Ultrasonic calling in 2 species of voles, Microtus pinetorum and M. pennsylvanicus, with different social systems

When isolated, pups of muroid rodents emit ultrasonic vocalizations, an indication that they are stressed by being alone and exposed to cooling temperatures. Rate of vocalizations is greatest at the end of their 1st week and beginning of the 2nd week, declines in the 2nd week as eyes open and thermoregulation becomes fully established, and ceases in the 3rd week. Young of 1 vole species, the prairie vole (Microtus ochrogaster), vocalize significantly more than those of other species, which has been attributed to the social structure of the species, because they have monogamous mating behavior and high level of biparental care. To determine whether this vocalizing behavior is typical of vole species with monogamous social systems, I examined calling behavior in another monogamous species with biparental care, the pine (or woodland) vole (M. pinetorum), and I compared it to that of a polygynous species that has only maternal care, the meadow vole (M. pennsylvanicus). Pups were isolated for 20 min at 22 degrees C +/- 2 degrees C and the number of ultrasonic calls they emitted was monitored. Pine vole pups vocalized at high rates, similar to prairie voles, emitting a mean of 47 calls/min at the ages when calling was greatest (8-16 days). In contrast, meadow vole pups vocalized significantly less, emitting a mean of 9 calls/min at the age of greatest calling (5-9 days). Pine voles continued vocalizing to 23 days, like prairie voles but different from other vole species, including meadow voles, which cease calling earlier. I conclude that young voles of monogamous species, which are highly affiliative and have paternal as well as maternal care, respond to the stress of isolation more strongly than do other vole species and emit more ultrasonic vocalizations than species that are less social and have less parental care.