First, for trilled portions of song, syllables are the units
that repeat to form the trill. Second, for nontrilled portions, syllables
are sound elements or groups of elements separated from
others by intervals larger than a threshold, whichwas calculated for
each species as follows. We plotted the frequency of all interval
lengths, which in most species originates a bimodal distribution
(when within-syllable intervals are common) or a juxtaposition of
two distributions with a point of abrupt increase in frequency for
the second distribution. These juxtaposed distributions are symptomatic
of two classes of intervals: shorter intervals too brief for
minibreaths, which we consider to occur within syllables, and
longer intervals in which minibreaths are likely to occur