THE GENERAL BIOLOGY OF PENGUINS
187
reached while the birds are at sea, during the more active phase of their
lives. Although body temperature is generally ". . . the least variable
factor in the whole picture of homeothermy" (Scholander et al., 1950,
p. 247), variations of this order are not unusual in birds suffering heat
or cold stress: Howell and Bartholomew (1961, p. 193) found a core
temperature range of 36.2 (night) to 41-7"C (incubating in sun) in
Blackfooted albatrosses (Diornedea negripes) on Midway Island. King and
Farner (1961, p. 269, and Table X) report diurnal variations of 1 to 4OC
in several species, and the phenomenon may be more widespread than
was generally believed.
Temperature is maintained by metabolic heat production, which
varies with size, sex, activity a,nd (in some circumstances) temperature
gradient between body and environment. Standard metabolic rate (heat
production in unit time by it resting animal in standard conditions of
environmental thermoneutrality) may be calculated from the expression
log M = log 74.3 + 0.744 log W f 0.074
(King and Farner, 1961, p. 230), where M is the rate in kcallday and W
the weight in kg. Calculated values for all penguins appear in Table 11,
together with empirical values for two species calculated from data in
Scholander (1940, p. 127). Both empirical values are a little over double
the values calculated for the species, a discrepancy which cannot be
resolved without further data but is consistent with observ a t' ions on
marine mammals (Irvingand Hart, 1957; Kanwisher and Sundnes, 1966).
Metabolic rates of Antarctic and New Zealand penguins are currently
under investigation.
Weight losses recorded during incubation and other terrestrial activities of penguins provide some insight into their uses of stored energy.
Fasting birds are likely to be living entirely on fat reserves, providing
energy a t a rate of 9.5 kcallg. Emperors living sedentarily and in huddles
during winter, losing 120 g/day (p. 176), produce 1 140 kcall, i.e. live at a
rate some 14% above their theoretical standard metabolic rate. Emperors
sedentary but in captivity and unable to huddle, lose 330 g/day on
average (PrBvost and Sapin-Jaloustre, 1964, p. 72), indicating a metabolic rate some 200% above standard. About the same amount of energy
is consumed daily by active birds, newly returned from the sea, and
living on a mixed diet of protein arid fat.
Adelie penguins lost about 35 g/day during incubation in Terre Addie
(Sapin-Jaloustre, 1960, p. 145), indicating a metabolic rate some 2 6 2 5 %
above standard. Although in warmer conditions than incubating Emperors, they are more alert and aggressive and certainjy use more energy
in this phase of their breeding cycle. Addies losing 45-50 glday during
courtship and incubation a,t Cape Royds and Hope Bay (p. 176) were
187
reached while the birds are at sea, during the more active phase of their
lives. Although body temperature is generally ". . . the least variable
factor in the whole picture of homeothermy" (Scholander et al., 1950,
p. 247), variations of this order are not unusual in birds suffering heat
or cold stress: Howell and Bartholomew (1961, p. 193) found a core
temperature range of 36.2 (night) to 41-7"C (incubating in sun) in
Blackfooted albatrosses (Diornedea negripes) on Midway Island. King and
Farner (1961, p. 269, and Table X) report diurnal variations of 1 to 4OC
in several species, and the phenomenon may be more widespread than
was generally believed.
Temperature is maintained by metabolic heat production, which
varies with size, sex, activity a,nd (in some circumstances) temperature
gradient between body and environment. Standard metabolic rate (heat
production in unit time by it resting animal in standard conditions of
environmental thermoneutrality) may be calculated from the expression
log M = log 74.3 + 0.744 log W f 0.074
(King and Farner, 1961, p. 230), where M is the rate in kcallday and W
the weight in kg. Calculated values for all penguins appear in Table 11,
together with empirical values for two species calculated from data in
Scholander (1940, p. 127). Both empirical values are a little over double
the values calculated for the species, a discrepancy which cannot be
resolved without further data but is consistent with observ a t' ions on
marine mammals (Irvingand Hart, 1957; Kanwisher and Sundnes, 1966).
Metabolic rates of Antarctic and New Zealand penguins are currently
under investigation.
Weight losses recorded during incubation and other terrestrial activities of penguins provide some insight into their uses of stored energy.
Fasting birds are likely to be living entirely on fat reserves, providing
energy a t a rate of 9.5 kcallg. Emperors living sedentarily and in huddles
during winter, losing 120 g/day (p. 176), produce 1 140 kcall, i.e. live at a
rate some 14% above their theoretical standard metabolic rate. Emperors
sedentary but in captivity and unable to huddle, lose 330 g/day on
average (PrBvost and Sapin-Jaloustre, 1964, p. 72), indicating a metabolic rate some 200% above standard. About the same amount of energy
is consumed daily by active birds, newly returned from the sea, and
living on a mixed diet of protein arid fat.
Adelie penguins lost about 35 g/day during incubation in Terre Addie
(Sapin-Jaloustre, 1960, p. 145), indicating a metabolic rate some 2 6 2 5 %
above standard. Although in warmer conditions than incubating Emperors, they are more alert and aggressive and certainjy use more energy
in this phase of their breeding cycle. Addies losing 45-50 glday during
courtship and incubation a,t Cape Royds and Hope Bay (p. 176) were