186
B. STONEHOUSE
similarly likely to be small if the feather surface remains intact and the
insulating air is undisturbed. Moulting birds may suffer greater heat
losses in air while the plumage is incomplete, especially as the skin is
well vascularized while the feathers are growing; they are usually found
in well-sheltered corners away from the strongest winds, and do not
enter the water a t all until the new plumage is complete.
In calm air and strong direct sunlight polar and sub-polar species
show symptoms of overheating. Addlie penguins at Cape Royds gape
and respire rapidly at temperatures down to -4°C (measured in shade
close by) when exposed to full sun during incubation (Yeates, in preparation). In these circumstances the dark dorsal plumage is warmed to a
degree which, by reducing or locally reversing the body-to-air temperature gradient, may inhibit facultative heat shedding through the plumage. Birds moving freely in the colony stand with flippers slightly
extended, shedding heat freely through the exposed inner surfaces of
the flippers and feet. In temperate and tropical regions overheating
through insolation is likely to be a more serious problem, especially
where no shade is available for incubating birds. The large flippers of
some tropical and temperate species are believed to be significant in
this context (p. 180).
2. Temperatures, Metabolic Rates and Weight Losses
Core temperatures of homeotherms represent a balance between heat
production and losses to the environment. Low body temperatures imply
either low metabolic rates or rapid heat losses, e.g. from poor insulation,
high body-to-air temperature gradients, or (possibly) unfavourable
surface-to-volume ratios.
Mammal core temperatures vary little with body size. In birds, increasing heat production per unit weight tends to outstrip heat losses as size
decreases; small birds consequently have higher body temperatures than
large ones. McNab (1966, p. 48) established the relation T = 14.3W-0'00
+ 32-2, from which body temperature T"C may be derived when weight
W gm is known. Penguin body temperatures tabled by McNab range
from 37-7°C (King) to 39°C (Blue), and with one exception (Emperor
37.9"C) fall from 0.5 to 1.5"C below theoretical values predicted from the
expression.
However, Guillard (1 963; quoted in Prdvost and SapinJaloustre, 1964,
p. 71) and other French observers have recorded core temperatures
varying between 33 and 38-6°C in Emperors on land at different stages
of the breeding cycle, and between 36.3 and 40.3"C in Ad6lies. Emperors
reach their lowest core temperatures (34.6 & 1.86"C) while huddling
during incubation in April and May, Addlies while incubating or resting.
Higher temperatures in the range of McNab's curve would probably be
B. STONEHOUSE
similarly likely to be small if the feather surface remains intact and the
insulating air is undisturbed. Moulting birds may suffer greater heat
losses in air while the plumage is incomplete, especially as the skin is
well vascularized while the feathers are growing; they are usually found
in well-sheltered corners away from the strongest winds, and do not
enter the water a t all until the new plumage is complete.
In calm air and strong direct sunlight polar and sub-polar species
show symptoms of overheating. Addlie penguins at Cape Royds gape
and respire rapidly at temperatures down to -4°C (measured in shade
close by) when exposed to full sun during incubation (Yeates, in preparation). In these circumstances the dark dorsal plumage is warmed to a
degree which, by reducing or locally reversing the body-to-air temperature gradient, may inhibit facultative heat shedding through the plumage. Birds moving freely in the colony stand with flippers slightly
extended, shedding heat freely through the exposed inner surfaces of
the flippers and feet. In temperate and tropical regions overheating
through insolation is likely to be a more serious problem, especially
where no shade is available for incubating birds. The large flippers of
some tropical and temperate species are believed to be significant in
this context (p. 180).
2. Temperatures, Metabolic Rates and Weight Losses
Core temperatures of homeotherms represent a balance between heat
production and losses to the environment. Low body temperatures imply
either low metabolic rates or rapid heat losses, e.g. from poor insulation,
high body-to-air temperature gradients, or (possibly) unfavourable
surface-to-volume ratios.
Mammal core temperatures vary little with body size. In birds, increasing heat production per unit weight tends to outstrip heat losses as size
decreases; small birds consequently have higher body temperatures than
large ones. McNab (1966, p. 48) established the relation T = 14.3W-0'00
+ 32-2, from which body temperature T"C may be derived when weight
W gm is known. Penguin body temperatures tabled by McNab range
from 37-7°C (King) to 39°C (Blue), and with one exception (Emperor
37.9"C) fall from 0.5 to 1.5"C below theoretical values predicted from the
expression.
However, Guillard (1 963; quoted in Prdvost and SapinJaloustre, 1964,
p. 71) and other French observers have recorded core temperatures
varying between 33 and 38-6°C in Emperors on land at different stages
of the breeding cycle, and between 36.3 and 40.3"C in Ad6lies. Emperors
reach their lowest core temperatures (34.6 & 1.86"C) while huddling
during incubation in April and May, Addlies while incubating or resting.
Higher temperatures in the range of McNab's curve would probably be