A murmuration of starlings: reduced vocal diversity in more populous groups?
Résumé
Social evolution and vocal evolution may be strongly linked. The starlings are songbirds
known for their complex song repertoires and learning abilities. In the Red-winged Starling
(Onychognathus morio), variation in social organisation (territorial to more colonial breeding)
allows an assessment of the influence of social factors on vocal communication within a
single species. We compared the whistle characteristics among three populations with
different breeding associations in the Eastern Cape, South Africa. During one breeding
season, we recorded five widely-separated (>1 km apart) territorial pairs breeding in isolated
mountains, eight territorial pairs at higher density on a university campus (<100 m apart) and
two dense colonies on cliffs with nests <10 m apart. Our results show that each isolated
territorial pair had a large vocal repertoire and produced its own vocal themes. Conversely, as
the number of social partners increased, vocal sharing increased and the repertoire size was
reduced. The influence of habitat type and genetic differences between populations on vocal
variations was also investigated; the presence of more social partners seemed to be the key
factor inducing greater uniformity in vocalisations. In social groups, individuals in regular
contact need to use the same channel of communication to regulate their interactions. There
are interesting parallels with the evolution of language.