GHAP. II THE ELEMENTARY FACTS OF DISTRIBUTION 23 



will be much affected ; and these are what we have chiefly 

 to consider as bearing on the questions here discussed. 



The first thing that strikes us on looking at the map, is, 

 the small amount of overlapping of the several areas, and 

 the isolation of many of the species ; while the next most 

 striking feature is the manner in which the Asiatic species 

 almost surround a vast area in which no jays are found. 

 The only species with large areas, are the European G, 

 glandarius and the Asiatic G, Brandti. The former has 

 three species overlapping it — in Algeria, in South-eastern 

 and North-eastern Europe respectively. The Syrian jay 

 (No. 4), is not known to occur anywhere with the black- 

 headed jay (No. 3), and perhaps the two areas do not meet. 

 The Persian jay (No 5), is quite isolated. The Himalayan 

 and Chinese jays (Nos. 7, 8, and 9) form a group which 

 are isolated from the rest of the genus ; while the 

 Japanese jay (No. 11), is also completely isolated as 

 regards the European jays to which it is nearly allied. 

 These peculiarities of distribution are no doubt in part 

 dependent on the habits of the jays, which live only in 

 well-wooded districts, among deciduous trees, and are 

 essentially non-migratory in their habits, though 

 sometimes moving southwards in winter. This will 

 explain their absence from the vast desert area of Central 

 Asia, but it will not account for the gap between the 

 North and South Chinese species, nor for the absence of 

 jays from the wooded hills of Turkestan, where Mr. N. A. 

 Severtzoff collected assiduously, obtaining 384 species of 

 birds but no jay. These peculiarities, and the fact that 

 jays are never very abundant anywhere, seem to indicate 

 that the genus is now a decaying one, and that it has at no 

 very distant epoch occupied a larger and more continuous 

 area, such as that of the genus Parus at the present 

 day. 



Discontinuous generic Areas. — It is not very easy to 

 find good examples of genera whose species occupy two or 

 more quite disconnected areas, for though such cases may 

 not be rare, we are seldom in a position to mark out the 

 limits of the several species with sufficient accuracy. The 

 best and most remarkable case among European birds is 



