THE GENERAL BIOLOGY OF PENGUINS
165
Most penguins are sociable and tend to flock both on land and at sea.
Highly social species (especially of the Antarctic genera Aptenodytes and
Pygoscelis) have distinctive rallying calls which attract other members
of the species and facilitate flocking. Flocking behaviour benefits the
individual when food is plentiful but patchily distributed, when predators cannot be avoided except by cryptic behaviour, on migration (when
experience may be pooled), and in other special situations when the
group provides facilities which individuals lack. For most penguins the
advantages of flocking at sea are clear, and for many their terrestrial
environments are sufficiently remote or extreme to reduce dangers from
predators, parasites and pathogens, which usually accompanying flocking animals on land. Thus penguins flock and nest colonially on tropical
and sub-tropical guano islands, where populations are dense and nesting
space is restricted, and in polar regions where the group enhances its own
microclimate. For Emperor penguins incubating on sea ice in winter the
only shelter may be provided by the tight huddle of incubating birds;
individuals outside the huddle lose heat faster than those within (Stonehouse, 1953, p. 9; Prdvost, 1961, p. 60 and plates 1 and 6). Similarly
wind strength is reduced and air temperatures are raised within nesting
colonies of pygoscelid penguins (Yeates, in preparation).
The ecological significance of penguin behaviour on land has been
stressed in recent polar and sub-polar studies. If the needs of the marine
environment have dominated and moulded structural variability in
penguins, as flight has dominated morphology in other birds, additional
demands of the terrestrial environment have been met by modified
behaviour. Like flying birds, penguins vary behaviour rather than form
to solve or circumvent their ecological problems on land. So breeding
and social behaviour may differ widely between closely related species
of similar form, which occupy different land environments, e.g. such
congeneric and closely related pairs as Magellanic and Peruvian, Addlie
and Gentoo, King and Emperor, and Fjordland and Erect-crested
penguins.
c. FOOD, NEST SITES AND PREDATORS
1. Food
Penguins feed almost entirely on planktonic or nektonic animals: fish
(both larval and adult), crustaces and cephalopods predominate in
records of their feeding. Their beaks range in shape from fine forceps
(Aptenodytes) to powerful crushing pincers (Eudyptes); the tongue is short
and stiff, with retrorse spines, and the crop is usually a glandular sac, more
or less muscular a t the pyloric end but lacking marked specializations for
dealing with particular foods. Intestines vary disproportionately with
165
Most penguins are sociable and tend to flock both on land and at sea.
Highly social species (especially of the Antarctic genera Aptenodytes and
Pygoscelis) have distinctive rallying calls which attract other members
of the species and facilitate flocking. Flocking behaviour benefits the
individual when food is plentiful but patchily distributed, when predators cannot be avoided except by cryptic behaviour, on migration (when
experience may be pooled), and in other special situations when the
group provides facilities which individuals lack. For most penguins the
advantages of flocking at sea are clear, and for many their terrestrial
environments are sufficiently remote or extreme to reduce dangers from
predators, parasites and pathogens, which usually accompanying flocking animals on land. Thus penguins flock and nest colonially on tropical
and sub-tropical guano islands, where populations are dense and nesting
space is restricted, and in polar regions where the group enhances its own
microclimate. For Emperor penguins incubating on sea ice in winter the
only shelter may be provided by the tight huddle of incubating birds;
individuals outside the huddle lose heat faster than those within (Stonehouse, 1953, p. 9; Prdvost, 1961, p. 60 and plates 1 and 6). Similarly
wind strength is reduced and air temperatures are raised within nesting
colonies of pygoscelid penguins (Yeates, in preparation).
The ecological significance of penguin behaviour on land has been
stressed in recent polar and sub-polar studies. If the needs of the marine
environment have dominated and moulded structural variability in
penguins, as flight has dominated morphology in other birds, additional
demands of the terrestrial environment have been met by modified
behaviour. Like flying birds, penguins vary behaviour rather than form
to solve or circumvent their ecological problems on land. So breeding
and social behaviour may differ widely between closely related species
of similar form, which occupy different land environments, e.g. such
congeneric and closely related pairs as Magellanic and Peruvian, Addlie
and Gentoo, King and Emperor, and Fjordland and Erect-crested
penguins.
c. FOOD, NEST SITES AND PREDATORS
1. Food
Penguins feed almost entirely on planktonic or nektonic animals: fish
(both larval and adult), crustaces and cephalopods predominate in
records of their feeding. Their beaks range in shape from fine forceps
(Aptenodytes) to powerful crushing pincers (Eudyptes); the tongue is short
and stiff, with retrorse spines, and the crop is usually a glandular sac, more
or less muscular a t the pyloric end but lacking marked specializations for
dealing with particular foods. Intestines vary disproportionately with