Figure 1.

The effect of group size on pulse emission rates. (A) Bats' mean pulse emission rates recorded alone vs. when echolocating in pairs, and then again for alone vs. while echolocating with a speaker simulating the presence of another bat echolocating (playback). (B) Average emission rates per bat plotted vs. the total number of bats in the group. Pairwise multiple comparisons indicated that mean pulse emission rates for groups of 3 or more bats were significantly lower than solitary bat emission rates (Q = 5.033, p < 0.05). Data were fit with a first order linear regression (solidline, y = 0.92 + 3.82/x). (C) Plot of mean pulse rates vs. the rate at which overlaps occurred (interferences) for pairs (n = 141) and triads (n = 56) of bats. Both sets of data were well fit by the same simple power function of the form y = rτⁿ, where r = mean emission rate (Hz), τ = overlap window duration (ms) and n = number of bats. [r²= 0.71, F_{(1, 140)} = 344.9, P < 0.001]. Extending the functions derived from (C,D) illustrates the expected effect of pulse emission rates on mutual interference rates for groups of 2, 3, 5, and 10 bats. (E) These functions were then used to predict the effect of pulse emission rates on the proportion of pulses expected to generate unambiguous echoes, or y = 1 − rτⁿ (pulse efficiency) for different group sizes.