Ecological Patterns in Mammalian Vocal Frequencies: Evidence Across Body Sizes and Habitats

Jiya Shah, Tamanna Rathore, Anuradha Batabyal

Vocalisations in mammals are an important sensory modality that is used for various purposes in communication, courtship, territorial display, navigation, prey detection, predator avoidance, reproduction, and social coordination. These various call functions are differentiated from each other through certain properties. Call spectral properties are influenced by anatomical constraints, especially body size, and habitat characteristics. Such a bioacoustics phenomenon has been studied in only specific mammalian taxa without large-scale cross-species comparison. Our study aims to bridge that gap by comparing vocalisation frequencies in a representative sample of mammals across ecosystems. To understand the patterns of mammalian vocal frequencies across body sizes and habitats, we relied on two hypotheses. Allometric scaling hypothesis, suggesting that sound frequencies are influenced by body size due to constraints on the geometry of the vocal tract, lung pressure, and the frequency of the vocal fold vibrations. The acoustic adaptation hypothesis suggests that the nature of the habitat impacts vocal frequencies, and sound structure reflects the properties of the habitat. Additionally, the study also compares these variations across call functions and microhabitats. The results, in accordance with the hypotheses, demonstrate an inverse relationship between body size and vocal frequency. Smaller mammals (e.g., bats, rodents) produce higher-frequency sounds due to shorter vocal tracts and smaller resonating chambers. On the other hand, large mammals (e.g., elephants, whales) produce lower-frequency, long-wavelength calls that propagate farther. Subsequently, habitat modulates frequency differently depending on call functions. Aquatic mating calls are found to be higher-pitched, possibly due to clearer transmission in water, and aquatic social calls are lower in frequency compared to terrestrial mammalian call frequencies, consistent with low-frequency communication for group cohesion underwater. This study provides a large-scale comparison of representative mammalian species across body sizes and habitats to test the prevalent ecological hypothesis of acoustic adaptation and allometric scaling.