Graded calls of the smallest terrestrial mammal, the Etruscan shrew, living in a closed habitat.

Graded call types predominate in species inhabiting open habitats with complex social systems, whereas discrete call types predominate in species with simple social systems living in closed habitats. This study aims to establish the vocal repertoire of Etruscan shrews, the smallest terrestrial mammal, which lives in pairs in closed habitats. Through various behavioral experiments, vocalizations were recorded and analyzed using unsupervised soft clustering, identifying four call types, one of which exhibited gradation. These calls were present in both pups and adults, showing age-related acoustic differences. One call type was observed during socio-positive behavior, with higher call rates during female-male interactions, while the others occurred during socio-negative contexts, with higher call rates for animals housed in pairs. Delivering the first detailed insight into Etruscan shrew vocal behavior, we demonstrated that the smallest terrestrial mammal possesses graded and discrete call types, regardless of its social system and habitat.