INTRODUCTION. 



There is no need to give any elaborate definition of 

 birds ; they are animals with feathers, the possession 

 of these being a unique distinction. Among other 

 vertebrates the reptiles are the most closely related to 

 them, and, in fact, if birds did not possess feathers, it 

 would be doubtful if they could be separated from the 

 reptilian class. The feathers of birds, it may be noted, 

 do not grow all over the body in most cases, but in 

 definite tracts, differing in the various groups ; these 

 may be well seen in a young Pigeon or Sparrow while 

 fledging. 



In size and form birds do not display the same varia- 

 tion that is found in other vertebrates, such as beasts 

 and fish. 



The largest known bird is the Ostrich, which may 

 stand eight feet high, and the smallest is the Vervain 

 Humming-bird (MelUsitga minima), which is about the 

 size of a large humble-bee. 



There is no evidence from geology that any flying 

 bird ever existed at all approaching the size even of 

 the Rhea, and as large birds commonly have a diffi- 

 culty in rising on the wing, it may be that flight, for 

 birds over a certain size, becomes impossible. The 

 heaviest known flying-bird appears to be the Great 

 South African Bustard {Eupodotis kori), which may 

 attain a weight of over fifty pounds, but its span of 

 wing is little more than eight feet, whereas the largest 

 Albatross may attain to a yard more than this. 



