THE GENERAL BIOLOGY OF PENGUINS
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own, but more commonly occur in scattered groups “. . . with each nest
isolated from its neighbours, though all birds in any breeding place are
well aware of the presence and identity of other members of the community” (Richdale, 1957, p. 2). The same would probably be true of
Fjordland, Little Blue and Magellanic penguins. Snares Islands penguins
are probably the most northerly species which tends always to form
small colonies, with some of the energetic sociability of the southern
species.
3. Predators
Most adult penguins die at sea, probably from predation by large
carnivores. Marine conditions which support penguins are also attractive
to seals and whales. Fur seals (Arctocephalus sp.), sea lions of three
genera, and phocid seals of five genera, inhabit penguin waters and have
nearly all, at one time or another, been suspected of predation. The only
seal known to be a regular predator of penguins is the Leopard seal
(Hydrurga leptonyx), which ranges from the coast of Antarctica to about
45’5 but is probably most plentiful among pack ice. Leopard seals take
a variety of prey, including other seals, carrion, fish and squid: near
Antarctic and sub-antarctic islands they tend to feed mainly on penguins, especially those resident throughout winter (Stonehouse, 1960,
p. 53; Law and Burstall, 1956, p. 16).
Penguins do not feature among the main foods of fur seals (Bonner
and Laws, 1964, p. 73) except on Campbell Island, where the New
Zealand Fur seal Arctocephalus forsteri takes Rockhoppers in quantity
(Bailey and Sorensen, 1962, p. 57), and perhaps also at Macquarie Island
where the same species is currently expanding and taking increasing
numbers of Rockhoppers (Warham, 1363, p. 254; Csordas and Ingham,
1965). At Gough Island, Swales (1965, p. 32) saw A. t . tropicalis snapping
at penguins on the beach and harrying them in the water; at Macquarie
Island Hooker’s sea lion Phocarctos hookeri takes Gentoos on the beach
and in the water (Gwynn, 1953, pp. 12-13). Killer whales Orcinus orca
and smaller dolphins may take penguins, but positive evidence is lacking.
Even the smallest cetaceans would probably require larger or more
numerous prey as a staple diet, and their casual predation would hardly
be likely to affect penguin stocks seriously.
As equatorial and tropical penguins are among the few kinds of birds
which hunt by swimming (rather than plunging or diving), they would
seem especially vulnerable to sharks and the large predatory teleosts of
warm water. Hagen (1952, p. 35) considered the Blue shark Olyphis
(= Prionace) glaucus a possible predator of Rockhoppers on Gough
Island, but there are few records of shark or teleost predation from Africa,
South America or Australia. On the Galapagos archipelago, penguins
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own, but more commonly occur in scattered groups “. . . with each nest
isolated from its neighbours, though all birds in any breeding place are
well aware of the presence and identity of other members of the community” (Richdale, 1957, p. 2). The same would probably be true of
Fjordland, Little Blue and Magellanic penguins. Snares Islands penguins
are probably the most northerly species which tends always to form
small colonies, with some of the energetic sociability of the southern
species.
3. Predators
Most adult penguins die at sea, probably from predation by large
carnivores. Marine conditions which support penguins are also attractive
to seals and whales. Fur seals (Arctocephalus sp.), sea lions of three
genera, and phocid seals of five genera, inhabit penguin waters and have
nearly all, at one time or another, been suspected of predation. The only
seal known to be a regular predator of penguins is the Leopard seal
(Hydrurga leptonyx), which ranges from the coast of Antarctica to about
45’5 but is probably most plentiful among pack ice. Leopard seals take
a variety of prey, including other seals, carrion, fish and squid: near
Antarctic and sub-antarctic islands they tend to feed mainly on penguins, especially those resident throughout winter (Stonehouse, 1960,
p. 53; Law and Burstall, 1956, p. 16).
Penguins do not feature among the main foods of fur seals (Bonner
and Laws, 1964, p. 73) except on Campbell Island, where the New
Zealand Fur seal Arctocephalus forsteri takes Rockhoppers in quantity
(Bailey and Sorensen, 1962, p. 57), and perhaps also at Macquarie Island
where the same species is currently expanding and taking increasing
numbers of Rockhoppers (Warham, 1363, p. 254; Csordas and Ingham,
1965). At Gough Island, Swales (1965, p. 32) saw A. t . tropicalis snapping
at penguins on the beach and harrying them in the water; at Macquarie
Island Hooker’s sea lion Phocarctos hookeri takes Gentoos on the beach
and in the water (Gwynn, 1953, pp. 12-13). Killer whales Orcinus orca
and smaller dolphins may take penguins, but positive evidence is lacking.
Even the smallest cetaceans would probably require larger or more
numerous prey as a staple diet, and their casual predation would hardly
be likely to affect penguin stocks seriously.
As equatorial and tropical penguins are among the few kinds of birds
which hunt by swimming (rather than plunging or diving), they would
seem especially vulnerable to sharks and the large predatory teleosts of
warm water. Hagen (1952, p. 35) considered the Blue shark Olyphis
(= Prionace) glaucus a possible predator of Rockhoppers on Gough
Island, but there are few records of shark or teleost predation from Africa,
South America or Australia. On the Galapagos archipelago, penguins