Sound transmission and burrow characteristics of the subterranean rodent Ctenomys talarum (Rodentia: Ctenomyidae)

Males of tuco-tuco Ctenomys talarum Thomas, 1898 use particular burrow's entrances to emit their territorial vocalization. Therefore we studied the internal structure of these entrances and the possible effect on the emission and propagation of airborne sounds. Externally, the burrow entrances used by tuco-tucos males to vocalize were characterized by the absence of sand mounds around their openings. Internally, most of the burrow's entrances consisted of a main, relatively straight, tunnel of 30-40 cm length, with a diameter of 5.7-6.4 cm. After passing through the burrow's entrance, the low-frequency components of an artificial signal played back inside the tunnel were not only less attenuated but also amplified (measured at 10-30 cm from the burrow opening). Therefore, the emission of territorial vocalizations inside the particular burrow's entrances may be considered as a complex adaptative behavior, in which burrow structure improves the signal emission and propagation. Moreover, this work also showed that C. talarum's territorial vocalization seems to be adequate for long, inter-burrow communication, since its physical characteristics (high amplitude and low main frequency) are concomitant with the frequencies that are better transmitted in the natural habitat of this species of subterranean rodent.