Vocal development and patterns of vocal variation inform conservation of a critically endangered macaw

Reintroductions are increasingly used as a tool to bolster declining
populations of birds, but the potential for communication barriers arising
from learned vocal variation between introduced and wild populations has
rarely been considered. The critically endangered great green macaw, Ara
ambiguus, is one such declining species, but it is currently unknown
whether there is vocal variation in adult contact calls among
geographically isolated populations. Furthermore, variation in nestling
calls among populations has never been investigated and could offer
insight into how the nestling social environment shapes the formation of
dialects. We investigated whether adult and nestling great green macaws
show among-population variation in the acoustic structure of their calls
by recording vocalizations in one wild, one captive, and one reintroduced
population in Costa Rica. We assessed acoustic similarity among the three
populations by measuring 26 parameters from the spectrogram of each call
and performing spectrographic cross-correlation. We tested for population
differences in the acoustic structure of adult and nestling calls using
linear mixed models and Mantel tests. Only minimal variation was detected
among adult contact calls from the three populations. During
mid-development, nestling calls showed variation among populations that
may be explained by individual morphological differences and
overproduction of call types. Minimal variation later in development may
be explained by selective attrition of the vocal repertoire as well as
vocal convergence driven by the pressure to form and maintain flocks
during adulthood. Investigating adult and nestling calls across isolated
populations of threatened parrot species can give insight into how vocal
variation develops among populations and when conservation managers should
consider vocal differences between released and wild birds during the
reintroduction process.