The Audubon Societies "^g 



energy. We know that, of all living creatures, birds have the greatest amount 

 of energy and are most tireless in their activities. The secret of this fund of 

 power must be sought in the organs of digestion and circulation. 



One might suppose that a much larger body would be needed to generate as 

 much energy as a bird needs, and that a framework of elephantine size, for 

 example, would be productive of far greater speed in flight and endurance in 

 cold, storms, or continuous exertion. That this is not only not the case, but is 

 quite unnecessary and even impracticable. Nature has demonstrated during 

 untold ages; for we have now at hand so many of her former experiments in 

 various types of flying monsters for comparison, that we can safely be assured 

 that the modern bird, endowed with flight, has been developed along the most 

 effective and economical lines, to take its part in the world-complex of living 

 organisms. 



Just how this has been brought about, the study of comparative anatomy 

 tells us, for without it, some of the peculiarities of the bird's structure would be 

 an insoluble puzzle. In this exercise, therefore, let us search for some of the 

 reasons why a bird is able to produce and keep up so great an amount of motor- 

 power, or energy, observing that this energy is most strikingly expressed in the 

 form of motion and heat in the case of a bird. When one calls to mind a Hum- 

 mingbird, poising on wings which vibrate so rapidly that they cannot be 

 clearly seen, it is certain that there must be a remarkably perfect mechanism 

 for transmitting the energy which sustains such rapid, and long-continued 

 motion. Great wheels chained to roaring waterfalls and belted to smaller 

 wheels, which in turn move giant gangway saws or huge millstones, scarcely 

 produce an amount of power which will cause more rapid motion. 



Again, if one considers a bird like the Penguin, which nests in Antarctic 

 regions, incubating its single egg and rearing its nestling young successfully 

 with no other aid than a particularly warm blanket of fat which keeps in the 

 heat of its body so that it does not succumb to the cold and freeze, it is clear 

 that the energy necessary to keep up and conserve this body heat must be prac- 

 tically never-failing. 



The temperature of our own bodies as ordinarily taken by placing a tem- 

 perature-bulb under the tongue, is normally 98.6° F. On the surface of the 

 skin the temperature varies around 90° F., while inside the body, in the liver, 

 it rises as high as 107° F. 



Birds normally maintain a temperature of over 100° F, in general 10° to 

 1 2° higher than our own, which is an indication of the rapid rate at which they 

 generate heat. It is useful to remember that no other living organisms have so 

 high a body- temperature. Now the question arises: What produces this 

 wonderful amount of motion and heat, and having once produced it, what keeps 

 it up? A fire will burn fiercely when first kindled, but it soon dies down unless 

 replenished. In a similar manner, as fuel must be constantly supplied to keep 

 up a fire, so fuel in the form of food must be supplied to keep up the energy 



