42 The Fliyhl and Anatomy of Birds. 



sight; they will swoop with immense rapidity and certainty from 

 very great heii,dits upon small objects close to the ground. Most 

 of the eagles will feed readily on lish, and are gifted with such 

 clearness of sight, that from a great height in the air they can 

 distinguish fish swimming near ths surface of the water, and dart- 

 ing down can seize and carry them off almost unerringly. In the 

 vulture tribe the senses of sight and smell seem to rival each other 

 in excellence, and many anecdotes are told respecting the power 

 of each. 



[The author here furnished one or two anecdotes respecting 

 the marvellous keen-sightedness of vultures, and then continued as 

 follows: — ] 



Another instance of keenness of sight is seen in carrier pigeons, 

 which when they are first let loose wheel round and round in 

 increasing circles rising gradually higher every time. This con- 

 tinues as long as the eye can discern the birds, and hence we 

 conclude that it is also continued after we lose sight of them, a 

 constantly increasing circle being made, till they ascertain some 

 known object enabling them to shape a direct course. It is very 

 interesting to compare the proceedings just described with those 

 of a pigeon let off from a balloon above the clouds. Instead of 

 rising upwards like the former, it descends in gradually increasing 

 circles till it can recognise some indications of the earth below, 

 and discover some object previously known by which to direct its 

 flight. 



There is one more tribe of birds which must be mentioned 

 whilst we are on the subject of sight, viz., that of the owls. Their 

 eyes are larger in proportion and more prominent than those of 

 any other bird, and possess the faculty of being able to see clearly 

 in the darkest night, whilst on the other hand the brightness of the 

 sun bewilders and nearly blinds them. Audubon says of the barred 

 owl — " Its power of sight during the day seems to be rather of an 

 equivocal character, as I once saw one alight on the back of a cow, 

 which it left so suddenly afterwards, when the cow moved, as to 

 prove to me thai it had mistaken the object on which it had perched 

 for something else." 



Let us now turn to the wings and flight of birds : — The wing 

 consists of five principal joints, with a few other small auxiliary 

 ones. 



The bones of the wings are composed of layers of a thin white 

 substance, and in adult birds are almost always hollow; their 

 cavities are not filled with marrow, as those of animals, but with 

 air, which makes them exceedingly light; they have also free 



