[Circadian and seasonal changes in the temperature-regulating behavior of the American ground squirrel Citellus parryi].

Under uninterrupted (during 10 days) temperature registration from 4 nest boxes ("thermogradient" plant) clear-cut changes were determined: in preferable temperature (PT, degrees C, in 24 hrs at an average)--21.0 +/- 0.5 (spring), 22.7 +/- 0.3 (summer), 18.8 +/- 0.7 (autumn), 11.5 +/- 0.5 (period before hibernation-PBH), 7.5 +/- 7.9 (hibernation season); in locomotor activity duration (LA, per cent from 24 hrs) which has decreased from 29.6% in spring to 20.3% at PBH (p < 0.001), and approximately to 2-3% during hibernation season; and in body mass which has varied from 350 g in spring to 750 at PBH. An increase in LA circadian rhythm amplitude was revealed in autumn, and the appearance and a rapid increase in PT circadian rhythm amplitude were observed at the beginning of PBH. A stage-to-stage "upswinging" of activity/rest circadian rhythms (stage I) and of thermoregulatory behavior (stage II) are supposed to occur at the end of euthermy season, which promotes synchronizing of the physiological processes and extending of the thermoneutra zone before the entrance into torpor and hibernation.