Infant ultrasonic vocalizations and parental responses in two species of voles (Microtus)

When separated from conspecifics, the young of many rodent species produce ultrasonic vocalizations (USVs) that may facilitate parental approach. Ultrasounds were recorded from infants (0–14 days post partum) of two closely related species that exhibit different social systems, the montane vole (Microtus montanus) and the prairie vole (Microtus ochrogaster). Infant prairie voles emitted a greater number of USVs when isolated from conspecifics than did infant montane voles. Infant prairie voles also emitted a greater number of USVs in the presence of a parent than did infant montane voles. For both species, parental responses to individual infants were most rapid when pups were at those ages when they emitted the greatest numbers of USVs. Prairie vole parents approached pups most rapidly on days 6–8, whereas montane vole parents approached pups most rapidly on days 12–14. There were no differences between sires and dams of either species in their latencies to approach and contact pups. In general, however, infants of both species were retrieved more rapidly by dams than by sires. We suggest that differences in ultrasound production among vole species may correlate with differences in their species-specific social systems. It appears that the number of USVs produced by pups may vary with the amount of parent-pup contact typical of each species.