62 Bird -Lore 



Of all creatures in our world, birds, we learn, expend the most energy in 

 living and moving. In all prohaliility their blood circulates the most rapidly, 

 their food-capacity is the greatest, and their digestion the fastest of any verte- 

 brate. Why this is so we will try to learn this year in a series of exercises deal- 

 ing with the structure and adaptations of birds. 



I. The Plan of a Bird 



A bird is a vertebrate, that is, it has a backbone protecting a tubular 

 nerve-cord; a blood-system which is closed inside its body in a complex net- 

 work of arteries and veins and capillaries; a skin which we may think of as 

 double, because it is made up of two layers; and limbs or appendages that 

 never exceed four in number. There are more reasons than these that make 

 a bird a vetebrate, but the four mentioned are sufficient for us to remember now. 

 A bird, as a bird, is known by its covering of feathers. No other creature 

 has feathers, but every bird that has ever been discovered bears this dis- 

 tinguishing mark. It is true that a bird is superior in flight to other flying 

 creatures, but it would not be correct to describe a bird by merely saying 

 it could fly. 



The plan of a bird in general is a vetebrate plan, distinguished by the 

 peculiar growth of feathers, and modified in particular for the purpose of flight. 

 Compared with aeroplanes and airships of whatever description, a bird is the 

 most successful, the most highly perfected flying-machine ever devised. It is 

 from this point of view, perhaps, that we can gain the best idea of the struc- 

 ture of birds for the present. In New Years to come, some of you may be in 

 colleges or universities, where you will discover more in detail the astonishing 

 mechanism of a bird, but this year we can only make a beginning in a very 

 simple study of structure and adaptation. 



In addition to adequate motive power, a flying-machine must have three 

 things in order to be air-worthy, namely lightness, rigidity, and equilibrium. 

 It has taken man a long time to invent a machine of this kind, and had 

 it not been for the model of the bird's skeleton and plumage, from which 

 so much has been learned about the mechanism of flight, it is doubtful 

 whether there would be any flying-machines to-day better than Darius 

 Green's. 



The first thing we notice about a flying bird, is its great extent of wing- 

 surface. The better flier a bird is, the longer wings and better muscles of 

 flight it has. If we think of the wings as sails fastened to a bon\' mast (the 

 breastbone) in order that they may be rigid, it may help us to understand why 

 the fore-limbs of a bird are so different from its hind-limbs. 



The best way to get an idea of this difference is to look at the wing-bones 

 and leg-bones of the next chicken or turkey you eat, and notice how dissimi- 

 lar they are. You might examine the wing-bones of very many different 



