THE GENERAL BIOLOGY OF PENGUINS
191
This evidence would be consistent with the view that plumage length,
on the whole a conservative character within genera, is determined
primarily by sea temperature, ideally increasing isometrically with body
size from smallest to largest genera, and deviating radically only at the
requirement of extreme conditions on land. Thus the spheniscids, with
uniformly thin plumage, seem adapted primarily for warmer water than
eudyptids and may have originated in the warm temperate or subtropical
zones. Extreme conditions on land have shortened the plumage of the
two species which experience the warmest environments, i.e. Galapagos
and Peruvian penguins. The plumage of Magellanic penguins is not correspondingly lengthened because this species, although inhabiting the
coolest range, remains in warm water throughout winter (p. 161) and
breeds in the shelter of burrows or dense vegetation in summer.
Similarly the eudyptids may have evolved in cool temperate waters,
in which they are at present most prominent, and by migration contrive
to remain in fairly constant environmental temperatures throughout the
year. Extremes of terrestrial climates are experienced by Macaronis and
Erect-crested penguins, but neither species winters in its breeding area
and neither has found a radical alteration of plumage length necessary.
The conservatism of eudyptids may arise from their use of superciliary
plumes as decoration. Small changes in length of the body plumage,
under a simple genetic control, may necessarily be accompanied by
radical and possibly disgenic changes in length of superciliary plumes.
Penetration of Antarctica has by contrast necessitated considerable
plumage lengthening in Adblies and Southern Gentoos. Future studies
may suggest why a similar change was not found necessary by Chinstraps. In the genus Aptenodytes the short plumage of the King may
represent an ancestral condition (necessitating an inflection in the
regression curve) from which Emperors, like Adblies, have deviated.
It could similarly be argued that variations in flipper area are primarily
determined by condition8 on land, although here the evidence is less
conclusive within genera, and further studies are required. The precise
role of the flipper as a radiator of surplus heat has yet to be defined in
a range of species from warm and cool environments, although the
circumstantial evidence already presented is sufficient to establish a
case for further study.
ACKNOWLEDGMENTS
I thank the Directors of the following museums for allowing me to
examine specimens in their keeping: American Museum of Natural History, British Museum (Nat. Hist.), Museum d’histoire naturelle, West
Australian Museum, Dominion, Canterbury and Okago Museums. This
work was assisted by grants from the Chapman Memorial Fund and the
191
This evidence would be consistent with the view that plumage length,
on the whole a conservative character within genera, is determined
primarily by sea temperature, ideally increasing isometrically with body
size from smallest to largest genera, and deviating radically only at the
requirement of extreme conditions on land. Thus the spheniscids, with
uniformly thin plumage, seem adapted primarily for warmer water than
eudyptids and may have originated in the warm temperate or subtropical
zones. Extreme conditions on land have shortened the plumage of the
two species which experience the warmest environments, i.e. Galapagos
and Peruvian penguins. The plumage of Magellanic penguins is not correspondingly lengthened because this species, although inhabiting the
coolest range, remains in warm water throughout winter (p. 161) and
breeds in the shelter of burrows or dense vegetation in summer.
Similarly the eudyptids may have evolved in cool temperate waters,
in which they are at present most prominent, and by migration contrive
to remain in fairly constant environmental temperatures throughout the
year. Extremes of terrestrial climates are experienced by Macaronis and
Erect-crested penguins, but neither species winters in its breeding area
and neither has found a radical alteration of plumage length necessary.
The conservatism of eudyptids may arise from their use of superciliary
plumes as decoration. Small changes in length of the body plumage,
under a simple genetic control, may necessarily be accompanied by
radical and possibly disgenic changes in length of superciliary plumes.
Penetration of Antarctica has by contrast necessitated considerable
plumage lengthening in Adblies and Southern Gentoos. Future studies
may suggest why a similar change was not found necessary by Chinstraps. In the genus Aptenodytes the short plumage of the King may
represent an ancestral condition (necessitating an inflection in the
regression curve) from which Emperors, like Adblies, have deviated.
It could similarly be argued that variations in flipper area are primarily
determined by condition8 on land, although here the evidence is less
conclusive within genera, and further studies are required. The precise
role of the flipper as a radiator of surplus heat has yet to be defined in
a range of species from warm and cool environments, although the
circumstantial evidence already presented is sufficient to establish a
case for further study.
ACKNOWLEDGMENTS
I thank the Directors of the following museums for allowing me to
examine specimens in their keeping: American Museum of Natural History, British Museum (Nat. Hist.), Museum d’histoire naturelle, West
Australian Museum, Dominion, Canterbury and Okago Museums. This
work was assisted by grants from the Chapman Memorial Fund and the