144 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



have observed of these insects, I am convinced that their warning coloration 

 cannot have reference to either Mantises, Asilidae, or lizards, v^^hich are prac- 

 tically the only other enemies that can be taken into account That 



they [birds] have been the chief, if not the only agents in the production of 

 mimicry whether Batesian or Miillerian I have little doubt. 



In other words selectionists practically rest their case on the re- 

 actions of birds to protective adaptations. The principal object of 

 the present paper has been to show what those reactions are so far as 

 nearctic birds are concerned, and there is no reason to suspect that the 

 results are otherwise than typical for birds of the world. 



The most outstanding feature of the records of the animal food of 

 nearctic birds undoubtedly is the marvellous distribution of them 

 through the phyla, orders, and subordinate systematic groups. Within 

 size limits, animals of practically every kind accessible to birds are 

 preyed upon, and as we consider the records for group after group a 

 tendency for the number of captures to be in proportion to the abun- 

 dance of the animals concerned is unmistakable. Availability un- 

 doubtedly is the chief factor involved in the choice of food, and pre- 

 dation therefore tends to be in proportion to population. 



Considering bird predation alone this principle leads to a high de- 

 gree of indiscriminancy in attack upon the whole kingdom of animal 

 life. The combined attack of birds plus all other predators still more 

 closely approaches complete indiscriminancy. In other words there is 

 utilization of animals of practically every kind for food approximately 

 in proportion to their numbers. This means that predation takes place 

 much the same as if there were no such thing as protective adaptations. 

 And this is only another way of saying that the phenomena classed by 

 theorists as protective adaptations have little or no eflfectiveness. 



Natural Selection theories assume discrimination in the choice of 

 prey. The principle of proportional predation so obvious from the 

 data contained in this paper vitiates those theories for it denotes 

 indiscrimination, the very antithesis of selection. 



Finally so far as the types of adaptations discussed in this paper are 

 concerned the influence of such factors as disease and climatic factors, 

 the last the most important of all in reducing animal populations, is 

 completely indiscriminate. 



The total mortality of animal groups is known normally to be in 

 strict proportion to their numbers, i. c, a pair of the new generation 

 remains, to rei)lace a pair of the old and it is apparent elimination of 

 all but that pair is very largely due to agencies indiscriminate in their 

 action. There would seem, tlicrefore, to be no discriminative eliminat- 

 ing forces of sufficient strength to bear the very great burden put 

 upon them by natural selection theories. 



