160
B. STONEHOUSE
many striking similarities of climate, topography and marine environment in the two areas. Five species breed on the Falkland Islands, but
only one on Tierra del Fuego less than 400 miles to the west.
The implication that cool water alone has food enough for penguins
is probably misleading. Discussing the distribution of Blackfooted penguins in southern Africa, Boubier (1919, p. 134) equated cold water and
wealth of plankton with their presence. Of the Benguela Current he
wrote “Les eaux froides venant de 1’Antarctique charrient avec elles une
masse Bnorme de plancton, agglombration des plantules et d’animalcules,
dont ces oiseaux se nourrissent”, and of the Agulhas Current - “Dans
ce courant chaud, pas de plancton et sur la cbte, pas de Sphhiscidbs.”
Neither statement is more than superficially true (Blackfooted penguins
eat fish rather than plankton, and are not uncommon in Agulhas waters
off southern Africa) and together they give a completely false impression
of penguin distribution. There are large seabirds enough on tropical
islands to show that pelagic food, although generally less abundant than
in higher latitudes, is far from scarce in warm water.
A more representative difference in distribution is that of Rockhopper
penguins on either side of the sub-tropical convergence in the southern
Atlantic Ocean. The Tristan da Cunha group, including Nightingale and
Inaccessible Islands, supports a total population of about 560 000 penguins which presumably feed in the tropical waters surrounding the
islands (Elliott, 1957, pp. 555-556). Gough Island, in sub-tropical waters
260 miles (416 km) to the south-east, has a population estimated at over
two million birds (Swales, 1965, p. 30).
Of the physical factors which could affect penguins in the seatemperature, density and salinity - only the first is likely to be significant in determining the range of individuals or species. Penguins of
nearly every species have been reported to swallow and regurgitate
pebbles in amounts which would adjust their specific gravity far beyond
the range of sea water densities likely to be encountered. Similarly, saltsecreting glands, nasal and superorbital, allow both polar and tropical
species to drink sea water in concentrations far greater than are normally
met even in the tropics (Schmidt-Nielsen and Sladen, 1958, p. 1216;
Douglas, 1964, p. 507). I n contrast, sea temperatures, which partly control heat losses in the submerged bird, vary widely with latitude and
current. Temperature variation over a short distance may tax the ability
of a species to acclimatize, and imprison it within the narrow span of
isotherms for which it is physiologically adjusted.
Many species of penguins, and most populations wihhin species, are
restricted geographically and seasonally to sea temperature ranges of
2 4 ° C . Although some individuals (notably juvenile or immature birds)
wander beyond their normal temperature limits, adult populations are
B. STONEHOUSE
many striking similarities of climate, topography and marine environment in the two areas. Five species breed on the Falkland Islands, but
only one on Tierra del Fuego less than 400 miles to the west.
The implication that cool water alone has food enough for penguins
is probably misleading. Discussing the distribution of Blackfooted penguins in southern Africa, Boubier (1919, p. 134) equated cold water and
wealth of plankton with their presence. Of the Benguela Current he
wrote “Les eaux froides venant de 1’Antarctique charrient avec elles une
masse Bnorme de plancton, agglombration des plantules et d’animalcules,
dont ces oiseaux se nourrissent”, and of the Agulhas Current - “Dans
ce courant chaud, pas de plancton et sur la cbte, pas de Sphhiscidbs.”
Neither statement is more than superficially true (Blackfooted penguins
eat fish rather than plankton, and are not uncommon in Agulhas waters
off southern Africa) and together they give a completely false impression
of penguin distribution. There are large seabirds enough on tropical
islands to show that pelagic food, although generally less abundant than
in higher latitudes, is far from scarce in warm water.
A more representative difference in distribution is that of Rockhopper
penguins on either side of the sub-tropical convergence in the southern
Atlantic Ocean. The Tristan da Cunha group, including Nightingale and
Inaccessible Islands, supports a total population of about 560 000 penguins which presumably feed in the tropical waters surrounding the
islands (Elliott, 1957, pp. 555-556). Gough Island, in sub-tropical waters
260 miles (416 km) to the south-east, has a population estimated at over
two million birds (Swales, 1965, p. 30).
Of the physical factors which could affect penguins in the seatemperature, density and salinity - only the first is likely to be significant in determining the range of individuals or species. Penguins of
nearly every species have been reported to swallow and regurgitate
pebbles in amounts which would adjust their specific gravity far beyond
the range of sea water densities likely to be encountered. Similarly, saltsecreting glands, nasal and superorbital, allow both polar and tropical
species to drink sea water in concentrations far greater than are normally
met even in the tropics (Schmidt-Nielsen and Sladen, 1958, p. 1216;
Douglas, 1964, p. 507). I n contrast, sea temperatures, which partly control heat losses in the submerged bird, vary widely with latitude and
current. Temperature variation over a short distance may tax the ability
of a species to acclimatize, and imprison it within the narrow span of
isotherms for which it is physiologically adjusted.
Many species of penguins, and most populations wihhin species, are
restricted geographically and seasonally to sea temperature ranges of
2 4 ° C . Although some individuals (notably juvenile or immature birds)
wander beyond their normal temperature limits, adult populations are