DISPERSAL AND MIGRATIONS 155 



forms, becoming the most pronounced in the 

 latter country. In Japan the humidity returns, 

 and much the same conditions prevail as in the 

 extreme west ; whilst in the dry, sandy districts 

 of the south, pale desert forms are found ; and 

 in the extreme south the climate is suitable to 

 the production of semi-tropical forms, where 

 the colours reach their greatest intensity. The 

 rainfall of a district is also stamped upon the 

 plumage of birds, as is remarkably apparent, 

 for instance, in examples of the same species 

 from the wet or the dry districts of India 

 respectively. This peculiarity may even be 

 observed on a small scale in the British Islands, 

 birds from the wettest districts generally being 

 perceptibly darker in tint than those from 

 localities where the rainfall is not so excessive. 

 Birds from tropical regions where the maxi- 

 mum of humidity and warmth prevails have 

 the greatest intensity of colour, browns and 

 greys being perhaps the most susceptible. Olive 

 browns are characteristic of a medium rainfall; 

 rufous browns unfailingly reflect an excess of 

 moisture. Dry, cold climates bleach ; hot and 

 dry climates have a tendency to produce pale- 

 ness, becoming most pronounced in deserts. 

 We may also remark that some species are 



