, respectively. The interval between these two
female answering beats was 2167.0 msec.
I. montana drumming calls are closest to 1^. fulva
(Szczytko and Stewart 1979b; mean beats of 5.6±0.5 and beat
intervals of 160.4±14.2 msec). Female answers resemble I.
quinquipunctata (Szczytko and Stewart 1979b; whose answers
consist of mean 2.1±2.6 beats and also begin prior to the
completion of the male signal). These two species are
distributed in western North America, with no conceivable
range overlap or co-occurrence.
Isoperla ouachita -- Five males and two females were
tested at 23-25°C and 60 ftc, and 13 signals were obtained
from three, 1-day-old males. Their calls consisted of
rubbing beats, representing a newly discovered signalling
pattern among known Isoperla drumming. When amplified,
these recordings sound much like the croaks of cricket
frogs. The signals were successfully measured by playing
them at an extended (long play) mode from a Sony TC-142
cassette recorder onto the oscilloscope (compare Fig. 45 by
normal play with Fig. 46 by long play). The male calls had