THE GENERAL BIOLOGY OF PENGUINS
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for want of precise information, has usually been neglected in discussions
of the biogeography and comparative ecology of the family. Yet small
warm-blooded creatures which spend weeks or months a t a time in water
(some in extremely cold water) must be strongly influenced by their
aquatic, as well as their terrestrial environment. As their source of food
the sea plays an important role in determining population size and
breeding seasons; it may also limit their distribution, and has certainly
dictated many details of their shape and form. Subjectively, penguins
seem more at home in the water than on land; much of their biology will
remain obscure until they have been studied more fully in their marine
environment.
The family Spheniscidae includes six clearly defined living genera, and
about 18 species of varying authenticity. Modern species range in weight
from less than one kg to a little over 40 kg, and in body length from 39 cm
to 115 cm. Feeding a t sea, but needing land for breeding and moulting,
penguins share with seals and other amphibious homiotherms the problem of maintaining constant body temperature, at a range of activity
levels, in two media of widely differing thermal capacity. Their body
temperatures on land are slightly lower than those of other birds of
similar size (King and Farner, 1961, p. 272), but may also be more
variable. In water, where penguins are most active, their body temperatures are probably higher than in other bird species. They float low in
the water and swim completely submerged at speeds of up to 12-15 kt
(6-8 mlsec). Migrant species remain in the water for three or four months
at a time and probably spend from half to three-quarters of their lives
at sea; others come ashore more frequently.
The largest penguin is some 15-20% shorter than the smallest adult
seal (Ringed seal Pusa hispida; Scheffer, 1958, p. 8) and less than half
its weight. Penguins are among the smallest aquatic homiotherms. Their
surface areas are comparatively large, and probably present some of
the most pressing problems in heat balance. No special adaptations for
deep or prolonged diving have been detected (Scholander, 1940, p. 84) -
nor would they be expected in birds which retain air between their
feathers for insulation while submerged. Skin and feather bases remain
dry even after long immersion. Penguins probably take most of their
food within 10 m of the surface, and seldom dive for spells of longer than
2-3 minutes. Swimming at speed they “porpoise” in and out of the
water, a method which allows them to breathe at regular intervals with
little loss of forward momentum.
The most striking morphological adaptations of penguins, i.e. the characters which distinguish them from all other birds, are those which fit
them for life in water. Elongate fusiform shape, upright stance, shootingstick tail, short limbs modified as paddles, plumage undifferentiated,
133
for want of precise information, has usually been neglected in discussions
of the biogeography and comparative ecology of the family. Yet small
warm-blooded creatures which spend weeks or months a t a time in water
(some in extremely cold water) must be strongly influenced by their
aquatic, as well as their terrestrial environment. As their source of food
the sea plays an important role in determining population size and
breeding seasons; it may also limit their distribution, and has certainly
dictated many details of their shape and form. Subjectively, penguins
seem more at home in the water than on land; much of their biology will
remain obscure until they have been studied more fully in their marine
environment.
The family Spheniscidae includes six clearly defined living genera, and
about 18 species of varying authenticity. Modern species range in weight
from less than one kg to a little over 40 kg, and in body length from 39 cm
to 115 cm. Feeding a t sea, but needing land for breeding and moulting,
penguins share with seals and other amphibious homiotherms the problem of maintaining constant body temperature, at a range of activity
levels, in two media of widely differing thermal capacity. Their body
temperatures on land are slightly lower than those of other birds of
similar size (King and Farner, 1961, p. 272), but may also be more
variable. In water, where penguins are most active, their body temperatures are probably higher than in other bird species. They float low in
the water and swim completely submerged at speeds of up to 12-15 kt
(6-8 mlsec). Migrant species remain in the water for three or four months
at a time and probably spend from half to three-quarters of their lives
at sea; others come ashore more frequently.
The largest penguin is some 15-20% shorter than the smallest adult
seal (Ringed seal Pusa hispida; Scheffer, 1958, p. 8) and less than half
its weight. Penguins are among the smallest aquatic homiotherms. Their
surface areas are comparatively large, and probably present some of
the most pressing problems in heat balance. No special adaptations for
deep or prolonged diving have been detected (Scholander, 1940, p. 84) -
nor would they be expected in birds which retain air between their
feathers for insulation while submerged. Skin and feather bases remain
dry even after long immersion. Penguins probably take most of their
food within 10 m of the surface, and seldom dive for spells of longer than
2-3 minutes. Swimming at speed they “porpoise” in and out of the
water, a method which allows them to breathe at regular intervals with
little loss of forward momentum.
The most striking morphological adaptations of penguins, i.e. the characters which distinguish them from all other birds, are those which fit
them for life in water. Elongate fusiform shape, upright stance, shootingstick tail, short limbs modified as paddles, plumage undifferentiated,