Biology, Development, and Ultrasonic Vocalizations of Bank Vole Infants

Abstract Bank voles are medium-sized rodents living mostly in forests with dense undergrowth. They reproduce from early spring to autumn with a pregnancy lasting from 18 to 21 days. Litters are not large, containing 1–8 pups. Bank vole pups can emit ultrasonic vocalizations from birth. The emission of these calls is maintained over the first 10 days of life and then gradually decreases until the emission stops at age 17–18 days, the time when juveniles leave the nest. In laboratory observations, the emission of pup ultrasonic calls was significantly increased by exposure to cold ambient temperature (18–20°C), or by absence of their mother without cooling. Pup vocalizations were also influenced by 2-h fasting in lower temperatures. The duration of individual ultrasonic calls was significantly longer when infants fasted. We conclude that cooling and fasting may independently increase calling. The emission of infantile ultrasonic vocalizations of bank vole pups was significantly decreased by reexposure to scents of the home bedding at 35–37°C, to the bedding of an alien lactating bank vole, or to a lactating mouse. Interestingly, ultrasonic calls in response to familiar bedding showed increased sound frequency.