74 BIRDS OF LA PLATA 



mind they appear like the merest dust in the balance^ 

 which is not regarded. And how tremendous and 

 pitiless is that searching law of the survival of the 

 fittest in its operations, when we see a species like 

 this Synallaxis, in the fashioning and perfecting of 

 which Nature seems to have exhausted all her art, so 

 exquisitely is it adapted in its structure, coloration, 

 and habits to the one great object of concealment, 

 yet apparently doomed to destruction through this 

 one petty oversight — ^the irrepressible garrulity of 

 the fledglings in their nest ! It is, however, no over- 

 sight at all ; since the law of natural selection is not 

 prophetic in its action, and only preserves such 

 variations as are beneficial in existing circumstances, 

 without anticipating changes in the conditions. The 

 settlement of the country has, no doubt, caused a 

 great increase of Chimangos, and in some indirect 

 way probably has served to quicken their intelligence j 

 thus a change in the conditions which have moulded 

 this Synallaxis brings a danger to it from an un- 

 expected quarter. The situation of the nest exposes 

 it, one would imagine, to attacks from snakes and 

 small mammals, from birdrkilling spiders, beetles 

 and crickets, yet these subtle ground foes have 

 missed it, while the baby-laughter of the little ones 

 in their cradle has called down an unlooked-for 

 destroyer from above. It might be answered that 

 this must be a very numerous species, otherwise 

 the Chimango could not have acquired the habit 

 of finding the nests ; that when they become rarer 

 the pursuit will be given over, after which the balance 



