INVESTIGATION IN ECONOMIC M A M M A L O G Y 183 



were available, taken at various seasons of the year at many localities, 

 one could closely approximate the average food of the species as a 

 whole. Just this has been done with many species of birds. Some prog- 

 ress has been made along this line with mammals, but the work is now 

 in its infancy. We must face one difference that handicaps the mam- 

 malogist. Birds do not chew their food, but mammals do. In the stom- 

 achs of insectivorous birds many insects may be found in condition for 

 positive identification. In the stomachs of bats the insects are usually 

 finely comminuted, often making only very general identifications pos- 

 sible. Hawks and owls swallow mice whole. Weasels do not swallow 

 their prey whole, except the smaller kinds. This difficulty, however, is 

 not as "great as has often been supposed, and the future should see prog- 

 ress along this line of investigation accelerated. Dixon says: 



Of course, we recognize at once that fur-bearing mammals have series of sharp 

 teeth with which to rend and cut their prey, while hawks and owls have only 

 hooked beaks. People have assured me that it would be impossible to identify 

 stomach contents of fur-bearing mammals because, they were confident, the 

 food would be too well masticated. This has not proved to be the case. I have 

 found the contents of wild-cats' stomachs to be quite similar to the stomach 

 contents of horned owls. From my own experience I know that there are 

 relatively few carnivorous mammals in which the identification of food re- 

 mains is not feasible. I have found the food of the otter chewed the finest and 

 hence most difficult to identify. Minks are much easier than otter. Bobcats and 

 mountain lions just chop up their food and swallow it in chunks, as do also 

 coyotes and foxes. Even beavers and muskrats do not chew their food as finely 

 as we might suppose, and identification is, even in their cases, not usually 

 difficult. I have found the following to be the best clues by which stomach 

 contents of fur-bearers may be identified. Mammal remains can be identified 

 by the presence of teeth, feet, claws and hair. Birds may be best told by feet, 

 claws and bills. Feathers are sometimes difficult to identify. The hard parts of 

 insects, particularly mouth parts, wings and legs, assist in identification. For- 

 tunately in insects the species involved are for the most part of large size, well 

 known, and hence easily identified. The skin and feet of toads and frogs help 

 in identification, as do also the scales of fishes. 1 



Having determined the facts concerning the food of a given species, 

 in order to reach a safe conclusion concerning the economic status 

 of the species under investigation, its food habits must be considered 

 in the light of all that is known of the intricate interrelations of the 

 various organisms in its diet, their respective food habits, their useful- 

 ness or harmfulness, their abundance and so forth. A balance must 

 also be struck between its economic status arising from its food habits 



1 Dixon, Food predilections of predatory and fur-bearing mammals, Journ. Mam- 

 malogy, vi, 34, IQ25- 



