184 TEXT-BOOK OF ZOOLOGY 



■which, in turn, require the presence of a large sternum with prominent 

 keel. 



(b) The forked tail forms an excellent rudder. The slightest move- 

 ment of one of the long lateral rectrices alters the direction of the flight. 



(c) The neck being short, the head and body form a pointed wedge, 

 which cleaves the air with ease (compare with seal, otter, fishes, etc.). 



(d) The plumage is smooth and in close contact with the body 

 (diminishing friction). The upper side is of a glossy blue-black; 

 forehead and throat chestnut brown ; under-side rufous-yellow ; each of 

 the five outermost tail-feathers has a white spot. 



(e) On account of the legs being short and weak, the weight of the 

 body is considerably reduced. In consequence of its weak feet, the bird 

 is not adapted for walking or hopping, but is capable of perching, and by 

 reason of its sharp claws well fitted for clinging (in nest-building). The 

 swallow, in fact, is as exclusively adapted to an aerial as, say, the 

 ostrich to a terrestrial mode of life. 



3. Being endowed with acute sight, the swallow can spy out the small 

 insects which form its food even from a distance. One sudden turn, and 

 the prey has vanished, as though it had been caught in a butterfly-net, 

 in — 



4. The wide mouth, the gape of which extends back towards the eyes. 

 The beak alone is too small to be of any use for the capture of insects. 



5. The bird can dispense with a long neck (see bat), since it seizes its 

 food on the wing, and can turn with playful ease in every direction. 



6. The nature of its food necessitates the departure of the bird in 

 autumn to the South. At the end of September or the beginning of 

 October, when the second brood is fledged and fit for travel, the birds 

 assemble on the church steeples, roofs, etc., and perform a number of 

 preliminary trials in flying. At last, on some fine evening soon after 

 sunset, the feathered host rises for the last time, and commences its 

 journey to the warm and insect-abounding shores of Africa. 



Allied Species. 



The House-Martin (Chelidon urbica), like the swallow, cultivates the 

 companionship of man. It builds its nest mostly on the outside of 

 houses, under projecting roofs and window-sills, in recesses, etc. (as a 

 protection from rain. The nest is hemispherical, the opening being just 

 large enough to allow the bird to slip through (protection against 

 plunderers). If the opening happens to be too large, some vagabond 

 sparrow is only too likely to take unlawful possession of the dwelling. 

 The plumage of this confiding bird is glossy black above and white on 



