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- 
9 
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 falling to the ground. 
They leave no offspring to inherit their defects. 
122 
