Individual signatures outweigh social group identity in contact calls of a communally nesting parrot

Abstract

Despite longstanding interest in the evolutionary origins and maintenance of vocal learning, we know relatively little about how social dynamics influence vocal learning processes in natural populations. The “signaling group membership” hypothesis proposes that socially learned calls evolved and are maintained as signals of group membership. However, in fission–fusion societies, individuals can interact in social groups across various social scales. For learned calls to signal group membership over multiple social scales, they must contain information about group membership over each of these scales, a concept termed “hierarchical mapping.” Monk parakeets (Myiopsitta monachus), small parrots native to South America, exhibit vocal mimicry in captivity and fission–fusion social dynamics in the wild. We examined patterns of contact call acoustic similarity in Uruguay to test the hierarchical mapping assumption of the signaling group membership hypothesis. We also asked whether geographic variation patterns matched regional dialects or geographic clines that have been documented in other vocal learning species. We used visual inspection, spectrographic cross-correlation and random forests, a machine learning approach, to evaluate contact call similarity. We compared acoustic similarity across social scales and geographic distance using Mantel tests and spatial autocorrelation. We found high similarity within individuals, and low, albeit significant, similarity within groups at the pair, flock and site social scales. Patterns of acoustic similarity over geographic distance did not match mosaic or graded patterns expected in dialectal or clinal variation. Our findings suggest that monk parakeet social interactions rely more heavily upon individual recognition than group membership at higher social scales.

Fine-scale genetic structure in the critically endangered red-fronted macaw in the absence of geographic and ecological barriers

“…The lack of actual genetic intermixing thus arises despite possible intermixing of flocks from different genetic clusters in non-breeding areas used temporarily, which indicates very limited effective dispersal leading to recruitment into non-natal genetic clusters. This can arise by individual recognition within social groups strongly attached to natal and breeding colonies in this species, which may be achieved through complex organisation and behaviour facilitated by informative vocalisations 78 and dialects common among parrots 16 , 17 , 79 .…”

Individual vocal signatures show reduced complexity following invasion

“…Native range contact calls were recorded in 2017 at nest sites in Uruguay, as previously described [11]. Invasive range contact calls were recorded at nest sites across five states in the U.S. over different years.…”

“…Models were built with 203 predictors, including 15 standard acoustic measurements and 188 features (Supplementary Methods 2.1.1). Spectrum-based measurements were obtained using a Hanning window, window length of 398, window overlap of 90 for Fourier transformations, and a bandpass filter of 0.5 to 9kHz [11]. 1561 calls were split into training, validation, and prediction datasets.…”

“…We asked whether the way in which vocal learning is employed for social recognition is resilient or sensitive to changes in population size by evaluating contact calls of an invasive parrot. Monk parakeets (Myiopsitta monachus) are native to South America, may use vocal learning for individual recognition [11], and have established invasive populations across the world through the pet trade [12]. We predicted that estimated social densities would be lower following invasion, and frequency modulation patterns in invasive range contact calls would be simpler compared to the native range.…”

Thinking Like a Parrot: A Wide‐Ranging Synthesis of the Current State of Research on Wild Parrot Biology

“…For example, the chapter on vocal communication generalizes the common (but not universal) patterns of call convergence we often find in wild parrot populations, where calls within pairs, groups, or regions tend to show similarities. An exception to this pattern has been documented in new research within wild Monk Parakeet ( Myiopsitta monachus ) populations, where individual call structures show a surprising lack of pair or geographic similarity, suggesting that the importance of individual identity and identification may outweigh benefits from signaling group affiliation (Smith‐Vidaurre et al 2020). Could this be evidence for a more individualistic societal organization for this species, compared to other parrots?…”