ULTRASONIC VOCALIZATIONS BY RAT PUPS - THE PRIMARY IMPORTANCE OF AMBIENT-TEMPERATURE AND THE THERMAL SIGNIFICANCE OF CONTACT COMFORT

We investigated the effects of isolation. huddling, and air temperature on ultrasound production by rat pups. Experiment 1 showed that ultrasound production by 8- to 9-day-olds was minimal at thermoneutrality and increased in response to small deviations of air temperature on either side of the thermoneutral zone. Experiments 2 and 3 showed that suppression of ultrasound production by contact with littermates is consistent with the thermal consequences of huddling. Experiment 4 showed that, contrary to previous conclusions, ultrasound production is not independent of ambient temperature in pups older than 10 days of age. Taken as a whole, these experiments emphasize (1) the importance of ambient temperature for the elicitation of ultrasound by rat pups of all ages studied. (2) the importance of the-mal factors in the suppression of ultrasound by littermate contact. and (3) the manner in which different methods can change interpretations of the behavior and physiology of infant rats.