38 BIRDS OF THE JAPANESE EMPIRE. 



Japanese Islands bear almost exactly the same relation to the east 

 coast of the Pal^arctic Region as the British Islands do to its west 

 coast. The Paljearctic Eegion, as defined by Sclater and Wallace, 

 is a very clearly defined one so far as the majority of birds are con- 

 cerned. The range of many species of birds extends uninterruptedly 

 from the British Islands across Europe and Siberia to Japan. Of 

 course there is no species of bird which is found both in Britain and 

 Japan but not in the intervening district. Cases of interrupted 

 areas of distribution are almost unknown, though, as will hereafter 

 appear, there are many cases in which West-European birds re- 

 semble more closely East- Asiatic ones, than the Siberian races which 

 intervene. This is unquestionably the most remarkable fact con- 

 nected with the birds of Japan, and it is one which has not been 

 insisted upon as much as it ought to have been. 



It is an undoubted fact that in most species where climatic variations 

 of colour occur, the extreme of whiteness is not found in the examples 

 from Central Siberia, but in those from Kamtschatka. The mean 

 annual temperature of the former locality is nearly twenty degrees 

 lower than that of the latter, and the mean winter temperature shows 

 a much greater difference. Nearly all the species which appear to 

 exhibit these climatic variations of colour are resident birds, which 

 moult only once a year, in July and August ; and the mean tempera- 

 ture of July, when the new feathers are forming, appears to coincide 

 with the variation of colour so closely that it is difficult to resist the 

 conclusion that they are cause and effect. 



The Common Nuthatch {Sitta casia) ranges completely across 

 Europe and Siberia from the British Islands to Japan. Throughout 

 this extensive range very little variation occurs in the colour of its 

 upper parts, which is a bright slate-grey. On the other hand, the 

 variation in the colour of the underparts is very remarkable. In the 

 West the range of this species extends as far south as Algeria, where 

 the colour of the underparts is dark bufi", paler on the throat. Pro- 

 ceeding in a north-easterly direction, little change is observable until 

 the Baltic is reached, when the white on the throat gradually increases, 

 until at Dantzig it has covered the breast, and at St. Petersburg it 

 has spread over the belly. In Central Siberia the underparts, except 

 the extreme flanks and the under tail-coverts, are snow-white, but in 

 the valley of the Amoor and in Southern Japan the bufi" has reap- 

 peared on the belly, and the Dantzig bird is reproduced. The 

 southern limit of the eastern range of this species appears to be South 



