Mat 29, 1908] 



SCIENCE 



849 



experience and the power to learn. In 

 altrieious birds imitation is not very effect- 

 ive before the young leave the nest, but is 

 more marked in precocious birds at an 

 early period. Imitation is most striking 

 in fully grown but immature young, as in 

 bluebirds, which still follow their parents, 

 but are not wholly dependent upon them, 

 or in gull chicks, which are fed by regurgi- 

 tation, and often have to wait a long time 

 before the food is produced. 



Does the adult bird show intelligence in 

 serving the proper quantity of food, and 

 in distributing it to the young? The an- 

 swer is no ! What the old bird really does 

 in effect is to "test" the reaction of the 

 throat of each nestling, and await the re- 

 sponse. If a bird does not respond quickly 

 the food is withdrawn and another is test- 

 ed. Thus is the food always passed around 

 until a bird with the proper reaction time 

 is found. There is no evidence that such 

 "tests" are deliberately or consciously 

 made. The amount of food taken by the 

 young is determined reflexly by the gullet, 

 which acts as a brake upon the tendency 

 of the young to gorge itself to suffocation. 

 The bird with full gullet can not as a rule 

 respond, and must wait. 



Does the old bird display intelligence in 

 the kind of food served, or in the treatment 

 which it receives? It probably does. 

 While a good deal of instinct is involved 

 in all these matters, the parent does not act 

 like a machine, but the young are provided 

 with food adapted to their growing needs. 

 A gull chick, one half hour old, gets small 

 pieces of predigested fish, while at three 

 weeks of age it may be invited to bolt an 

 entire squid. 



What can be said of the general intelli- 

 gence displayed by old birds? We find 

 that their various instincts become modified 

 or refined by habit or association at almost 

 every step. Thus behavior becomes ever 

 more definite, and their life tends to run 



in grooves. They quickly form the habit 

 of going to their nesting site by a definite 

 path. If the branch which holds the nest 

 is cut off and removed but a few feet away, 

 the old bird wiU try to follow her usual 

 course and hover at the point in space 

 formerly occupied by the nest, even when 

 in sight of her young, and will repeat these 

 actions many times before actually going 

 to the nest. But this behavior abruptly 

 ends when the new site of the nest is once 

 visited. After the nest is built, or even 

 while construction is in progress, a definite 

 habit of approach is formed, which may 

 involve walking along a certain limb or 

 grasping certain twigs. The habit of en- 

 tering the nest from a certain side, facing 

 the same way while sitting on the eggs, 

 grasping the same branch when inspecting 

 or cleaning the nest, and leaving the nest 

 in a definite manner, are all more or less 

 stereotyped and fixed by habit in a rela- 

 tively brief course of time. 



Do birds discriminate their own eggs and 

 proper young? Very many do not, but 

 some do, sooner or later. The success of 

 the European cuckoo, or the American cow- 

 bird, whose young are reared by foster 

 parents of many species, would argue for 

 little power in this direction. Yet, in some 

 cases, the foreign body is removed, or the 

 nest is deserted through fear. 



In the cyclical instincts of the repro- 

 ductive period intelligence in the wild bird 

 is mainly displayed by the formation of 

 habits through association. In the same 

 way drinking and bathing places, perches, 

 spots for dusting, for sun-bathing and 

 sleeping are resorted to by habit, for longer 

 or shorter periods, according to the other 

 conditions which modify behavior. 



How does the wild bird meet emergen- 

 cies? Do their acts ever suggest abstract 

 thought, deliberation and planning, and do 

 they generally offer any effective aid to 

 companions in distress? Such important 



