NESTING ACTIVITIES OF NODDY AND SOOTY TERNS. 79 



chick, based in part upon its appearance, in part upon its "feel" in the nest, 

 its cries, and its reactions to the parent. None of these alone seems sufficient 

 to form the basis of an absolutely positive recognition, and it is probable that 

 the conflicting behavior of the bird is due to the imperfect integration of some 

 such groups of impulses as the following : 



(1) Positive reaction to the appearance of the nest and its contents, and to 

 the nest locality. 



(2) Disturbance of this caused by the changed appearance of the young and 

 leading to greater sensitivity to other stimuli. 



(3) Postive reaction to feel of chick in the nest; this likewise disturbed by 

 the substitution of the larger chick. 



(4) Positive reactions to the cries of the chick. 



(5) Defending reaction to the situation, chick attacked by adult. (For more 

 detailed examples of this see p. 83). 



(6) This defending reaction is established as a habit which temporarily 

 exceeds even (1) in force. 



All these factors are apparent in the activities of this bird and stand out 

 more or less clearly in the reactions of most of the sooties to their own and to 

 other young. Recognition of the young at this stage thus appears to be the 

 result, in part, of the pattern of visual and tactual stimuli offered by the chick ; 

 in part, of the behavior of the chick in the nest region (experiment 16). Com- 

 plete recognition is the result of a complex of many sensory-motor reactions, 

 not merely of a single type of stimulus. 



With older chicks, after the tenth day, it is almost impossible to carry out 

 observations unless full time may be devoted to them. They lie hidden 

 among the bushes during the greater part of the day and come out to their 

 nests only at the return of their parents. They are extremely wild and run to 

 cover whenever the colony is disturbed. They show a familiarity with the 

 nest region almost equal to that of the adult birds, returning readily to the 

 nest alone, threading their way among other nests and avoiding the attacks 

 of strong adults. From such observations as I have been able to make I 

 believe that the chicks usually take the same cover and that both chick and 

 parent become perfectly familiar with the details of the most direct path from 

 this to the nest, meeting one another at various points along the path and 

 reacting to one another, at least in part, by virtue of their presence in this 

 familiar neighborhood. 



Watson has shown that when the appearance of adult birds is completely 

 altered, as by painting their breasts and head with brilliant colors, they are at 

 first rejected by their mates, but this rejection is not permanent and the dis- 

 figured birds are finally accepted by their mates by reason of their persistence 

 in their normal activities in the region of their nests. The "recognition" 

 through the interrelation of habits overcomes the disturbance produced by the 

 changed visual situation. For the recognition of the young, the same complex 

 of reactions must be established. The visual stimulus provided by the young 

 at the nest calls out the normal brooding activities. A slight change in the 

 appearance of the young interrupts the normal series of activities and leads 

 to trial movements. If the situation remains otherwise unchanged if the 

 behavior of the young gives the customary series of stimuli the changed 

 appearance comes to be disregarded. 



