THE GENERAL BIOLOQY OF PENQUINS
161
generally confined to areas with small annual temperature ranges, with
isothermal boundaries which are seldom transgressed. Thus Peruvian
penguins, breeding along a 2 000 mile (3 200 km) stretch of South
American Pacific coastline, live entirely within the Peruvian current at
temperatures which seldom depart from the annual range of 13-17°C.
Callao (12"S), close to their northern limit of breeding, and Valparaiso
(32"S), near the southern limit, differ in mean annual sea temperature
by only 1°C (Fig. 7). Beyond the inshore influences of the current lies a
fairly steep thermocline which would presumably be readily detectable
to temperature-sensitive homeotherms. Murphy has observed (1936,
p. 358) that South African Blackfooted penguins (an allied species with
parallel distribution in the Benguela current) in the New York Aquarium
are reluctant to enter their pool when the water temperature falls below
55°F (12-8°C). This suggests a degree of sensitivity sufficient to restrict
this species to its natural temperature environment of 12-16°C. Temperature ranges at Antarctic stations may be as low as 2°C annually:
penguins occupying the continental shore, Antarctic peninsula, Scotia
Arc and other islands within the Convergence, which together span over
20" of latitude in the circumpolar southern ocean, live in water which is
held throughout the year at almost constant temperatures by the
melting and freezing of ice.
Two-thirds of the areas listed in Fig. 7 have annual sea temperature
ranges of 65°C. Only two South American and one Australian station
have annual ranges exceeding 5°C. From many stations with higher
annual ranges migration is the expedient which allows breeding birds to
avoid one or other temperature extreme. Thus all penguins of the genus
Eudyptes spend their winters at sea; some, perhaps all, avoid the seasonal
fall in temperature by migrating northward with the isotherms. Magellanic penguins breeding on Valdez Peninsula (Patagonia) migrate a t the
end of their breeding season in May, probably to latitudes of Uruguay
and southern Brazil where they are frequently recorded as winter
visitors. They return to breed in September (Murphy, 1936, pp. 443445). This migration ensures that they remain within an annual sea
temperature range of about 4"C, 3°C less than the range for their breeding
area and 5°C less than for the Uruguayan coast (Fig. 9). Wandering birds
reported as far north as Cape Frio and Rio de Janeiro would in winter
be living in water only 2-3°C warmer than off Uruguay. Vagrants may
encounter wider ranges; thus an Ad6lie penguin captured on Macquarie
island in November (Gwynn, 1953, p. 150) and Emperors reported on
the Falklands in April (Hamilton and Roberts, 1954, p. 315) were in
water some 6°C higher than the species normally encounters.
Magellanic penguins on the Falkland Islands, in the coolest part of
their breeding range, feed in cool (5-6°C) but rapidly warming water on
161
generally confined to areas with small annual temperature ranges, with
isothermal boundaries which are seldom transgressed. Thus Peruvian
penguins, breeding along a 2 000 mile (3 200 km) stretch of South
American Pacific coastline, live entirely within the Peruvian current at
temperatures which seldom depart from the annual range of 13-17°C.
Callao (12"S), close to their northern limit of breeding, and Valparaiso
(32"S), near the southern limit, differ in mean annual sea temperature
by only 1°C (Fig. 7). Beyond the inshore influences of the current lies a
fairly steep thermocline which would presumably be readily detectable
to temperature-sensitive homeotherms. Murphy has observed (1936,
p. 358) that South African Blackfooted penguins (an allied species with
parallel distribution in the Benguela current) in the New York Aquarium
are reluctant to enter their pool when the water temperature falls below
55°F (12-8°C). This suggests a degree of sensitivity sufficient to restrict
this species to its natural temperature environment of 12-16°C. Temperature ranges at Antarctic stations may be as low as 2°C annually:
penguins occupying the continental shore, Antarctic peninsula, Scotia
Arc and other islands within the Convergence, which together span over
20" of latitude in the circumpolar southern ocean, live in water which is
held throughout the year at almost constant temperatures by the
melting and freezing of ice.
Two-thirds of the areas listed in Fig. 7 have annual sea temperature
ranges of 65°C. Only two South American and one Australian station
have annual ranges exceeding 5°C. From many stations with higher
annual ranges migration is the expedient which allows breeding birds to
avoid one or other temperature extreme. Thus all penguins of the genus
Eudyptes spend their winters at sea; some, perhaps all, avoid the seasonal
fall in temperature by migrating northward with the isotherms. Magellanic penguins breeding on Valdez Peninsula (Patagonia) migrate a t the
end of their breeding season in May, probably to latitudes of Uruguay
and southern Brazil where they are frequently recorded as winter
visitors. They return to breed in September (Murphy, 1936, pp. 443445). This migration ensures that they remain within an annual sea
temperature range of about 4"C, 3°C less than the range for their breeding
area and 5°C less than for the Uruguayan coast (Fig. 9). Wandering birds
reported as far north as Cape Frio and Rio de Janeiro would in winter
be living in water only 2-3°C warmer than off Uruguay. Vagrants may
encounter wider ranges; thus an Ad6lie penguin captured on Macquarie
island in November (Gwynn, 1953, p. 150) and Emperors reported on
the Falklands in April (Hamilton and Roberts, 1954, p. 315) were in
water some 6°C higher than the species normally encounters.
Magellanic penguins on the Falkland Islands, in the coolest part of
their breeding range, feed in cool (5-6°C) but rapidly warming water on