. The bird; its form and function . closely watching a swallow as it courses swiftly overa meadow, or shoots upward, buoying itself against thebreeze, we can appreciate the delicate adjustment of themuscles which govern the tail-feathers. Each featherseems vital with life, now sliding one over the other untilall are in a narrow line, then expanding, with less frictionthan ever a fan opened, into a wide-spreading, gentlygraduated fork. The quartet of forked-tailed birds men-tioned above are splendid fliers, but we shall see that skill 4o8 The Bird in flight depends but Httle upon the sh
. The bird; its form and function . closely watching a swallow as it courses swiftly overa meadow, or shoots upward, buoying itself against thebreeze, we can appreciate the delicate adjustment of themuscles which govern the tail-feathers. Each featherseems vital with life, now sliding one over the other untilall are in a narrow line, then expanding, with less frictionthan ever a fan opened, into a wide-spreading, gentlygraduated fork. The quartet of forked-tailed birds men-tioned above are splendid fliers, but we shall see that skill 4o8 The Bird in flight depends but Httle upon the shape of the tip,when we consider certain birds with cuneate tails, orthose in which the central feathers, soft and not rigid,are elongated, instead of the outer ones. The Undulated Grass Parrakeet shows a conditionalmost the opposite of the swallow. The Mexican long-tailed jays, the magjjies, and the tropic-birds are alsoall of this type, the latter being especially fine fliers andcapable of remarkable aerial evolutions. Again, some. Fig. 323.—Tail of Grass Parrakeet. of the flycatchers with moderate, rounded tails can exe-cute most wonderful flight movements, steering in erraticdarts through the air, or darting aside at right angleswhile at full speed, this being accomplished principallyby means of the tail. A tail serves also an important use as a brake. Whena great pelican settles gradually toward the surface ofthe water, or a duck momentarily hovers before alighting,the tail, wide-spread and brought downward, gives effi-cient aid in retarding the impetus. Tails 409 We notice that birds which have very short tails areunable to turn quickly and that their flight is very direct,or even where there is a long tail, if it is principally forornament and not well muscled, it is of little use in help-ing its owner to change the direction of flight. Thepartridge-like tinamous of South America are good exam-ples of the first-mentioned group. Their tails are smalland useless, and when
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbirds, bookyear1906
