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seen in Fig, 4, each chirp ranges to the limits of the recording 
apparatus but has an intense band about 500 cycles wide slurring 
upward and downward many times between 1500 and 5000 Hz 
with a duration of 40-80 msec. Each slur is probably a small multi- 
ple acoustic effect of a short series of pegs on a resonating wing and 
the slurring effect probably is a function of pressure, velocity, and 
changing strike angle of the femoral ridge as it arcs along the pegs. 
Additional faint overtones are observed at 7 000 to 9000 Hz and 
12000 to 16000 Hz. They are not likely to be heard by human 
ears and probably are an artifact of the spectrograph (Watkins, 
1967). A sound between 3000 and 5000 Hz is usually picked up 
as approximating the tonal quality of the chirp. Chirps differ inter se 
in many ways and can be weak, strong, produced on the upstroke, 
downstroke, or both, high pitched, low pitched, etc. The average 
duration of a chirp is 60 msec and, when combined with other chirps 
in a phrase, has no standard interval. The sound intensity is difficult 
to measure directly, since the chirp is usually unitary and the 
Figure 4. Laboratory recording of chirps; the multiple chirps were at 
the beginning of a courtship sequence in which the male attempted to 
mount immediately, was repulsed at first, followed the female for nearly 
a minute giving unitary chirps and finally mounted and successfully 
copulated. The similarity of the peaks in the major (— fundamental) 
frequency band indicated that this is a single movement by both legs, 
either up stroke or down stroke. The “ghost” harmonics every 3-5 KHz 
probably indicates a basic spike pulse modulated by the number of pulses 
(= teeth on the intercalary vein) struck per sec/given instant (Watkins, 
1967), but this must be checked further. The unitary chirp and multiple 
chirps were selected separately and are not in any determined time relation 
to each other. 
Figure 5. Audiospectrogram of chipmunk ( Eutamias sp.) alarm cry. The 
fundamental frequency of this complex sound seems to be 1 to 8 KHz 
which to human ears would average a high grasshopper chirp of 5 KHz. 
Since grasshoppers probably are tone deaf, the amplitude (at greater 
distance), great directionality of the sound, its duration, and spacing could 
be a good mimic of the chirp, thus causing the orientation of the two males 
described in the text. 
Figure 6. Audiospectrogram of crepitation and squeal of two individuals 
in a caged population outdoors. The crepitation is separated from the 
squeal by two broad dark lines representing the landing of the insect on 
the wire netting. A smaller dark spot at about 1500 Hz represents a third 
impact on the wire. The squeal is difficult to reproduce clearly and is of 
much less amplitude than the crepitation and nearly the same as the back- 
ground air noises. However, the great variation in carrier frequency shows 
the basic pattern. The 5 ascending major frequency peaks may represent 
multiple strokes, but at present we cannot ascertain how many strokes are 
produced nor what mechanism modulates the pulse rate frequency. 
