THE GENERAL BIOLOGY OF PENGUINS
159
1. Sea Temperatures
Mean sea temperatures experienced at the breeding grounds, and
probably within the feeding ranges of the breeding birds, vary from
23°C at the Galapagos Islands to -1°C or less in some Antarctic seas.
Only three species (including the two smallest) live where mean sea
temperatures exceed lS”C, only five (including the largest) where the
mean is below 0°C. Most species live in water with mean sea temperatures
between 3” and 15°C.
Penguins are most numerous south of the tropical convergence (Fig.
4). Near the tropics they are most abundant in, but are not entirely
restricted to, areas where water temperatures are lower than the latitudinal mean. Simpson (1946, p. 91) regards them as “all unquestionably
adapted to cool water” and argues the likelihood of their origin in an
environment sub-polar or sub-tropical rather than polar. This view has
prevailed against the earlier interpretation of Boubier (1919, p. 135) who
first drew attention to the close relation between cold currents and
penguin distribution, and assumed their Antarctic origin almost without
question.
In Simpson’s context the word “cool” is enlightening, but in a broader
sense it under-rates the achievement of a family which has accommodated
successfully to the coldest, and to all but the very warmest of the world’s
seas. Galapagos penguins thrive in sea water at a mean annual temperature of 23°C: the mean for the warmest areas of the equatorial Pacific
Ocean is only some 5°C higher. For Northern Blue penguins, the word
“cool” means 16 to 19°C off the coast of south-western Australia, and
Rockhopper penguins in different parts of their range live in waters at
temperatures from 18-2°C or less. At the Galapagos Islands the sea is
cooler than the latitudinal average, i.e. there is a latitudinal temperature
anomaly of -2°C to -5°C throughout the year. Off the Australian coast
the temperature anomaly is slightly negative in summer (OOC to -1°C)
about the penguin breeding areas, but equally positive in winter (Schott,
1935, pl. 25-26), and for Atlantic stocks of Rockhopper penguins the
annual anomaly is negative at Tristan da Cunha but positive a t the
Falkland Islands (Schott, 1926, p. 12).
Many aspects of penguin distribution cannot be explained by “coolness”, whether absolute or relative. Penguins are unknown at many
islands in the southern tropical oceans where temperatures are similar
to those of the Galapagos Islands or southern Australia. They would
astonish the world by appearing, even as vagrants, at any of the hundreds
of seemingly suitable island or continental coastal areas in the northern
hemisphere. The distribution of genera and species is anomalous;
southern Chile has one species of penguin, while southern New Zealand
has three in separate genera - a contrast the more remarkable for the
159
1. Sea Temperatures
Mean sea temperatures experienced at the breeding grounds, and
probably within the feeding ranges of the breeding birds, vary from
23°C at the Galapagos Islands to -1°C or less in some Antarctic seas.
Only three species (including the two smallest) live where mean sea
temperatures exceed lS”C, only five (including the largest) where the
mean is below 0°C. Most species live in water with mean sea temperatures
between 3” and 15°C.
Penguins are most numerous south of the tropical convergence (Fig.
4). Near the tropics they are most abundant in, but are not entirely
restricted to, areas where water temperatures are lower than the latitudinal mean. Simpson (1946, p. 91) regards them as “all unquestionably
adapted to cool water” and argues the likelihood of their origin in an
environment sub-polar or sub-tropical rather than polar. This view has
prevailed against the earlier interpretation of Boubier (1919, p. 135) who
first drew attention to the close relation between cold currents and
penguin distribution, and assumed their Antarctic origin almost without
question.
In Simpson’s context the word “cool” is enlightening, but in a broader
sense it under-rates the achievement of a family which has accommodated
successfully to the coldest, and to all but the very warmest of the world’s
seas. Galapagos penguins thrive in sea water at a mean annual temperature of 23°C: the mean for the warmest areas of the equatorial Pacific
Ocean is only some 5°C higher. For Northern Blue penguins, the word
“cool” means 16 to 19°C off the coast of south-western Australia, and
Rockhopper penguins in different parts of their range live in waters at
temperatures from 18-2°C or less. At the Galapagos Islands the sea is
cooler than the latitudinal average, i.e. there is a latitudinal temperature
anomaly of -2°C to -5°C throughout the year. Off the Australian coast
the temperature anomaly is slightly negative in summer (OOC to -1°C)
about the penguin breeding areas, but equally positive in winter (Schott,
1935, pl. 25-26), and for Atlantic stocks of Rockhopper penguins the
annual anomaly is negative at Tristan da Cunha but positive a t the
Falkland Islands (Schott, 1926, p. 12).
Many aspects of penguin distribution cannot be explained by “coolness”, whether absolute or relative. Penguins are unknown at many
islands in the southern tropical oceans where temperatures are similar
to those of the Galapagos Islands or southern Australia. They would
astonish the world by appearing, even as vagrants, at any of the hundreds
of seemingly suitable island or continental coastal areas in the northern
hemisphere. The distribution of genera and species is anomalous;
southern Chile has one species of penguin, while southern New Zealand
has three in separate genera - a contrast the more remarkable for the