THE GENERAL BIOLOGY OF PENGUINS
177
contribute significantly to weight losses, presumably because of the high
rate of water production in fat katabolism.
Mean body weights divide the contemporary species of penguins into
three well-defined groups. The smallest penguins are the Australasian
Fairy or Blue penguin, of which the Northern Blue may be slightly
smaller and lighter than its kin, and the White-flippered the heaviest.
Morphological differences between the four forms are slight and their
status is far from certain. Next in increasing size comes the Galapagos
penguin, for which published data are unfortunately meagre: they weigh
about 40 % heavier than Fairy penguins. Rockhoppers, weighing about
twice as much as Fairy penguins, lead in the middle-sized group of 13
species whose weights range between 3-5 and 6 kg. Of these the eudyptids
tend to be lightest at 3-4.5 kg, the spheniscids slightly heavier at 3-5 kg,
and the Yellow-eyed and pygoscelid penguins heaviest a t 4.5-6 kg.
Heaviest of all in the middle-sized range are the Northern Gentoos of
South Georgia and the Falkland Islands, which average a little over
6 kg.
King penguins are from three to five times the weight of the middlesized group; Emperors, largest of all, weigh twice as much as Kings, six
to nine times as much as the middle group, and nearly 30 times heavier
than the smallest penguins. In his survey of fossil penguins Simpson
(1946, pp. 75-76) lists seven species which, within understandably wide
limits of error, would fit the medium and small groups, one which might
bridge the gap between Gentoos and Kings, two of King size or slightly
larger, and seven Igiant” species of standing height 4-5 ft (120-150 cm).
Relations of mean weight to body temperature and metabolic rates
are discussed below.
b. Linear Dimensions
Body length is difficult to determine exactly in living or dead penguins
and its usefulness as an index of size is doubtful. Total length measurements including beak and tail are especially misleading in a metabolic
context, as beaks vary with species according to feeding requirements,
and rectrices are very long in some species (20% of body length in
pygoscelids), short in others. Girth measurements, whether axillary or
abdominal, vary with condition but are reasonably characteristic for
species, and useful with length measurements for defining body shape.
For volume and surface area calculations, which are necessarily approximate, I have found weights more reliable than linear dimensions, but the
relation between the two is currently under investigation. My present
rather inadequate data show that weight and body length (without
rectrices) approximate to the expected cube root relation (Fig. lob),
177
contribute significantly to weight losses, presumably because of the high
rate of water production in fat katabolism.
Mean body weights divide the contemporary species of penguins into
three well-defined groups. The smallest penguins are the Australasian
Fairy or Blue penguin, of which the Northern Blue may be slightly
smaller and lighter than its kin, and the White-flippered the heaviest.
Morphological differences between the four forms are slight and their
status is far from certain. Next in increasing size comes the Galapagos
penguin, for which published data are unfortunately meagre: they weigh
about 40 % heavier than Fairy penguins. Rockhoppers, weighing about
twice as much as Fairy penguins, lead in the middle-sized group of 13
species whose weights range between 3-5 and 6 kg. Of these the eudyptids
tend to be lightest at 3-4.5 kg, the spheniscids slightly heavier at 3-5 kg,
and the Yellow-eyed and pygoscelid penguins heaviest a t 4.5-6 kg.
Heaviest of all in the middle-sized range are the Northern Gentoos of
South Georgia and the Falkland Islands, which average a little over
6 kg.
King penguins are from three to five times the weight of the middlesized group; Emperors, largest of all, weigh twice as much as Kings, six
to nine times as much as the middle group, and nearly 30 times heavier
than the smallest penguins. In his survey of fossil penguins Simpson
(1946, pp. 75-76) lists seven species which, within understandably wide
limits of error, would fit the medium and small groups, one which might
bridge the gap between Gentoos and Kings, two of King size or slightly
larger, and seven Igiant” species of standing height 4-5 ft (120-150 cm).
Relations of mean weight to body temperature and metabolic rates
are discussed below.
b. Linear Dimensions
Body length is difficult to determine exactly in living or dead penguins
and its usefulness as an index of size is doubtful. Total length measurements including beak and tail are especially misleading in a metabolic
context, as beaks vary with species according to feeding requirements,
and rectrices are very long in some species (20% of body length in
pygoscelids), short in others. Girth measurements, whether axillary or
abdominal, vary with condition but are reasonably characteristic for
species, and useful with length measurements for defining body shape.
For volume and surface area calculations, which are necessarily approximate, I have found weights more reliable than linear dimensions, but the
relation between the two is currently under investigation. My present
rather inadequate data show that weight and body length (without
rectrices) approximate to the expected cube root relation (Fig. lob),