BIRDS OF A MARYLAND FARM. 



I.— INTRODUCTION. 



The principal method used by the Biological Survey in investigat- 

 ing the food habits of birds is examination of the contents of stomachs, 

 the material for which is obtained from all parts of the United 

 States. In the case of each species the separate data accumulated by 

 examining as many stomachs as possible are tabulated and show the 

 food of the bird in question to consist of various proportions of cer- 

 tain elements. This method, combining as it does data from many 

 parts of the country, gives results necessarily somewhat composite, 

 but certainly trustworthy, and shows to what extent a bird eats 

 fruit, grain, or insects, thus furnishing a comprehensive and detailed 

 knowledge of food habits that probably could not be obtained by any 

 other available means. 



In a study of local conditions, however, general conclusions regard- 

 ing the utility of a bird based on data from perhaps a score or more 

 of States may sometimes require modification. For instance, from a 

 study of the smaller herons from material collected from North, South, 

 East, and West the conclusion would be drawn that they live on food 

 of no economic value and are therefore unimportant species. But 

 a study of these birds in the State of Louisiana alone shows them to 

 be highly useful, for here they prey on crayfish, which, by tunneling 

 through the levees, cause great damage to crops by flood. In similar 

 ways the relations of birds to a certain locality or particular farm 

 can not always be exactly tested by conclusions drawn from a large 

 range of territory.' The exact damage to crops is not revealed by 

 stomach examination. A bird may have punctured several grapes 

 in each of a hundred clusters and yet betray to the microscope no 

 sign of its vicious habit. On the other hand, a bird may be con- 

 demned as injurious because it is found to have eaten berries or grain, 

 although, as a matter of fact, it has taken the berries from wild plants 

 and gleaned the grain after harvest. Then, too, the material exam- 

 ined at the Department is not usually accompanied by notes of the 

 available supply of fruits, seeds, and insects present at the places 

 where the birds were collected. Such information would be a sig- 

 nificant supplement to the results of stomach examination. The faults 

 of a fruit-eating bird might be condoned if it were found to rob the 

 garden and orchard only when the thicket and pasture were barren. 

 And the value of birds as insect destroyers in any particular locality 



