166
B. STONEHOUSE
body length; pygoscelids, feeding mainly on euphausids, have relatively the shortest intestine, and fish-eating spheniscids have the
longest. Although some genera clearly favour particular kinds of food,
and may have minor adaptations for catching and digesting them,
penguins as a whole tend to be unspecialized feeders and probably take
whatever living food becomes plentiful from time to time. In captivity
they can be trained to take food from hand or bucket, but in the wild
seem to feed exclusively on prey moving in the water.
Several species reach their densest concentrations in waters noted for
massive seasonal production of fish or plankton, e.g. the Peruvian and
Benguela currents and rich whaling grounds of the Scotia Arc. The food
requirements of large breeding colonies are enormous, especially when
rapidly growing young are in the nest. Rjand (1960, p. 17) estimated that
a single Blackfooted penguin (weight 3.6 kg) takes on average 0.5 kg
of food daily for 185 days per year. The total population in South African
waters is therefore estimated to take each year over 5 million kg
of food - mostly shoaling fish - in competition with cormorants,
boobies, fur seals and commercial fishermen. Antarctic Addie penguins weighing over 5 kg may take about 2 kg of food per day when
feeding chicks at the height of the breeding season; thus the Laurie
Island colonies alone (p. 157) would require 10 million kg per day -
mostly of euphausids. Similarly the Rockhoppers of Gough Island
would daily remove about 6 million kg, and the Emperors of Coulman
Island about + million kg per day during their spring and summer
feeding.
These figures may be approximations within a factor of two or three,
but are not beyond the estimated capacity for production of rich sea
water within daily swimming distance of breeding grounds. Marr (1362)
estimated that at peak summer production, Euphausia superba (probably
the main food of pygoscelid penguins in the Bransfield Strait) can reach
concentrations of at least 29 g/m2 of surface water. Thus the total Laurie
Island population could feed daily in a circle of 11 km radius, i.e. within
7-8 miles (11-13 km) of the island. Within three hours’ swimming distance of the island, moving at a leisurely pace of 5-6 kt (8-10 km/hr),
the birds would find over seven times their daily food requirement,
which a current of 1 kt (considerably less than average for the area)
would replace every 36 hours. The Gough Island Rockhoppers, if capable
of a similar daily range, would require from the sea a productivity of less
than 4 g/ma. Competition with other species would reduce these margins
considerably, and some species, notably the pygoscelids, may at present
be benefiting by reduced competition following the slaughter by man of
many thousands of whalebone whales.
The following are known or believed to be important penguin foods:
B. STONEHOUSE
body length; pygoscelids, feeding mainly on euphausids, have relatively the shortest intestine, and fish-eating spheniscids have the
longest. Although some genera clearly favour particular kinds of food,
and may have minor adaptations for catching and digesting them,
penguins as a whole tend to be unspecialized feeders and probably take
whatever living food becomes plentiful from time to time. In captivity
they can be trained to take food from hand or bucket, but in the wild
seem to feed exclusively on prey moving in the water.
Several species reach their densest concentrations in waters noted for
massive seasonal production of fish or plankton, e.g. the Peruvian and
Benguela currents and rich whaling grounds of the Scotia Arc. The food
requirements of large breeding colonies are enormous, especially when
rapidly growing young are in the nest. Rjand (1960, p. 17) estimated that
a single Blackfooted penguin (weight 3.6 kg) takes on average 0.5 kg
of food daily for 185 days per year. The total population in South African
waters is therefore estimated to take each year over 5 million kg
of food - mostly shoaling fish - in competition with cormorants,
boobies, fur seals and commercial fishermen. Antarctic Addie penguins weighing over 5 kg may take about 2 kg of food per day when
feeding chicks at the height of the breeding season; thus the Laurie
Island colonies alone (p. 157) would require 10 million kg per day -
mostly of euphausids. Similarly the Rockhoppers of Gough Island
would daily remove about 6 million kg, and the Emperors of Coulman
Island about + million kg per day during their spring and summer
feeding.
These figures may be approximations within a factor of two or three,
but are not beyond the estimated capacity for production of rich sea
water within daily swimming distance of breeding grounds. Marr (1362)
estimated that at peak summer production, Euphausia superba (probably
the main food of pygoscelid penguins in the Bransfield Strait) can reach
concentrations of at least 29 g/m2 of surface water. Thus the total Laurie
Island population could feed daily in a circle of 11 km radius, i.e. within
7-8 miles (11-13 km) of the island. Within three hours’ swimming distance of the island, moving at a leisurely pace of 5-6 kt (8-10 km/hr),
the birds would find over seven times their daily food requirement,
which a current of 1 kt (considerably less than average for the area)
would replace every 36 hours. The Gough Island Rockhoppers, if capable
of a similar daily range, would require from the sea a productivity of less
than 4 g/ma. Competition with other species would reduce these margins
considerably, and some species, notably the pygoscelids, may at present
be benefiting by reduced competition following the slaughter by man of
many thousands of whalebone whales.
The following are known or believed to be important penguin foods: