188
B. STONEHOUSE
living at 60-70% above theoretical standard metabolic rate, probably
at lower air temperatures and for longer at a time than the Terre Addie
birds. Weight losses of incubating King penguins on South Georgia
suggest that metabolism remains at a high level (nearly 200% above
theoretical standard) throughout. This may be necessary for birds which,
in the absence of a recognizable nesting site or territory, remain alert to
defend their living space against the intrusions of late breeders (Stonehouse, 1960, p. 34). Heat losses are also likely to be high for this species
of thin plumage on South Georgia, one of its more southerly breeding
grounds.
Thus Kings in the sub-antarctic, and much smaller Addies in the
Antarctic, living a t different metabolic levels and in climatic conditions
of differing severity, each contrive to lose about 1 % of body weightlday
while fasting, a rate sufficiently low to allow them long periods ashore
for courtship and long incubation spells. Emperors solitary in the polar
winter also keep their daily weight loss close to 1%, although in much
colder conditions than Kings and Addies; more efficient insulation, a
more favourable surface-to-volume ratio, and reduced metabolic rate
and body temperature, probably all contribute to the achievement. By
huddling the loss is reduced to about 0.4% daily, allowing them the
much longer spell of starvation demanded by their winter breeding
routine.
Polar and sub-polar penguins lose weight twice as rapidly during
moult as in courtship and incubation; metabolic heat losses cannot be
calculated because an unknown proportion of energy is absorbed by
feather production. Richdale (1057, p. 175) suggests that losses of 4045% of original body weight occur in about four weeks in Kings, three
in species of intermediate size and two weeks in Little Blue penguins,
corresponding respectively to daily weight losses of 1.5, 2.0 and 3.0%.
This gradient may reflect the greater heat losses through comparatively
larger surface area of the smaller species, although some acceleration of
the replacement process is also evident.
B. HEAT BALANCE: S O M E CONCLUSIONS
Size, morphology, behaviour and ecology are all concerned in each
species’ attainment of heat balance. While present evidence is insufficient to show all the ways in which balance is achieved by all species,
the following tentative conclusions indicate some consistencies and
seeming inconsistencies which may in turn suggest further research.
Table I1 summarizes morphological evidence, i.e. the degree to which
the two main avenues of heat loss - short plumage and large flipper -
are possessed by each of the 24 listed species and sub-species of penguins
(data from Table I). Single and double signs indicate that the species lie
B. STONEHOUSE
living at 60-70% above theoretical standard metabolic rate, probably
at lower air temperatures and for longer at a time than the Terre Addie
birds. Weight losses of incubating King penguins on South Georgia
suggest that metabolism remains at a high level (nearly 200% above
theoretical standard) throughout. This may be necessary for birds which,
in the absence of a recognizable nesting site or territory, remain alert to
defend their living space against the intrusions of late breeders (Stonehouse, 1960, p. 34). Heat losses are also likely to be high for this species
of thin plumage on South Georgia, one of its more southerly breeding
grounds.
Thus Kings in the sub-antarctic, and much smaller Addies in the
Antarctic, living a t different metabolic levels and in climatic conditions
of differing severity, each contrive to lose about 1 % of body weightlday
while fasting, a rate sufficiently low to allow them long periods ashore
for courtship and long incubation spells. Emperors solitary in the polar
winter also keep their daily weight loss close to 1%, although in much
colder conditions than Kings and Addies; more efficient insulation, a
more favourable surface-to-volume ratio, and reduced metabolic rate
and body temperature, probably all contribute to the achievement. By
huddling the loss is reduced to about 0.4% daily, allowing them the
much longer spell of starvation demanded by their winter breeding
routine.
Polar and sub-polar penguins lose weight twice as rapidly during
moult as in courtship and incubation; metabolic heat losses cannot be
calculated because an unknown proportion of energy is absorbed by
feather production. Richdale (1057, p. 175) suggests that losses of 4045% of original body weight occur in about four weeks in Kings, three
in species of intermediate size and two weeks in Little Blue penguins,
corresponding respectively to daily weight losses of 1.5, 2.0 and 3.0%.
This gradient may reflect the greater heat losses through comparatively
larger surface area of the smaller species, although some acceleration of
the replacement process is also evident.
B. HEAT BALANCE: S O M E CONCLUSIONS
Size, morphology, behaviour and ecology are all concerned in each
species’ attainment of heat balance. While present evidence is insufficient to show all the ways in which balance is achieved by all species,
the following tentative conclusions indicate some consistencies and
seeming inconsistencies which may in turn suggest further research.
Table I1 summarizes morphological evidence, i.e. the degree to which
the two main avenues of heat loss - short plumage and large flipper -
are possessed by each of the 24 listed species and sub-species of penguins
(data from Table I). Single and double signs indicate that the species lie