  Timing features such as the silence gaps between vocal units -- inter-call
intervals (ICIs) -- often correlate with biological information such as context
or genetic information. Such correlates between the ICIs and biological
information have been reported for a diversity of animals. Yet, few
quantitative approaches for investigating timing exist to date. Here, we
propose a novel approach for quantitatively comparing timing in animal
vocalisations in terms of the typical ICIs. As features, we use the
distribution of silence gaps parametrised with a kernel density estimate (KDE)
and compare the distributions with the symmetric Kullback-Leibler divergence
(sKL-divergence). We use this technique to compare timing in vocalisations of
two frog species, a group of zebra finches and calls from parrots of the same
species. As a main finding, we demonstrate that in our dataset, closely related
species have more similar distributions than species genetically more distant,
with sKL-divergences across-species larger than within-species distances.
Compared with more standard methods such as Fourier analysis, the proposed
method is more robust to different durations present in the data samples,
flexibly applicable to different species and easy to interpret. Investigating
timing in animal vocalisations may thus contribute to taxonomy, support
conservation efforts by helping monitoring animals in the wild and may shed
light onto the origins of timing structures in animal vocal communication.
