CONDITIONS IN ENVIRONMENT 283 



multiplication of the Jay or of the Magpie 

 robs us of many a songster. 



By inorganic I refer to the changes in the 

 climate and in the surface of the earth. The 

 nourishment of the young depends upon a 

 regular supply of food, and the supply of food 

 depends upon the climate which alters in 

 diflferent periods ; in one decade the tempera- 

 ture falls below, whilst in another it rises above, 

 the normal, and, as the insect life fluctuates, 

 so there is fluctuation in the bird population. 

 The changes in the surface of the earth are 

 manifold. Little by little the alder {Alnus 

 glutinosa) overspreads the marsh. Young 

 shoots spring up here and there, in a few 

 years grow into bushes, and in a few more 

 years are trees ; and the dense masses of rush 

 which seemed to choke their growth, yielding 

 their position of importance, slowly disappear. 

 And where formerly the Orchis latifolia. Orchis 

 maseula, and Juncus communis grew in mingled 

 confusion, nothing but water, moss, and the 

 spreading roots of alder cover the ground. 

 As the rush disappears, many birds that for 

 generations have inhabited that marsh must 

 seek accommodation elsewhere. Ancient breed- 

 ing haunts thus disappear, new ones come into 

 being, and even those which appear to be 

 permanent are almost imperceptibly changing. 



Now the bird inherits a nervous system, 

 which works under internal excitation and 

 external stimulation. Given the appropriate 

 organic condition and adequate stimulation. 



