Geographic variation of three vocal signals in the Australian ringneck (Aves: Psittaciformes): Do functionally similar signals have similar spatial distributions?

In many animal species, chiefly birds and some marine mammals, the repertoire of acoustic communication signals represents learned features of the behavioural phenotype, acquired and transmitted across generations as cultural traditions. These signals often are found to vary spatially among sub-species or local populations (e.g., dialects), as well as among smaller social groupings (colonies, flocks, pods, clans). Moreover, within the whole repertoire of different vocal signals of a species there can be differences in the patterns of spatial variation from one type of vocalization to another. A previous study of birdsong, for example, showed that males had two different kinds of song, functionally differing and with discordant patterns of geographic variation. This, and other studies describing spatial distributions of different elements of a learned vocal repertoire, suggests a general hypothesis that functional differences among an ensemble of cultural traits may be manifest as differences in spatial variation. My extension of this hypothesis is that among such a suite of cultural traits those of similar function will tend to co-vary spatially. In this report, I use three vocalizations of a parrot species to test this hypothesis. I recorded vocalizations of the Australian ringneck (Platycercus (= Barnardius) zonarius), at 49 sites across three subspecies distributions and quantified variation in the acoustic features of their vocal signals. Two of the vocal signals have similar function and, according to the hypothesis, should follow similar patterns of spatial variation, whereas the third signal has a differing function and is not expected to vary spatially in concordance with the other two signals. These predicted patterns were substantially upheld.