VALUE OF BIRDS TO MAN. 



49 



The Time required for Assimilation of Food. 

 If we assume that the stomach and oesophagus of a young 

 Crow can contain but an ounce of food, then the bird would 

 be required to digest from eight to twelve meals a day, 

 according to its appetite and opportunity. The question at 

 once arises, How can any digestive system complete such a 

 task? Experiments were made with our young Crows to 

 determine the time required for 

 digestion. The birds were kept 

 without food until the stomach 

 and intestines were empty. 

 They were then fed insects' eggs, 

 in the belief that some parts of 

 the shells would escape the grind- 

 ing processes of the stomach and 

 be voided in the excreta. Sub- 

 sequent occurrences justified this 

 belief. Ten experiments of this 

 kind were made with the two 

 birds. 



From the time when the birds 

 began to feed until the time when the first eggshells were 

 dropped in the excreta there elapsed, on the average, one 

 hour, twenty-nine minutes and forty-five seconds. The 

 shortest time was forty-eight minutes, and the longest one 

 hour and fifty-four minutes. This, it should be noted, was 

 not merely the time that the food remained in the stomach, 

 but the full interval occupied in digesting and assimilating 

 it, for Avithin this period at least a part of the food had 

 passed the entire digestive tract. 



In most cases all evidence of the food used in the experi- 

 ment had disappeared from the excreta in from two to two 

 and one-half hours. If we contrast this with the slower 

 digestion of man, we shall see how birds readily dispose of 

 more meals each day than a man is capable of digesting. To 

 learn how long food remains in a Crow's stomach, it would be 

 necessary to kill a large number of Crows, each being killed 

 at a longer or shorter interval after it had filled its empty 



Fig. 23. 



- Young Crows, well 

 fledged. 



