First published online January 31, 2007
Journal of Experimental Biology 210, 586-592 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02701
Cooling rates and body temperature regulation of hibernating echidnas (Tachyglossus aculeatus)
Stewart C. Nicol* and
Niels A. Andersen
1School of Zoology, University of Tasmania, Private Bag 5,
Hobart, Tasmania, 7001, Australia and 2Discipline of Anatomy and
Physiology, University of Tasmania, Private Bag 24, Hobart, Tasmania, 7001,
Australia
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Fig. 1. Tb of male echidna 4572 during the 2000 hibernation
season (solid line) and reference soil temperature (Tref;
circles). Tb was measured at 96 min intervals by an
implanted data logger. Tref data were measured at a depth
of 20 cm at a Bureau of Meteorology station about 4.5 km from the centre of
the field site, and recorded daily at 09:00 h. Note the changes in
relationship between Tb and Tref that
occur at arousals 4, 6 and 8. The location of the hibernating echidna was
checked at the times marked by the arrows; it had moved 120 m between the
first and second observations, and 430 m between the second and third.
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Fig. 2. Tb data from four echidnas early in the 2000
hibernation season, illustrating how during hibernation Tb
tracks Tref (solid black line). One echidna (male 4572,
down-triangles) enters hibernation for the first time in the season on April
21, while another (female 006F, squares) shows her first periodic arousal on
April 27. Echidnas 006F and 1E7C (male, circles) entered hibernation on
February 12, while 2753 (female, up-triangles) entered hibernation on March 7.
All echidnas were hibernating in different locations up to 2 km apart.
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Fig. 3. Hibernating Tb for a male echidna (echidna 1E7C, mass
range 3.2–5.2 kg; A) plotted against reference soil temperature at a
depth of 20 cm (Tref) for five hibernating seasons, and
for a female echidna (echidna 006F, mass range 2.3–3.0 kg; B) for six
hibernating seasons. Solid lines are regressions fitted to all data. For
echidna 1E7C (A) Tb=0.65Tref+4.3,
r2=0.84; for echidna 006F (B)
Tb=0.62Tref+4.3,
r2=0.82. The fact that the slopes are significantly less
than 1 shows that at high Ta echidnas seek out cooler
areas to hibernate, while at low Ta they move to
relatively warmer areas.
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Fig. 4. Frequency distribution of Tb values from six echidnas
(five female, one male, black bars) and Tref (grey bars),
in May and July. In May the majority of Tref readings
(70%) were in the range 9–12°C, as were 70% of
Tb readings, but Tb values below
9°C are under-represented (4%) compared with Tref
(17%). In July the distribution of Tb values is
significantly offset compared with Tref. 58% of recorded
Tref values were between 6 and 8°C, but 62% of
Tb values were between 8 and 10°C.
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Fig. 5. Arousal events with subsequent re-entry into hibernation for two echidnas
(females 3A61 and 006F). (A) Tb (open circles) and
Tref (crosses and grey line). Solid black lines are the
regression lines calculated from the semi-log plots in (B). (B) Natural
logarithm of the adjusted Tb values
(Tb minus the equilibrium Tb) plotted
against time (h) from the start of the cooling episode. The solid line is the
linear regression through these data. r2=0.99 for both
regressions. The slope of the regression line is the cooling constant for the
animal (h–1) and the reciprocal of the cooling constant is
the time constant. For echidna 3A61, the time constant is 12.2 h, giving 36.6
h for 3 time constants or a 95% change. For echidna 006F, the time constant is
10.6 h, or 31.9 h for a 95% change.
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© The Company of Biologists Ltd 2007
