then, is another instance of what can be learned of the past history 

 of a bird by a careful scrutiny of the nestling. Sometimes we shall 

 find our evidence in the wing, sometimes in some other organ 

 The sequence of plumage affords abundant evidence of this. But 

 that is another story. 



So much for the " intensive " study of the wing. A brief 

 reference must now be made to the constantly repeated state- 

 ment that nestling birds are " taught " to fly by their parents. 

 There is no evidence whatever to support this belief : and much 

 that goes to show its improbability. 



Failing more suitable sites, sand-martins will often elect to 

 build their nests in the crevices of the masonry of bridges. 



From the mouth of this substitute for a burrow is often a 

 sheer drop of many feet to the stream below. When the nestlings, 

 fully fledged, leave their nursery for the first time they must 

 either " fly " from the moment they take the first plunge from the 

 masonry, or die. Failing to make the appropriate movements 

 of the wings nothing can save them from a watery grave. There 

 can be no " teaching " to fly. Indeed, death no less certainly 

 awaits every house-martin when it plunges into space from the 

 edge of the nest. The appropriate wing-movements, necessary 

 to produce flight, in short, are " instinctive." Those with 

 defective instincts are forthwith killed by falHng to the ground. 

 They leave no offspring to inherit their defects. 



122 



