forward on a rapidly descending curve in the interval between 

 the wing-beats. This gives rise to what is known as an 

 " undidating " flight. But the large passerines, Uke the 

 crows, differ conspicuously in their method of progress. With 

 them the wing beats relatively slowly, so that its shape can 

 be readily seen ; and their course is direct — Whence the familiar 

 saying " straight as the crow flies." Further, the inner 

 webs of the outer primary quills are, what is called " emar- 

 ginate," that is to say, the width of the web is suddenly 

 reduced towards the tip of the feather, so that the out- 

 stretched wing has a conspicuously frihged appearance, as 

 may be seen at a glance at the beautiful pen-and-ink sketches 

 on another page. The eagles and falcons have similar 

 emarginations. 



But to return for a moment to the smaller passerines. 

 There are very few of our native species which could be dis- 

 tinguished in the field by their flight alone. For the most 

 part one has to rely on this and clues afforded by character- 

 istic markings : while a further aid is afforded by at least a 

 slight knowledge of the haunts of birds. One would not 

 expect to find a wheatear in a wood, or a wren in a reed-bed. 



The wagtails are among the easiest of the " undulating " 

 fliers to distinguish, if only because of the great length of the 

 tail. The pied-wagtail, with its black and white plumage — or 

 black, grey, and white in the winter — can be identified at a 



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