Photoperiod, temperature and melatonin effects on thermoregulatory behavior in Djungarian hamsters.

Nesting and burrowing activity were measured in hamsters acclimated to either long or short day photoperiod in thermoneutrality and at 10 degrees C. Hamsters build larger nests under short day photoperiod or at 10 degrees C as compared to long day photoperiod or thermoneutrality. Both environmental cues contributed about 50% to a total increase in nest size from 1.8 g cotton/day to 7.7 g cotton/day (long day thermoneutral versus short day at 10 degrees C). Burrowing activity was suppressed by both cold or short day exposure. Daily melatonin injections, effective in inducing physiological short day adjustment under a long day photoperiod, also increased nesting scores. Hamsters which did not respond to short day conditions or to melatonin treatment physiologically lacked behavioral adjustments as well. Collectively, these results demonstrate analogies in the environmental control of physiological thermoregulatory adjustment and nesting behavior. Burrowing activity seems to be more related to reproductive needs than to thermoregulatory requirements in this hamster.