6o Bird - Lore 



necessary to maintain the heat of the body of any of its activities such as 

 motion, locomotion, or, in man, an activity like the power of thinking. 



Food, then, is the real source of the bird's unsurpassed energy, and, con- 

 sequently, the food-habits of birds form one of the most important and in- 

 structive chapters in their life-history. In this exercise there is not space to 

 devote to the kinds of food birds eat, since our object now is to gain some idea 

 of how food is transmitted into a sufficient amount of energy to maintain the 

 tireless activities of birds. It is evident that whatever the process of taking 

 in and digesting food is, it must be governed by certain regulations. 



Some of these regulations in the case of birds are: 



1. Capacity for a rapid, large, and frequent intake of food. 



2. Capacity for rapid and thorough digestion. 



3. Capacity for rapid elimination of all waste material. 



All of the powerful apparatus necessary to keep up the bird's food-factory 

 must, moreover, conform to the requirements of its general structure, which, 

 we have recalled, are lightness, compactness, and stability. In other words, 

 the bird must at one and the same time keep up a maximum of food-producing 

 energy with a minimum of apparatus. It is a wonderful problem worked out 

 in some of Nature's most perfect ways. 



Watching a bird eat, perhaps the most surprising thing is the amount it 

 eats and the rapidity with which it eats. Although a bird may occasionally 

 get choked or have a pain from such hasty and unlimited eating, it is prob- 

 able that its digestion is so carefully regulated that few upsets of this kind occur. 

 Nature has provided birds with two very effective contrivances to take care of 

 the large amounts of quickly gulped food, namely a crop and a gizzard. The 

 crop, you may recall, is between the mouth and the stomach, a sort of half-way 

 reservoir where food can be stored until the stomach is ready to take charge of 

 it. Now a bird's stomach is made up of two parts, a proventriculus or glandular 

 stomach, resembling the human stomach, with gastric juices to aid in breaking 

 up particles of food, and a gizzard or grinding-mill, as it might be described, 

 from its thick walls and content of stones, swallowed by the bird for the actual 

 purpose of grinding its food. Following the digestive apparatus on farther 

 through its tortuous windings, we discover that as soon as all of the use- 

 ful parts of the food-materials in the stomach have been broken up and 

 passed on into the blood to be circulated throughout the body, the refuse or 

 non-usable parts, are rapidly pushed along out of the food-tube to make room 

 for a fresh supply. This well-nigh perfect system of digestion insures to the 

 bird the ability to produce, by means of an unusually large amount of food, 

 the immense motor-power which it requires for its daily activities. Could we 

 examine in detail this digestive outfit, we should understand far more clearly 

 the value of birds as the friends of man and the guardians of forests and fields. 

 At the same time, we should be more than ever impressed with Nature's 

 ability to perfect a plan in a special manner for a particular purpose. Although 



