388 LAND ANIMALS 



averages as follows: those of Florida, 30.8; of North Carolina, 31.8; 

 of Virginia, 33.4; of Maryland, 34.1; of Pennsylvania, 34.9; of New 

 York, 35.3; and of Connecticut, 35.5. 37 The Virginia deer (Odocoileus) 

 of North America becomes progressively smaller towards the south; 

 a dwarf form (0. mexicanus) is found in South America. 38 



Exceptions to the principle of Bergmann are encountered, but 

 when one recalls the many other means at hand for reducing the 

 radiation of heat and the many other factors that serve to regulate 

 body size, the small number of such exceptions is astonishing. Rein- 

 deer afford a mammalian exception; the woodland caribou of North 

 America is larger than its relative of the Barren grounds and the 

 Spitzbergen reindeer is smaller than that of Lapland. 39 There are 

 exceptions among the birds, especially among migrants, which are not 

 exposed to the winter cold in their breeding habitat. An exception is 

 also found in the capercaillie {Tetrao urogallus) , which is smaller in 

 Siberia than in Germany. Among the South American rheas, the south- 

 ern form, Pterocnemia pennata, is smaller than the northern Rhea 

 americana. Among the mammals the burrowing animals may form ex- 

 ceptions, since they, like the migratory birds, can withdraw from the 

 winter cold. For example, Microtus pennsylvanicus is larger in Pennsyl- 

 vania than in Labrador. The raccoons decrease in size northward. Allen 

 claims that the decrease in size corresponds with the transition into 

 the less suitable climate. The hot climate of the tropics is certainly the 

 normal one for kingfishers and orioles, and in spite of this the Berg- 

 mann principle can be applied to them, since they acquire a larger 

 size in the cooler region: the wing length of Alcedo athis bengalensis 

 of India, the Malayan Peninsula, and the Sunda Islands is 68-70-71 

 mm., of A. a. pallida of northern Africa and Palestine 74-75 mm., of 

 A. a. corsicana 75-77 mm., and of A. a.-ispida of Germany, 77-79-81 

 mm.; and similarly Oriolus oriolus kundoo from India, Kashmir, and 

 Afghanistan has a wing length of only 140-142 mm. as compared with 

 149-158 mm. of 0. o. oriolus in Europe. 40 



Laboratory experiments yield similar results. White mice became 

 larger than the stock animals when reared in a temperature of about 

 6.1°C, and smaller when reared at a temperature of 26.3°C, along 

 with other changes. 41 A direct effect, therefore, seems to be involved. 



It naturally follows from the Bergmann principle that in neighbor- 

 ing regions with distinct climatic differences and with related animal 

 population, the differences in size become noticeable simultaneously in 

 many homoiothermal animals. Thus, the faunae of southeast Australia 

 and Tasmania show great similarity in composition; but the mean 

 temperature, which amounts to + 16° on the south coast of Australia, 



