no ANIMALS OF LAND AND SEA 



The large birds progress ordinarily in a straight line, with a 

 slight raising and lowering of the body at every wing beat if 

 the flight is slow, as in the herons. Their momentum and the 

 kite-like effect of their heavy bodies tend to keep them up, 

 and they are very careful not to lose altitude on account of 

 the great difficulty they experience in rising again. Most of 

 the small birds have a wavy or undulating flight which is 

 especially well seen in the finches and the wood-peckers. The 

 rapidity with which they descend when the wing beats cease 

 shows how slight their momentum is, and how essential for 

 them is the great development of lifting power. 



Very many of the larger broad winged birds, as hawks, eagles, 

 vultures, ravens, pelicans, cranes, spoonbills, screamers, herons, 

 etc., are able to circle on motionless wings, gradually rising 

 higher and higher, until they almost or quite disappear. These 

 birds are large and heavy, and compared with small birds their 

 wing area is relatively less. How do they do it? 



Birds seldom soar in cloudy weather, or in cold regions, 

 or in the winter. Soaring is only possible when the earth is 

 heated by the sun's rays. When the earth is heated the warm 

 air just above it rises, and if the heating is intense and long 

 continued strong columns of air rise for very considerable 

 distances, especially over small hills. In these ascending 

 columns of air the birds find a breeze of considerable strength 

 blowing directly upward the force of the ascending air being 

 sufficient not only to keep them up but to enable them to 

 glide continually downward, yet at the same time rise. 



Birds soar in circles in order to keep within the ascending 

 column of air; if they fall over the edge of the column they 

 begin to flap in order to get back into it again. You some- 

 times see a hawk do this. Soaring is a very popular pastime 

 of the large birds in the drier regions of the tropics, and in 

 some places, as in Egypt, hundreds of birds of many sorts may 

 frequently be seen soaring together. One of the most expert 

 of the soaring birds is the great clumsy looking adjutant of 

 India, which by many is supposed to sleep while soaring. In 



