INSTINCT AND INTELLIGENCE IN BIRDS 553 



19, at eleven o'clock, I discovered a black-billed cuckoo in the act of 

 brooding one young bird, a day old, and three eggs, in a small sapling 

 pine, about three feet from the ground. The sitter, thus surprised, 

 quietly retired and sounded her alarm from a distance. Twenty-four 

 hours later, when I visited the scene, and when, as afterwards appeared, 

 a second young bird had emerged, fear was more in abeyance, and the 

 behavior different. I was allowed to approach as close as possible, and 

 stood for twenty minutes, with the eye of the sitter not over twenty 

 inches from my own, and only finally sent her off by trying to take her 

 in the hand. Under these circumstances the cuckoo behaves much like 

 the cedarbird, raising its head, though in a less marked degree, and 

 remaining perfectly quiet, the only motions visible being those of 

 breathing and the momentary flick of the third eyelid or nictitating 

 membrane across the pupil. 



V 



The dawn of avian intelligence in the nestling, if one of the altrices, 

 begins at about the third day, and in relation to the feeding reaction. 

 Resting upon its huge pot-belly, as a central pillar, the little bird raises 

 its trembling head, rather feebly at first, and supporting itself also, it 

 may be, with its wings, and opening its mouth to the widest extent, thus 

 displays its food-target. If the sign is unanswered, the head drops, 

 the mouth closes, vibration ceases, and the bird lies prone, as if ex- 

 hausted, the whole operation, which seems to call into play the entire 

 body, lasting three seconds, more or less, according to the strength of 

 the original stimulus. 



This kind of behavior is a typical illustration of compound reflex 

 action or instinct, and, when feeding follows, the reflexes assume more 

 completely the chain form. "When not due to hunger this response 

 may be evoked at will by any suitable stimulus, whether tactile or 

 auditory, whether the bird is in its nest or out of it, and regardless of 

 the parent. The nestling now reminds one of an electrical toy, the 

 action of which is purely automatic. Place the little bird on a piece 

 of cloth or fold of your clothing and " press the button," that is scratch 

 the cloth with the finger or a lead pencil, and behold this complex feed- 

 ing response. When the nestling has not been fed to repletion, within 

 the limits of fatigue, this reaction may be as automatic, uniform or 

 stereotyped, and therefore predictable, as that of an electric bell. 



Initial responses of this sort are relatively perfect. Consequently 

 they can have nothing to do with past experience. They represent the 

 hereditary powers of a hereditary mechanism. Now the point of 

 greatest interest is that this inherited tendency to respond, in the course 

 of a few days becomes replaced, as it were, by an acquired tendency. 

 Instinct becomes " modified " by association. The mind or intelligence 



VOL. lxxvi. — 38. 



