848 



SCIENCE 



[N. S. Vol. XXVII. No. 700 



and the dangers -whieli surround its home. 

 I shall refer mainly to nesting birds. In 

 all cases the conditions are natural and the 

 behavior free. 



In considering the young we must dis- 

 tinguish between the altricious and pre- 

 cocious species, and remember that between 

 such extremes every shade of difference 

 exists. The cedar waxwing which is born 

 blind and naked may be taken as a type of 

 the altricious group. The moment it 

 bursts its shell, unfolds and dries off, a new 

 class of stimuli assail it. Its sensitive skin, 

 with its tactile organs and ears, begin to 

 register new emotions. Its most striking 

 initial reaction is to rise upon its pot-belly 

 as upon a central pillar or foot, open its 

 wide mouth, and thus display its light- 

 rimmed scarlet "target" of a throat. This 

 reaction might arise from hunger, but it 

 certainly follows mechanically in response 

 to any sound or vibration to the nest. At 

 birth such a nestling is a nearly perfect 

 reaction machine; its responses are auto- 

 matic and reflex, and within the limits of 

 fatigue they are as uniform and continuous 

 as the responses of an electric bell. At this 

 sign from the young the parent goes in 

 quest of prey, discovers and seizes it, ham- 

 mers it to a pulp, it may be, and returns 

 with it to the nest. The nestling repeats 

 the sign, and the food is pressed gently 

 down into its sensitive throat; the swallow- 

 ing reflex is started, and the little bird 

 gets its first meal. Remove this bird from 

 its nest, and this feeding response is given 

 as regularly and as continuously as before. 

 Now approach the same nest upon the sec- 

 ond, or better, upon the third or fourth 

 day and apply the same tests. It will be 

 found that the feeding reaction no longer 

 comes uniformly and invariably, and if the 

 young is again removed from its nest, the 

 response is still more difficult to obtain. 

 The characteristic feeding reaction is now 

 regular and predictable only in the pres- 



ence of the parent, and in its proper en- 

 vironment — the nest. Therefore in forty- 

 eight hours the young cedarbird begins to 

 show the first sign of intelligence by learn- 

 ing to limit its reactions to those which 

 count, or in other words by learning to 

 recognize the coming of the parent. Yet 

 this association, which seems to mark the 

 dawn of avian intelligence, is often far from 

 precise, for when at the age of eight or ten 

 days of age a nestling rises to stretch on the 

 nest its companions will crowd about it and 

 "beg" in the same excited manner, as if it 

 were really the parent just alighted on the 

 nest with food in biU. 



All birds form associations with their 

 nest or the spot on which they are born, 

 and to most it signifies warmth, a place to 

 be fed, and comfort in general. In some 

 cases the young learn to return to the nest, 

 and may go ia and out of it for days or 

 weeks. Altricious birds when once out of 

 the nest seldom return, but this is not due 

 to any lack of association, but to their 

 rising instinct of fear favoring that of 

 flight, or at least the desertion of the nest 

 and possibly their concealment by hiding, 

 when the attunement of these instincts is 

 imperfect. In a few cases the same nest or 

 nest-site may be occupied by the same birds 

 for many successive years. There is no evi- 

 dence that the young of any birds distin- 

 guish their nest as a nest at all, or as any- 

 thing more than a place, as a part of a tree 

 or of the earth. 



The young kingfisher spends four 

 weeks in its underground tunnel, and 

 towards the close of this period, as I have 

 explained elsewhere, it acquires the curious 

 habit of walking backward. In the educa- 

 tion of the young bird it is not necessary 

 to assume that any conscious or deliberate 

 part is ever played by the adults. The 

 phenomena are satisfactorily accounted for 

 by instinct, including imitation on an in- 

 stinctive basis, and association, involving 



