338 THE BIOLOGY OF BIRDS 



§ 5. Instinctive Behaviour 



When a nestling opens its mouth at the touch of food 

 in its mother's bill, that is a reflex action. When rooks 

 break the shells of river-mussels by letting them fall from 

 a height, that is probably intelligent behaviour, involving 

 some sort of perceptual inference. Now between these two 

 levels there is an area of activity which we call instinctive. 

 From the physiological side, instinctive behaviour is like a 

 chain of complex reflex actions, each pulling the trigger of 

 its successor ; but it seems to have a psychological side 

 as well, being suffused with some degree of awareness and 

 being backed by conscious endeavour. No learning is 

 necessary, as in the case of intelligent behaviour, but practice 

 may add a touch of perfection. There is often an almost 

 tyrannical compulsion, in which routine-efficiency defeats 

 itself, and yet there are many instances of plasticity where 

 the behaviour is slightly adjusted to novel circumstances. 

 Of birds and mammals it may be said with some proba- 

 bility that some hitch in the instinctive routine is often an 

 opportunity for intelligence to take the reins. But there is 

 no warrant for regarding instinct either as " low-grade 

 intelligence " or as " lapsed intelligence " — it is on a different 

 evolutionary tack. While intelligence is as much made as 

 born (though the general capacity of learning is of course 

 part of the inheritance), instinct is much more inborn than 

 made. 



Illustrations o£ Instinctive Behaviour. — A young coot 

 swims right away when it is tumbled into the water for the 

 first time, and this is true in many cases. The capacity 

 for executing the requisite swimming movements is laid 

 down as part of the constitution, as a pre-established 

 concatenation of certain nerve-cells and certain muscle- 

 cells. But it requires an appropriate stimulation to set it 

 agoing, and this may be supplied by some teaching on the 

 parent's part. Thus in the case of the great crested grebe 

 the mother plays a part in educating the young ones for 



