which we used to separate
syllables. The thresholds were the transition points between the
two distributions (the duration of least frequency in between the
two modes in the first case, or the duration of the beginning of the
abrupt increase in frequency in the second case). For the species in
which these juxtapositions of distributions were obvious (N ¼ 29
species), the calculated threshold was about half the length of the
average duration of intervals between syllables (hereafter, simply
intervals), and this ratio varied remarkably little across species
(standard deviation of threshold/mean duration of intervals
¼ 0.078). Therefore, for the remaining 15 species in which this
juxtaposition was not obvious, we calculated the threshold by
iteration so as to obtain the same ratio of threshold to intervals as in