ECOLOGICAL FACTORS 389 



sinks to + 11° in Tasmania; a large number of mammals and birds 

 attain a significantly larger size in Tasmania than in Australia: 42 the 

 duckbill is larger than on the mainland, the anteater Echidna is not 

 only larger in Tasmania but also possesses a thicker pelt, the Tas- 

 manian giant kangaroo (Macropus giganteus fuliginosus) somewhat 

 exceeds that of the continent in size and has a coarser fur. The same 

 can be applied quite generally to the birds ; reference may be made to 

 Corvus coronoides,^ and also to the Tasmanian species Gymnorhina 

 organicum, which is larger than the vicarious Australian species 

 G. tibicen. 4 * Corresponding comparisons apply to the north and south 

 island of New Zealand. The north island has an essentially warmer 

 climate, with an average yearly temperature of + 16.6° in Auckland; 

 on the southern island with its mountains rising to an elevation of 

 3000 m. the average yearly temperature is only 10.4°, even at Dunedin 

 on the seacoast; the same or corresponding species are larger on the 

 southern island than on the northern island. The same is true of the 

 modern Apteryx as well as of the extinct Moas, 45 of the parrots of 

 the genus Nestor and of an entire series of other birds.* 



In closing the discussion of the Bergmann principle it is interesting 

 to note another type of exception: while cold Alaska is a center for 

 maximum size of many species of birds and mammals, warm Somali- 

 land is a similar center for minimum size of its homoiothermal animals 

 as compared with the same species in African territory nearer the 

 equator. 



In keeping with this general rule we find that mammals of cold 

 climates have their heat-radiating surfaces decreased by a reduction 

 in size of the ear and tail, by a shortening of the neck and legs, in 

 general by a more compact form. This has been referred to as Allen's 

 Rule. Mammals with such a great surface as the bats are mainly 

 inhabitants of the warm regions. The flying foxes (Megachiroptera) 

 belong entirely to the tropics. Of the 16 families of Microchiroptera, 

 9 are confined entirely to the tropics, 4 are tropical and subtropical in 

 distribution, and only 3 extend into the temperate zones; and even of 

 these the large family of Vespertilionidae has only 10 of its 33 genera 

 in the temperate latitudes. 47 The ears of the hare become shorter 

 towards the north: the African rabbits are slender and have strikingly 

 long ears; in contrast, the Arctic hare of the Old World (Lepvs 

 timidus) has much shorter ears than the field hare {Lepus europaeus) , 

 or the alpine hare (L. varronis) . The same picture presents itself in 



* Representative forms from the genera Glaucopis, Turnagra, Petroeca, Miro, 

 and Sphenocacus.** 



