78 Habit and Instinct. 



that the exquisitely nice adjustments necessary for all the 

 varieties of bird-flight are purely instinctive. In their 

 finished form they are the result of practice and individual 

 acquisition, but they are unquestionably founded on a 

 congenital basis. 



"As soon as he has the use of his wings," says Mr. 

 Headley,* " a young gull may be seen for a good part of 

 the day busily practising. And the great proficients in 

 the art eagles, vultures, storks, and albatrosses have 

 acquired their skill by experimenting on all varieties of 

 currents." I have no doubt that Mr. Headley is right. 

 One has only to watch with care the flight of birds to see 

 how easily, and with what nicety and accuracy, they feel 

 the wind and adapt their wing-spread to its force and 

 direction. A hawk or a gull may be seen sailing round 

 the coast-line or along a hill-ridge, utilizing the strong 

 upthrow of air which the natural obstacle produces. In a 

 light wind the wings of a tern or a gull are widely spread ; 

 but with a fresher breeze the wing is partially flexed so as 

 to make a more acute angle where the wing bends near 

 the middle of its length. Compare the way in which the 

 sparrow leaps from the ground and whirs off, having no 

 difficulty in rising, with the laboured start of the cormo- 

 rant or the duck, which only by much effort succeeds in 

 rising from the water and getting up speed. The albatross, 

 with all his splendid powers of flight, flaps long over the 

 surface of the sea ere he can rise freely ; and he always 

 starts against the wind. Observe, again, how the lark 

 can rise in a vertical line from the meadow, how well he 

 balances his body, and how skilfully he adjusts his rapid 

 wing-strokes for mounting directly upwards. It cannot 

 be doubted that all this specialized skill in flight is 

 perfected by the individual not without much practice, 



* " The Structure and Life of Birds," p. 232. 



