6 BIRDS IN LONDON 



other species previously unknown in London, 

 and their increase and diffusion. Considering 

 these two facts, one is inclined to say off-hand 

 that the diminution or dying out of one set of 

 species is simply due to the fact that they are 

 incapable of thriving in the conditions in^which 

 they are placed ; that the London smoke is fatal 

 in the long run to some of the more delicate 

 birds, as it undoubtedly is to the rose and 

 other plants that require pure air and plenty 

 of sunshine ; and that, on the other hand, 

 the new colonists* that are increasing are species 

 of a coarser fibre, greater vitality, and able, like 

 the plane-tree in the plant world, to thrive in 

 such conditions. It is really not so : the tits 

 and finches, the robin, wren, hedge-sparrow, 

 pied wagtail, some of the warblers, and the 

 missel-thrush, are as vigorous and well able to 

 live in London as the wood-pigeon. They are, 

 moreover, very much more prolific than the 

 pigeon, and find their food with greater ease. 

 Yet we see that these lively, active species are 

 dying out, while the slow, heavy dove, which 

 must eat largely to live, and lays but two eggs 

 on a frail platform of sticks for nest, is rapidly 

 increasing. 



