THE GENERAL BIOLOGY O F PENGUINS
169
Non-breeding or unoccupied Kings and Gentoos, which winter away
from the island, return to South Georgia beaches as food becomes
plentiful, and begin breeding soon after (Stonehouse, 1960, and in press).
Other species may anticipate the spring flush (e.g. probably Fjordland
penguins returning to southern New Zealand for breeding in July and
August, and Magellanic penguins returning to the Falklands in September) and rely on reserves of fat, gained elsewhere where food was plentiful,
to provide insulation and energy over a difficult initial period. Several
species (e.g. Rockhoppers on Macquarie, Antarctic pygoscelids) fast
during this period, when hunting may be only marginally profitable.
2. Nests and breeding habitats
King and Emperor penguins lay a single egg and hold it on their feet,
without any form of nest. All other species lay either two or three eggs
(those breeding for the first time may lay only one) and incubate them
in nests which, in site and form, vary characteristically between species.
Warmth for incubation is provided by the bare brood patch on the midline of the lower abdomen. Incubating Kings and Emperors crouch, with
a fold of loose abdominal skin wrapping over the egg. Smaller penguins
lie prone in the nest, usually with feet tucked under the eggs. Incubation
usually begins with the laying of the second egg. Eudyptid penguins lay
two (sometimes three) eggs of dissimilar size, of which generally the
larger one only is incubated.
All polar and sub-polar species breed colonially, usually on open ground
offering slight but not complete shelter from prevailing winds; lee areas,
which would fill with drift snuw in blizzards, are conspicuously avoided.
Toward temperate and tropical regions the species become less colonial
except on islands where numbers are high and suitable nesting stations
restricted. They tend to nest under cover - in burrows, caves, and the
interstices of tumbled rocks, and under dense tussock grass, shrubs or
fallen logs. South of the 60th parallel only Magellanic and Yellow-eyed
penguins nest in shelter; north of 46"s only the Tristan Rockhopper,
deprived of its natural tussock cover by browsing goatB, sheep and rats
(Elliott, 1957, p. 655), breeds in the open. Between 45 and 50"s Kings
and Macaronis retain their sub-Antarctic habit of nesting without shade
on Marion and Iles Crozet and Kerguelen; Gentoos and Rockhoppers
nest in the partial shelter of tussock grass; Snares Island penguins in
open forest or shade at the forest edge; Southern Blue and Yellow-eyed
penguins in caverns, hollows and under vegetation; Magellanics similarly
or in burrows.
The advantages of nesting under cover are various and may differ
in relative importance between species. Where thick tussock grass
(Nightingale and Gough Islands) or rain forest (southern Chile and
169
Non-breeding or unoccupied Kings and Gentoos, which winter away
from the island, return to South Georgia beaches as food becomes
plentiful, and begin breeding soon after (Stonehouse, 1960, and in press).
Other species may anticipate the spring flush (e.g. probably Fjordland
penguins returning to southern New Zealand for breeding in July and
August, and Magellanic penguins returning to the Falklands in September) and rely on reserves of fat, gained elsewhere where food was plentiful,
to provide insulation and energy over a difficult initial period. Several
species (e.g. Rockhoppers on Macquarie, Antarctic pygoscelids) fast
during this period, when hunting may be only marginally profitable.
2. Nests and breeding habitats
King and Emperor penguins lay a single egg and hold it on their feet,
without any form of nest. All other species lay either two or three eggs
(those breeding for the first time may lay only one) and incubate them
in nests which, in site and form, vary characteristically between species.
Warmth for incubation is provided by the bare brood patch on the midline of the lower abdomen. Incubating Kings and Emperors crouch, with
a fold of loose abdominal skin wrapping over the egg. Smaller penguins
lie prone in the nest, usually with feet tucked under the eggs. Incubation
usually begins with the laying of the second egg. Eudyptid penguins lay
two (sometimes three) eggs of dissimilar size, of which generally the
larger one only is incubated.
All polar and sub-polar species breed colonially, usually on open ground
offering slight but not complete shelter from prevailing winds; lee areas,
which would fill with drift snuw in blizzards, are conspicuously avoided.
Toward temperate and tropical regions the species become less colonial
except on islands where numbers are high and suitable nesting stations
restricted. They tend to nest under cover - in burrows, caves, and the
interstices of tumbled rocks, and under dense tussock grass, shrubs or
fallen logs. South of the 60th parallel only Magellanic and Yellow-eyed
penguins nest in shelter; north of 46"s only the Tristan Rockhopper,
deprived of its natural tussock cover by browsing goatB, sheep and rats
(Elliott, 1957, p. 655), breeds in the open. Between 45 and 50"s Kings
and Macaronis retain their sub-Antarctic habit of nesting without shade
on Marion and Iles Crozet and Kerguelen; Gentoos and Rockhoppers
nest in the partial shelter of tussock grass; Snares Island penguins in
open forest or shade at the forest edge; Southern Blue and Yellow-eyed
penguins in caverns, hollows and under vegetation; Magellanics similarly
or in burrows.
The advantages of nesting under cover are various and may differ
in relative importance between species. Where thick tussock grass
(Nightingale and Gough Islands) or rain forest (southern Chile and