Locomotion and postures of the Vietnamese pygmy dormouseTyphlomys chapensis(Platacanthomyidae, Rodentia): climbing and leaping in the blind

The Vietnamese pygmy dormouse is a small, arboreal, nocturnal, blind rodent that uses incipient echolocation to navigate in tree canopies. In order to assess its arboreal faculties in relation to echolocative capacity, the present study investigated the locomotor and postural behavior of the species in a simulated arboreal environment within an enclosure. The study subjects were intensively video and audio recorded and the two sets of data were synchronized for subsequent analyses. This is the first study on the positional behavior and substrate use of the Vietnamese pygmy dormice. Our results showed that the species spent most of its time on arboreal substrates, mostly traveling and scanning. Locomotion was dominated by vertical climb and leap, occurring mostly on small vertical and on medium and large strongly inclined substrates, respectively. Locomotion and substrate type were strongly related to emission of echolocative pulses. These findings most likely suggest that echolocation compensates for poor vision to effectively negotiate highly challenging arboreal constraints, and are in favor of the arboreal origins of pygmy dormice. Moreover, such a scenario could also support the echolocation-first hypothesis for the emergence of echolocation in bats prior to active flight.