PROGRESSION IN OR THROUGH THE AIR. 



203 



the one wing as compared with the other ; or to keep the 

 one wing extended while the other is partially flexed. The 

 neck, feet, and tail may or may not contribute to this result. 

 If the bird wishes to rise, it tilts its entire body (the neck 

 and tail participating) in an upward direction (fig. 59, p. 126 ; 

 fig. 102, p. 183); or it rises principally by the action of the 

 wings and by muscular efforts, as happens in the lark. The 

 bird can in this manner likewise retain its position in the 

 air, as may be observed in the hawk when hovering above 

 its prey. If the bird desires to descend, it may reverse 

 the direction of the inclined plane formed by the body and 

 wings, and plunge head foremost with extended pinions 



Fig. 106.— The Pigeon (Treron hicincta, Jerclon>, flying downwards and turning 

 - prior to alighting. The pigeon expands its tail both in ascending and 

 descending.— Ori<7i?mL 



(fig, 106) ; or it may flex the wings, and so accelerate its 

 pace ; or it may raise its wings and drop parachute-fashion 

 (fig. 55, p. 1 12 ; ^, of fig. 82, p. 158) ; or it may even fly 

 in a downward direction — a few sudden strokes, a more 

 or less abrupt curve, and a certain degree of horizontal 

 movement being in either case necessary to break the 



slightly upwards, at the same time raising his left side" and wing, and lowering 

 the right in proportion to the sharpness of the curve he wishes to make, the 

 wings being kept quite rigid the whole time. To such an extent does he do 

 this, that in sweeping round, his wings are often pointed in a direction nearly 

 perpendicular to the sea ; and this position of the wings, more or less inclined 

 to the horizon, is seen always and only when the bird is turning."—'' On some 

 of the Birds inhabiting the Southern Ocean." Ibis, 2d series, vol. i. 1865, 

 p. 227. 



