54 



pheasant weigh ahnost the same, yet the former has an expanse 

 double that of the latter, and a common tern weighing only 4oz. 

 has an expanse about equal to a pheasant. The guillemot has the 

 smallest wings, in comparison to its size, than any other British 

 bird, but its flight is one of the swiftest in a straight steady course 

 by great rapidity of wing strokes. 



Birds have three principal modes of flight — 1, gliding or skim- 

 ming ; 2, sailing or soaring ; 3, active strokes of the wing. 



Glidbui. — When a bird has acquired a certain velocity' it ceases 

 to beat its wings, and with them and the tail extended it glides 

 along in a forward motion either horizontal, ascending or descend- 

 ing. This is a common form of flight with buzzards, gulls and 

 other large birds of ample wing area. See diagram fig. 1, pi. ii. 



A falcon swooping down on its quarry descends w^ith extra- 

 ordinary velocity by means of its wing being only partly expanded 

 (fig. 2), should it miss its mark striking at its prey it is enabled by 

 sudden expansion of its wings and elevating its head to instantlj^ 

 glide upwards, which action is due to the impetus and formation of 

 its wings. Consequently a bird with its wing brought forward 

 (fig. 1) glides slowly, and one with its wings only partly expanded 

 (fig. 2) glides Avith great rapidity. It can alter its course when 

 gliding by slightly turning its head to one side or by partly closing 

 one wing, the bird then turns to the same side. 



Soarinij. — Typical soaring birds are eagles, buzzards, falcons, 

 owls, gulls, and crows. Most soaring species are of large size and 

 possess great Aving area. But it is only w^hen a certain amount of 

 wind prevails that soaring is possible and it is perfected during a 

 strong wind. In a calm it is not possible. Thus in a wind, after 

 an elevated position is attained by w4ng strokes, it can then sustain 

 itself on outstretched wing, and without further apparent motion of 

 its wings describe circles and curves which enables it to glide both 

 up and down the wind. One of the finest examples of such flight 

 is performed by a soaring buzzard, which is also capable of ascend- 

 ing to a very great height by a series of a few wing strokes at 

 regular intervals ; between each series it sails round and round for 

 about three times forming a perfect spiral figure, by this means I 

 have watched them soar upwards until appearing as a tiny black 

 speck in the sky. Gulls may frequently be observed soaring to and 

 fro and up and down in front of a cliff, which they appear to 

 delight in doing when a strong wind is blowing direct against a 

 cliff and is diverted upwards, in this strong current of ascending air 



