Think Before They Squeak: Vocalizations of the Squirrel Family

Abstract

Squirrels (Sciuridae) are a diverse group in behavior, morphology, and ecology. This variation is typified by the wide range of vocalizations spanning ground squirrels (Marmotini and Xerini), tree squirrels (Callosciurinae and Sciurini), and flying squirrels (Pteromyini). 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 development of squirrel vocalization repertoires, with emphasis on how the ecology and methodology impact the frequency values reported. The fundamental (F 0 -the mean frequency of the fundamental harmonic), dominant (F Dom -the frequency of maximum energy or amplitude), minimum (F Min -the minimum frequency of the fundamental harmonic), maximum (F Max -the maximum frequency of the dominant harmonic), and highest harmonic (F Harm -the mean frequency of the highest visible harmonic) frequencies were considered against popular hypotheses that have attempted to explain the evolution of vocal frequency characteristics in terrestrial mammals. These hypotheses include body size, predator avoidance, habitat type, and diel activity pattern. Phylogenetic generalized least squared modeling revealed that body mass and the frequency limits of the methods were the strongest drivers of high-frequency communication. Consistent with popular hypotheses, social squirrels exhibited a broader range of F 0 , F Dom , and F Max than solitary squirrels while habitat openness promoted higher F Dom and F Harm . Additionally, nocturnality was significantly associated with higher F 0 , F Dom , and F Max , 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 behavioral ecology on vocal repertoires and the importance of accurate equipment selection for sampling across a diverse taxon.

Geographic variation in the matching between call characteristics and tympanic sensitivity in the Weeping lizard

“…These differences, however, disappeared when variables were corrected for body size; the southern population, with smaller body sizes, had calls with shorter duration, time to the maximum amplitude, and higher fundamental and dominant frequencies than the central population. The negative relationship between call frequencies and body size is similar to previous reports for different types of vocalization across taxa (Birds: Friis et al, 2021;Martin et al, 2011;Ryan & Brenowitz, 1985;Amphibians: Gingras et al, 2013;Tonini et al, 2020;Wilczynski et al, 1993;Crocodiles: Vergne et al, 2012;Mammals: Bowling et al, 2017;Newar & Bowman, 2020;Geckos: Rohtla Jr et al, 2019). It is not surprising this negative relation, considering that typically, larger animals have larger structures that result in the production of lower frequencies (Fletcher, 2004;Bowling et al, 2017;see Riondato et al, 2021 for an exception).…”

Gestational hypoxia in late pregnancy differentially programs subcortical brain maturation in male and female rat offspring

“…The more complex USVs, such as harmonic call types, are associated with sex behaviors, group housing, juvenile play, and other pleasurable behaviors (e.g., tickling) [50][51][52][53][54]. Larger USV bandwidths are associated with communicating to other rodents further away, indicating that the higher bandwidth may be used to compensate in a more expansive environment [55]. In addition to 50 kHz USVs, rodents vocalize at 22 kHz USVs under stressful of aversive conditions [56].…”

Structure and Function of the Vocalization of Japanese Squirrels, Sciurus lis

“…The acoustic structure of "kuk" sounds by the Japanese squirrel was similar to that of the chirp or the seet call of Tamiasciurus hudsonicus (Smith 1978;Greene and Meagher 1998). Newar and Bowman (2020), who examined the acoustic characteristics of 73 squirrel species, found that the fundamental frequency of sounds increased with decreasing body size. Smaller Japanese squirrels tended to produce a higher frequency "kuk" sound than other larger Sciurus species, which may be due to physical body size constraints (Fitch 2006;Newar and Bowman 2020).…”