SONG-BIRDS 183 



and give increased firmness to the structure, which is left open above. 

 (Chopped straw is mixed with the mud used in some districts for 

 building walls and even entire houses.) When dry, the nest is lined 

 with a soft and warm padding of straw and feathers. After about two 

 weeks' careful incubation the young emerge from the egg, and are fed 

 and tended by the old birds with the utmost solicitude. As the nest is 

 established in buildings, the young are protected against wet and cold, 

 and being, moreover, placed close under the roof, the young birds 

 are safe from the attack of mice, weasels, or polecats. From birds 

 of prey the swallow is protected by its enormously rapid flight; the 

 hobby alone is able to overtake it. 



C. The Swallow as a Pursuer of Insects. 



The food of the swallow consists of all sorts of small insects, 

 especially flies and gnats, which it pursues in their own domain, 

 the air. 



1. Small creatures like this, however, provide but scanty fare, con- 

 sisting as they do chiefly of such indigestible material as body-armour 

 and wings. Hence only small animals can support themselves on prey 

 of this description (compare with mole). 



2. To satisfy its needs, the swallow requires large quantities of these 

 animals, particularly since they are sparsely scattered over a vast 

 space, and the fatiguing motion of the wings entails a great expenditure 

 of force (compare with bat). Being, however, an extremely nimble and 

 rapid flier, and able to accomplish astonishing distances day by day, the 

 swallow manages to get sufficient food to satisfy its wants. In dull, 

 rainy weather it flies close to the surface of the ground, where insects 

 are to be found under these conditions. Flies or gnats sitting on walls 

 it tries to rouse by rushing past them, in order to seize them on the 

 wing. In warm sunshine, however, it rises high up in the air, still in 

 pursuit of insects (consequently it is regarded as a weather-prophet). 

 Seemingly at play, the bird performs all kinds of gambols in the air, 

 now shooting forward headlong with the speed of an arrow, by turns 

 ascending and descending, executing the boldest sideward movements, 

 suddenly veering round and again darting forward on its former course. 

 Now it seems to be dashing forward headlong against a wall ; now, again 

 diving downwards, we expect to see it disappear beneath the water. On 

 the wing it drinks, on the wing it takes its cooling bath. In fact, the 

 bird presents a picture of incessant life and motion. How is it able to 

 perform all these astonishing manoeuvres ? 



(a) The wings are long, narrow and pointed (compare, on the other 

 hand, the fowl). They are set in action by powerful thoracic muscles, 



