THE PRACTICAL VALVE OF BIRDS. 17 



beetles, disgorged the waste in 1 hour and 20 minutes, and when fed on a 

 mouse digestion required 3 hours (32). 



A young robin in captivity ate from 50 to 70 cutworms and earthworms 

 daily from May 21 to June 6, and on June 9, when the bird weighed exactly 

 3 ounces, it consumed 165 cutworms, which weighed altogether 5% ounces, 

 nearly twice the weight of the bird (33). Another robin on the 14th day of 

 its life ate 68 worms, which weighed 41% more than the bird (34). 



One snowy owl contained 14 white -footed mice and 3 meadow mice (35). 

 A golden eagle in captivity will consume 2 pounds of fresh meat daily (36). 

 A Cooper's hawk reared by Judd (37) frequently ate its own weight of food 

 in a day, and another, 6 weeks old, was observed by Roddy to devour S 

 English sparrows and a mouse in one day. One flicker stomach contained 

 5,040 ants and 2 others contained about 3,000 each (38). One quail stomach 

 contained 10,000 pigweed seeds, another contained 5,000 pigeon-grass 

 seeds (39). 



A given number of thousands of insects or seeds taken by a bird in a 

 week does not mean merely the destruction of so many insects or seeds, but 

 that those thousands and other thousands taken from week to week are 

 prevented from reproducing their kind and so multiplying by millions far 

 into the future. Likewise the destruction of a useful bird does not mean 

 merely one useful bird removed, but means the destruction of all possible 

 progeny of that bird. 



The various so-called protective devices of insects, such as concealing 

 coloration, defensive armor and offensive secretions, are unavailing as a 

 means of escaping their sharp-eyed enemies, the birds (40). 



METHODS OF INVESTIGATION 



The primitive method of investigating the food habits of birds was field 

 observation. While that method brought forth considerable accurate in- 

 formation, yet in many cases it inevitably led to incorrect conclusions. If 

 hawks were frequently seen to carry off chickens it would naturally lead to 

 the destruction of all hawks, without discrimination as to species. In fact, 

 the large hawks commonly called "chicken hawks" are not the chicken 

 hawks at all. If blackbirds were seen digging about the roots of sprouting 

 corn, it would naturally be inferred, and perhaps even demonstrated, that 



(32) Judd, Sylvester D., Birds of a Maryland Farm, U. S. Biol. Surv., Bull. No. 17, 

 p. 102. 



(33) Nash, Charles W., The Birds of Ontario In Relation to Agriculture, Ontario 

 Dept. Agric., 1898, p. 22. 



(34) Palmer, T. S., A Review of Economic Ornithology in the United States, U. S. 

 Dept. Agric., Yearbook for 1899, pp. 261-262, citing Treadwell, Proc. Boston Soc. 

 Nat. Hist., Vol. VI, pp. 386-399, 1859. 



(35) Fisher, A. K., Hawks and Owls from the Standpoint of the Farmer, U. S. 

 Dept. Agric., Yearbook for 1894. p. 226 ; Hawks and Owls of the United States in their 

 Relation to Agriculture, U. S. Dept. Agric., Div. Orn. and Mam., Bull. No. 3, p. 187, 1893. 



(36) Oberholser, Harry C., The North American Eagles and their Economic Rela- 

 tions, U. S. Dept. Agric., Biol. Surv., Bull. No. 27, p. 30. 



(37) Judd, Sylvester D., The Food of Nestling Birds, U. S. Dept. Agric., Yearbook for 

 1900, p. 429, citing Roddy, The Auk, Vol. V, p. 246. 



(38) Beal, F. E. L., Food of the Woodpeckers of the United States, U. S. Dept. 

 Agric., Biol. Surv., Bull. No. 37, p. 54. 



(39) Judd, Sylvester D., The Economic Value of the Bobwhite, U. S. Dept. Agric., 

 Yearbook for 1903, p. 195. 



(40) Beal, Agric. Yearbook for 1908, pp. 346-347. 



