12 BIRDS OF THE WORLD 



process known as selection. That is to say, birds 

 which, by some peculiarity in their structure, found 

 themselves able to capture and thrive upon the flesh 

 of other animals, including other birds, went on com- 

 peting among themselves for this particular kind of 

 food, and those which were best endowed — that is to 

 say, those which by their longer wings or sharper beak 

 and claws, or by their ability to swim and to dive — 

 gradually crowded out their less fortunate fellows. 

 As time passed, the peculiar characters and qualities, 

 which originally gained for them superiority over their 

 neighbours went on increasing, because the competi- 

 tion continued, being rendered, indeed, the more 

 severe because carried on between fewer rivals — ^but 

 rivals almost equally well fitted for the struggle. And 

 thus, in course of time, by slow degrees, the various 

 forms of birds have come to be. To-day, as a result, 

 we find such differing types as Diving-birds and Tree- 

 climbers, Hawks and long-legged Waders, and so on. 



These different kinds of birds we group together 

 in assemblages which are known as "Orders," and 

 these are further sub-divided into Sub-orders, 

 Families, and Genera, until finally we come to the 

 division into species. In this way we can sort out and 

 bracket together all kinds of birds according to their 

 relationship one to another. 



While some Orders are made up of birds which 

 have retained a relatively large number of characters 

 that are certainly survivals of very ancient times, and 

 are hence said to be primitive, others have undergone 

 great changes in structure and show many signs of 

 descent from the less modified, less changed forms, and 



