6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



ANIMALS EATEN BY NEARCTIC BIRDS 

 Data Cited and How Obtained 



The main body of data used herein consists of the records of 

 animals identified in the contents of the stomachs of about 80,000 

 nearctic birds examined in the United States Biological Survey since 

 1885. These stomachs represent a wide range of species of all of 

 the families of birds occurring in the region ; the birds were collected 

 at all seasons and in practically all parts of nearctic America. While 

 not evenly distributed in any of these senses, the collection is very 

 satisfactory for the purpose in hand, and yields a mass of precise 

 information on bird food that far surpasses anything of the kind 

 available elsewhere. 



A word about the methods of investigating bird food may be 

 desirable. The gizzards of birds, together with the gullets or crops 

 when they contain food, are received chiefly from persons collecting 

 birds for some other scientific purpose, although in some cases they 

 are especially obtained to throw light on the relations of birds to some 

 crop, or useful or injurious animal. They are preserved usually with 

 formalin in the field and in alcohol after receipt at the laboratory. 

 Contents of a stomach being examined are removed either wet or dry 

 as best fits the particular case and transferred to watch glasses or 

 small white blotters for sorting and identification of the material 

 under compound binocular dissecting microscopes. A great deal of 

 the analysis is done at a magnification of 8 diameters but special 

 study of difficult subjects is continued when necessary under higher 

 powers. 



At this point it may be well to comment on the popular misconcep- 

 tion that anything found in a bird's stomach necessarily is ground 

 up and in all but unrecognizable state. As a matter of fact the reverse 

 is true. Most birds swallow their food whole ; consequently in any col- 

 lection of birds a certain proportion will have swallowed some food 

 items just before death. These things often are in perfect condition ; 

 they may be, and sometimes are, used for cabinet specimens. The 

 nearly or quite whole objects usually furnish clues to the fragmentary 

 material, and in the great majority of cases it is possible to sort out 

 completely all components of the food. It is the exception when the 

 finely ground food remains defy separation and identification. De- 

 terminations are carried as far as practicable ; each member of the 

 stafif of analysts is a specialist in some line and they cooperate freely ; 

 specimens defying their combined cft"orts, if in fair or better condi- 

 tion, are submitted to advanced investigators elsewhere. The records 



