IS UNIVERSITY OF COLORADO. 



they were, at least to some extent, feeding upon the corn, but field observa- 

 tion alone could not inform the observer of the proportion of cutworms and 

 other pests taken to pay for the corn. If the robins were seen picking cher- 

 ries, it was easy to infer that their food is cherries, with no knowledge of 

 the fact that to some extent they made the cherries possible by their police 

 work in the prevention of the ravages of insects. 



From innumerable observations of many species, naturalists are able 

 to tell much about the food habits of a given species by its physical structure. 

 The long legs, long neck and spear-like beak of the heron family are cor- 

 related with the food habits of the family. So, too, the ducks have feet and 

 bills suited to their feeding habits. The cracking of weed seeds, so easy for 

 the finches, with their stout, conical bills, would be quite impossible for the 

 warblers, yet people who suppose the yellow warblers to be wild canaries 

 attempt to feed them with bird seeds such as are placed in the canary cages. 

 The woodpecker easily sinks a shaft to the tunnel of a tree-boring insect 

 and extracts the dainty morsel for his breakfast, while a dove would have a 

 sad time trying to get the troublesome borer. 



But after all, the final test is an examination of the actual contents of 

 the stomachs. From a decision based upon such evidence, providing a suf- 

 ficient number of stomachs are examined with care, there is no appeal. It 

 has often been asserted that certain insects are not taken by birds because 

 they are concealingly colored and escape observation; that others are not 

 taken because they are protected by bristles or other armor; that others, 

 such as blister beetles and stink bugs, are not taken because they possess 

 irritating or nauseating secretions ; but actual examination of the stomach 

 contents of birds has shown conclusively that all these types of insects are 

 taken regularly and in fair quantities by some species of birds. 



In the literature of economic ornithology it is customary, for the sake 

 of convenience, to include under the term stomach, the crop (of such species 

 as have crops), the throat, etc. In case of many insects, even small frag- 

 ments of the hard parts remaining after the soft parts have been digested, 

 may be identified. The work of sorting over miscellaneous material and 

 identifying it, often under a lens or even with the aid of a comp'ound micro- 

 scope, is extremely tedious. The United States Biological Survey, a bureau 

 or division of the Department of Agriculture, has been preeminent in this 

 work, as may be seen by a 'glance at the bibliography accompanying this 

 paper, though there have been and now are a number of independent work- 

 ers of note in this field of study. With no actual figures of recent date at 

 hand, it is safe to say that probably between 50,000 and 100,000 bird stomachs 

 have been examined in the United States alone (41). 



The net result of all this work is to convince naturalists that nearly all 

 native species of birds should be protected. 



(41) McAtee, W. L., Methods of Estimating the Contents of Bird Stomachs, The 

 Auk, Vol. XXIX, pp. 449-464, 1912. 



