the habit throughout this day for the parents to carry away the 

 excreta. It is well known that many nest-building birds devour 

 the excreta sacs of the young until they reach a certain age (or 

 until a limit is fixed by some other factor) , after which it is car- 

 ried away and deposited. On the occasion of this experiment 

 the male Vireo dropped the green paper to catch the excreta, 

 which he immediately devoured, contrary to the existing habit, 

 and then again picked up the paper and flew away. 



A similar piece of green paper was again placed in the nest, 

 and the female bird came (visit No. 227), and fed a moth to 

 White. Almost exactly the same performance was repeated. 

 One fact of difference being that owing, perhaps, to the earlier 

 stage of development of White, the habit of carrying away the 

 excreta had been more recently established. 



Somewhat later a small bit of paper was rolled into a ball and 

 deposited in the nest, where it remained unseen by the parent 

 birds for several visits. When the female Yireo finally discov- 

 ered it (visit No. 240), she swallowed the excreta sac from White, 

 iustead of carrying it aw^ay, and flew away with the paper ball. 



We cannot suppose that the birds had any knowledge of the 

 nature of the foreign body (the paper), but its presence was a 

 sufficient stimulus, and the removal was the reaction. Some 

 doubt may be expressed as to whether this behavior can be ranked 

 any higher than a reflex act, or an integration of several reflexes. 

 It was here possible for the birds to remove the foreign object. 

 What if it had been too large or too heavy for them to move? 

 Would they not then have been forced to one of the other alter- 

 natives, possibly to abandon the nest or build a superstructure? 

 So that, when the host species does resort to one or other of these 

 two responses in the case of a Cowbird 's egg, is the behavior not 

 explainable in the same terms that we have suggested in the 

 experiment with the paper? 



It would have been interesting could it have been determined 

 in just what manner the paper ball was deposited; since the 

 habit of removing and depositing the excreta sac becomes a more 

 or less stereotyped process in many species. Some birds drop 

 the excreta while in flight, others carefully deposit it on the 

 limb of a tree, or on the ground, etc. The removal of the foreign 

 object (the paper) w^as probably a reaction controlled by very 

 much the same nervous mechanism as that which controlled the 



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