“Body Temperature in Birds”, 1991 (; backlinks):
Mean levels of body temperatures (Tb) for all birds are (resting/active phase/high activity) 38.54 ± 0.96 (n = 203), 41.02 ± 1.29 (n = 724) and 43.85 ± 0.94℃ (n = 74).
Tb is higher in birds than in mammals: 1.87℃ higher during rest and 2.43℃ higher during the active phase.
As in mammals, the range of Tb-oscillation (day/night) decreases with increasing body mass. For birds 10–100,000g this range is 2.48–1.25℃.
Tb decreases slightly with increasing body mass. During the resting phase the correlation is not pronounced.
During the resting phase there is no marked difference in Tb between different taxonomic groups. Flightless birds and birds with high body mass show lower values during activity.
Slight nocturnal decrease in Tb (“hypothermia”) is shown in many birds as an adaptation to low food supply and/or heavy cold load.
Daily torpor is a special physiological ability. Tb may fall during the night to a minimum range of 18–20℃ with active rewarming. During “estivation” Tb may even fall to 4.5–7℃ without obvious ill effects.
Exogenous, artificial rewarming allows Tb to fall lower than normal torpor-levels.
Many other parameters are involved in the regulation of body temperature (circannual rhythms, hormones etc.).
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