Abstract
Squirrels are a diverse group in behaviour, morphology, and ecology. This variation is typified by the wide range of vocalizations spanning ground squirrels, tree squirrels, and flying squirrels. Squirrels produce calls that range in frequency, modulation, and function, with a complex set of social calls occurring across the family. We review the history of recording methods used in the description of squirrel vocalization repertoires, with emphasis on how the ecology and methodology impact the vocal ranges reported. The maximum, minimum, and dominant frequencies were considered against popular hypotheses that have attempted to explain the evolution of vocal range in terrestrial mammals. These hypotheses include body size, predator avoidance, sociality, and time partitioning. Phylogenetic generalized least squared modelling revealed that social complexity and open habitats were the strongest drivers of high-frequency communication, whereas body mass constrained the lower frequency limit of vocalizations. Additionally, nocturnality was significantly associated with high-frequency calls, suggesting that flying squirrels, the only nocturnal squirrels, commonly use high-frequency acoustic signals, a finding that merits further investigation. In conclusion, our review provides a unique insight into the role of behavioural ecology on vocal repertoires and the importance of accurate equipment selection for sampling across a diverse taxon.
Highlights
Mammalian bioacoustics is an expansive field in which biology, physics, and psychology are used to study the taxonomic diversity of signalers and interpret the complexity of vocal communication
We found that across the squirrel family, body mass significantly affected all frequency characteristics, a finding that is mostly consistent with other literature (Arch and Narins, 2008; Charlton and Reby, 2016; Martin et al, 2016)
Social squirrels used higher fundamental, dominant, and maximum frequencies which aligns with the predator-avoidance hypothesis (Arch and Narins, 2008)
Summary
Mammalian bioacoustics is an expansive field in which biology, physics, and psychology are used to study the taxonomic diversity of signalers and interpret the complexity of vocal communication. Calls in adult female yellowbellied marmots (Marmota flaviventris) are directly correlated to the emergence of juveniles (Blumstein et al, 1997) Primates, another group of highly communicative and socially variable mammals, trend toward increased vocal complexity and overall improved hearing sensitivities in more social species and larger groups (Ramsier et al, 2012). They suggest that forested animals may boost the amplitude and increase the frequency band of their calls to help counteract the increased attenuation of their environment and improve the ability of receivers to locate the sender (Charlton et al, 2019) This hypothesis would explain why squirrels in closed habitats continue to use high frequencies, despite the limitations. We conclude that the type of equipment being used is crucial for detecting all frequency characteristics and that using equipment with large bandwidths (the entire range of frequencies that could be detected) is important for all squirrel acoustics research as we continue to discover novel USV production in Sciuridae
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