Vocal dialects in parrots: patterns and processes of cultural evolution

Abstract

Vocal dialects have fascinated biologists for over 50 years. This mosaic pattern of geographic variation in learned vocalizations was first described in a songbird, and since that time, most studies investigating dialects have focused on songbird species. Here we examine patterns of geographic variation in the calls of a different group of vocal learning birds, the parrots (Order Psittaciformes). We summarize the growing literature on vocal variation in parrots, and complement this review with a survey of variation in the genus Amazona using calls from sound libraries. We find strikingly similar patterns to those previously found in songbirds. Over 90% of parrots examined in the literature, and 69% of Amazona species surveyed, showed geographic variation consistent with a propensity to share local call types. This trait is evolutionarily labile and widespread; within Amazona most clades contained species with and without geographic variation, and most major lineages of parrots include representatives with dialects. We found little support for the long-standing hypothesis that dialects isolate populations and thus generate genetic differences among populations. Instead, most studies support the idea that dialects are maintained by social benefits of matching local call types, a finding that has implications for the management of captive and endangered populations. Considerable scope remains for studies that experimentally test hypotheses for the exact nature of these benefits, as well as studies that employ comparisons among species, to understand how the interplay between ecology, social dynamics and vocal learning capacities produces different patterns of variation across the parrots.

Keywords: Psittaciformes; contact calls; cultural evolution; dialect; geographic variation; parrots.

Figure 1

Spectrograms demonstrating the complete spectrum of geographic variation in parrots, including; a) invariant calls in Thick-Billed Parrots, b) graded variation in Orange-Fronted Parakeets, and c) distinct mosaic dialects in Yellow-Naped Amazons. The labels indicate the names of the recording sites (in the case of Thick-Billed Parrots and Orange-Fronted Parakeets) or the dialects (Yellow-Naped Amazons). The distances shown represent the approximate flight distances between recording locations. For all species, the calls are presented from left to right in order from north to south. Orange-Fronted Parakeet calls were provided courtesy of J. Bradbury and S. Vehrencamp (Pocosol) or downloaded from www.Xeno-Canto.org (La Ensenada and Tarcoles).

Figure 2

Spectrograms illustrating two of the geographic patterns of vocal variation found a survey of contact calls of Amazona parrots. Panel a) illustrates a pattern of invariant calls in Amazona mercenaria, while b) illustrates variation consistent with the presence of vocal dialects in Amazona farinosa. For each species contact calls from 3 different sites are illustrated. All calls are isolated from recordings downloaded from the online sound library xeno-canto.

Figure 3

An ancestral state reconstruction of different classifications of geographic variation in the parrot genus Amazona based on a survey of recordings in sound libraries. Red lineages represent species classified as having geographic variation consistent with the presence of vocal dialects, blue lineages were classified as have invariant calls, and green lineages were classified as having hypervariable calls that made unambiguous classification of contact calls difficult. White lineages had insufficient sampling to classify them to a category of vocal variation.