NATURAL HISTORY IN ICELAND — ^HUXLEY 



329 



tall trees to nest in, and (we may presume at least partly for that 

 reason) does not exist so far north in Scandinavia as the redwing. 



Then, with such a favorite as the meadow pipit to parasitize, it is 

 at first sight puzzling that there are no cuckoos. It seems probable 

 that the reason is the low density of pipit population. A cuckoo 

 has to keep about a dozen fosterers' nests under observation if it is 

 to succeed in its parasitism, and this would be impossible in Iceland. 



The absence of the rock dove seems also surprising — until one 

 remembers that the species seems to be dependent on weed seeds and 

 other byproducts of human cultivation. 



FiGUKE 1. — Main zoogeographical regions characterizing the distribution of the 

 land animals of the world. The Holarctic is normally divided into two sub- 

 regions, the Palearctic (Old Woi'ld) and the Nearctic (New World). In 

 addition, there are separate ocean regions characterizing the distribution of 

 marine forms, including sea birds; of thes eonly the Atlantic region con- 

 cerns us. 



But I do find it puzzling that the ring ouzel, which likes rocky 

 slopes and in Norway breeds as far north as the North Cape, has 

 not established itself; and still more so that the dipper is absent, when 

 its smaller relative, the wren, has been breeding in Iceland so long 

 that it has evolved into a distinctive subspecies. Of course the 

 streams by which the dipper lives would be frozen over in winter; 

 but some of the dipper population of northern continental Europe 

 migrates southward in winter, and the same might readily have oc- 

 curred in Iceland, while the rest might have done what all the Iceland 



