Cooling rates and body temperature regulation of hibernating echidnas(Tachyglossus aculeatus)

Abstract

SUMMARY Echidnas (Tachyglossus aculeatus) are amongst the largest deep hibernators, but it is difficult to get them to hibernate normally under laboratory conditions. We measured body temperature (Tb)in 14 free-ranging echidnas using implanted data-loggers. Cooling during entry into hibernation bouts followed a Newtonian cooling curve, and conductances calculated from cooling curves were identical to those observed in cold exposed euthermic echidnas. Comparison with a reference soil temperature demonstrated that echidnas showed behavioural thermoregulation during hibernation; early in the hibernation season echidnas preferred to hibernate in cool areas, while during the coldest months they moved to warmer hibernacula, giving a preferred Tb in the range 8–10°C. Thermal buffering against excessive variation in Tb may be as important as maintaining a low Tb.

Rewarming rates and thermogenesis in hibernating echidnas

“…In only one case did we find a significant deviation from the specified calibration that required correction. One echidna (male 1E7C) was subsequently fitted with an activity logger (Minimitter Actiwatch) (Nicol et al, 2004), giving 6 months of concurrent T b and activity records. Meteorological data, including soil temperature data (T soil ) measured at a depth of 20 cm, was obtained from an Australian Bureau of Meteorology observation station on the field site within a few km of the animals.…”

“…1, excluding the periods of torpor or hibernation, the mean T b is 31.2 ± 1.3°C, the mean daily T b range is 2.4 ± 1.0°C, and 98% of the data lies between 28 and 34°C. The large daily variation in T b is associated with activity, with maxima of both normally occurring at night (Brice et al, 2002;Nicol et al, 2004).…”

“…On each occasion this was a single spike in T b on a warm day in February after the echidna had shown a pre-hibernatory reduction in T b . Entry into hibernation follows a reduction and then complete abolition of the daily activity cycle (Nicol et al, 2004).…”

“…Because it is very difficult to induce echidnas to hibernate in the laboratory, we have for the last 10 years concentrated on studying hibernation in echidnas in the field, by using implanted temperature data-loggers in free-ranging echidnas (Nicol and Andersen, 1996Nicol et al, 2004) and we have so far collected more than 39 echidna years of data from 14 animals. These data include a large number of arousals, and the principal aim of this paper is to investigate the rewarming rates of free-ranging animals under natural conditions and to compare these with published data from laboratory measurements.…”

Body temperature as an indicator of egg-laying in the echidna, Tachyglossus aculeatus

“…Animals were returned to their place of capture after recovery from surgery, and then radio-tracked at regular intervals to determine their location. An additional female echidna was fitted with an activity logger (Minimitter Actiwatch) (Nicol et al, 2004).…”