Hydroperla crosbyi. Eighty-four and 60 signals were obtained from four and three, 1–5 day old males and females, respectively, at 23°C and 58 FTC. Males and the females produced 2-way (N=56) and 3-way exchanges (N=4). The four males consistently called with two grouped (Bi-grouped) signals. The first group’s range in beat count from 2–4 contains one less and more than previously described by Zeigler & Stewart (1985). Treating the two call-groups separately, the first contained 3 mode beats (3.0 ± 0.4); with intervals of 45.8 ± 16.6 ms and the second group had 4 mode beats (3.6 ± 0.5); with intervals of 47.4 ± 5.0 ms. The intergroup interval between these groups was 157.7 ± 29.8 ms Overall, males called with two groups containing 7 mode beats (6.6 ± 0.7), with overall intervals of 46.7 ± 11.5 ms (Fig. 8, Table 3). The individual average call intervals of groups 1 and 2 gradually decreased from 47.4 ms (i1) to 40.2 (i3) and from 49.6 ms (i5) to 45.1 ms (i7) respectively (Table 4). Mode and mean number of beats per female answer signal were 4 and 5.0 ± 1.8; mean beat interval was 64.0 ± 10.4 ms. The ♂ - ♀ exchange interval was 246.8 ms ± 84.4 ms and the male response contained 6 mode beats (4.7 ± 1.5); with intervals of 84.9 ± 19.2 ms. The ♀ - ♂ exchange interval was 39.4.3 ± 48.3 ms.
Isoperla bifurcata. One hundred thirty-six and 130 signals were obtained from two and one, 2–8 day old males and female, respectively, at 23°C andIsoperla phalerata. Fifty and 28 signals were obtained from one, 1–2 day old male and female, respectively, at room temperature and normal incandescent light. The male and female produced 2-way sequenced signals and the male called with diphasic signals. The male called with 13 mode beats (12.8 ± 0.9); with intervals of 96.6 ± 16.6 ms during first phase and with 22 mode beats (22.2 ± 1.6); with 34.6 ± 5.7 ms during the second phase (Fig. 10, Table 3). The first phase average individual intervals decreased from 124.4 ms (i1) to 62.6 ms (i14) and the second phase gradually decreased from 51.3 ms (i1) to 31.0 (i16), then increased to 35.2 ms (i24) (Table 4). Mode and mean number of beats per female signal were 5 and 5.0 ± 1.0; average beat interval was 109.9 ± 27.7 ms. The ♂ - ♀ exchange interval was 301.0 ± 124.0 ms.
These results for I. phalerata (Table 3) and those from Sandberg and Stewart (2003) for I. fulva and I. mormona (Table 6) differ considerably in overall average intervals for the same three species reported by Szczytko and Stewart (1979) (Table 5). We propose here that their consistently smaller intervals for these three species and those of I. quinquepunctata are probably in large part due to calibration inconsistency in their oscilloscope compared with the probably more accurate calibration of our computer (Sandberg and Stewart 2003).
Isoperla sobria. This species from a new location was analyzed individually during 2001 and 2004. A total of 99 and 20 signals were obtained from two 3-11 day old males and females, respectively. Recording occurred at room temperature and normal incandescent light in 2001 and 23–24°C and 84 FTC in 2004. In both years, males and females produced 2-way sequenced signals with either the female answer signal following the call (N=12), or with the beginning answer beats interspersed within the males 2 nd (N=1), 3 rd (N=3), 4 th (N=3) and 5 th (N=1) interval. In 2001, the male called with 4 mode beats (3.7 ±0.8); with intervals of 159.1 ± 7.2 ms and in 2004, with 6 mode beats (5.2 ± 1.0); with intervals of 151.1 ± 5.8 ms (Fig 11, Table 3). The 2001 average individual intervals gradually decreased from 162.4 ms (i1) to 156.1 ms (i2), then increased to 163.1 ms (i4) (Table 4). The 2004 average individual intervals gradually decreased from 152.4 ms (i1) to 147.7 ms (i2), then increased to 154.6 ms (i6) (Table 4). The 2001 mode and mean number of beats per female answer signal were 1 and 1.1 ± 0.2; beat interval was 62.9 ms (N=1). The 2001 ♂ - ♀ exchange interval was 99.8 ± 5.6 ms for sequenced and overlapped duets. The 2004 female answer signals contained only a single interspersed beat and the ♂ - ♀ exchange interval was 112.8 ± 4.0 ms. These results agree well within reasonable expected variation, with those of Sandberg and Stewart (2003) and do not suggest a new dialect.
Isoperla quinquepunctata. One hundred seven and seventy-eight signals were obtained from one, 1-day old male and female respectively, at 21°C and normal incandescent lighting. The male and female produced long signals or “symphonies” (Szczytko and Stewart 1979) of repeating 2-way sequences (Range: 2–9), with either the typical female single answer beat following the call (N=69) (Fig. 12A), or with her answer beat(s) interspersed within the 1 st, 3 rd, 4 th, 6 th, 8 th, 11 th, 13 th or 15 th (N=2) male interval (Fig. 12B, first underlined duet). The male called with signals of 7 mode beats; with intervals of 173.6 ± 11.4 ms (Table 3). The average individual call intervals gradually decreased from 179.9 ms (i1) to 171.0 ms (i6), remained fairly uniform until (i15), then increased to 190.8 ms (i20) (Table 4). Mode and mean beats per female signal were 1 and 1.0 ± 0.2; mean beat interval was 924.5 ± 254.0. The ♂ - ♀ exchange interval was 98.0 ± 5.2 ms for sequenced and overlapped duets.
In our analyses, we treated the multiple 2-way sequences and overlapped duets individually, instead of the entire “symphony” (underlined duets, Figs. 12A–B). These duets were separated from one another by consistently longer intervals (279.5 ± 62.4 ms) than typical interbeat call intervals (173.6 ± 11.4 ms).
These results are consistent with Szczytko and Stewart (1979) in terms of general signal description and beats, but differ considerably in beat intervals (Table 5). We propose that our consistently larger overall-mean-interval differences were due to the inconsistencies between their oscilloscope calibration and our computer, explained above under I. phalerata.