Data from: Differences in distress: variance and production of American crocodile (Crocodylus acutus) distress calls in Belize

Acoustic communication of American Crocodiles (Crocodylus acutus) is
relatively understudied. Our overall aim was to determine the acoustic
structure of wild American Crocodile distress calls, distinguish call
differences among size classes (hatchling, juvenile, sub-adult, and
adult), and investigate call production on a gradient of human
disturbance. American Crocodile distress calls have strong frequency
modulation and are comprised of multiple harmonics in a downsweeping
pattern. Measured parameters (total duration, first quartile duration,
maximal frequency, first quartile frequency, end frequency, slope of first
quartile, slope of last quartiles) differed significantly among size
classes (P < 0.05). Hatchling distress calls are higher in
frequency and strongly modulated, whereas calls produced by sub-adults and
adults showed little modulation, are lower in frequency, and have greater
overall duration. Proportion of crocodiles that produced distress calls
during capture differed by size class and sampling location, particularly
adult distress calls which are reported here to be produced with
undocumented frequency. We determined that American Crocodiles of all size
classes produce distress calls at varying rates among study sites. Our
results demonstrate that American crocodiles produce distress call more
frequently at sites with higher anthropogenic activity. Measured call
parameters of juveniles and hatchling American crocodiles also varied
among sites in relation to human disturbance. Calls recorded at sites of
high anthropogenic impact have increased duration and less modulation
which may adversely affect response to emitted distress calls.
Proportional and call parameter variances suggest anthropogenic activity
as a driver for increased call production and alteration of call
parameters at high human-impacted sites.