. Bonner zoologische Monographien. Zoology. 48 Ambient temperature: Aestivation may even occur at Ta between 27° and 33 ° C (Bartholomew and Hudson 1960) and hibernation between — 5° and 25° C (Eisentraut 1956, Herter 1956), so that there is actually no range in Ta, in which torpor would be impossible. However, a particular Ta may play the role of a cue. For example, several tropical and subtropical bats do not enter lethargy if Ta is lower than 17° C. In these bats, Tb not lower than 17° C is a pre-condition for spontaneous arousal at low Ta (Kulzer 1965). Limits of Ta between 15° and 25 ° C
. Bonner zoologische Monographien. Zoology. 48 Ambient temperature: Aestivation may even occur at Ta between 27° and 33 ° C (Bartholomew and Hudson 1960) and hibernation between — 5° and 25° C (Eisentraut 1956, Herter 1956), so that there is actually no range in Ta, in which torpor would be impossible. However, a particular Ta may play the role of a cue. For example, several tropical and subtropical bats do not enter lethargy if Ta is lower than 17° C. In these bats, Tb not lower than 17° C is a pre-condition for spontaneous arousal at low Ta (Kulzer 1965). Limits of Ta between 15° and 25 ° C were also found for torpor in various other species (Bartholomew et al. 1970, Scholl 1974). The European hedgehog and hamster become lethargic easier at Ta 10° C than at 2° C or even than at — 8°C (Bartos 1960). Generally, a temperature preference exists for the onset of lethargy, even a preference for a special microclimate (Bats: Davis 1970). If readiness for hibernation is present (Herter 1956) the thermal preferendum may be adjusted to a low Ta. Accordingly, the depth of the sleeping nest below the ground, may be related to the seasonal Ta (Eisentraut 1956, Herter 1956). Poikilothermy during torpor: In different species hibernation begins with marked periodical fluctuations of Tb in a circadian rhythm (Strum- Tb. •f* Prephasei j i i i ( i | i 3 U 6 8 hours Fig. 28: Drop of body temperature during entrance into hibernation. Pe = Perognathus longimembris, 8 g, Ta 3° C (Bartholomew and Cade 1957), P = Perognathus hispidus, 40 g, Ta 11° C (Wang and Hudson 1970), Ta = Tamias striatus, 95 g, Ta 10° C (Wang and Hudson 1971), El = Eliomys quercinus, 190 g, Ta 4° C (Pajunen 1970), Cil = Citellus lateralis, 190 g, Ta 6° C (Twente and Twente 1965), Cit = Citellus tridecemlineatus, 200 g, Ta 4° C (Lyman and O'Brien 1960), Er = Erinaceus europaeus, 680 g, Ta 4° C (Suomalainen and Saarikoski 1970), Ma = Marmota monax, 1500 g, Ta 10° C (Lyman 1958), Ph = Phala
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