134 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



when young. Mountain-beavers also are rather large and are inacces- 

 sible to any but owls, of which the great horned owl contributed our 

 only record of their being eaten. 



The large number of determinations of members of the squirrel 

 family, cover, it must be recalled, such diverse groups as the spermo- 

 philes, prairiedogs, groundhogs, tree squirrels, and chipmunks. There 

 are only two records of the groundhog, a very large rodent, one being 

 captured by a goshawk and the other by a golden eagle. The number 

 of identifications (15) of the chiefly nocturnal flying squirrels seems 

 as large as could be expected. The cryptically colored rabbits are 

 exceedingly common and live fully exposed to predacious birds, fac- 

 tors which go far toward accounting for the very large number of 

 records of their being eaten. The remaining families in the list all 

 consist of animals so large that only a few of the most formidable 

 birds can prey upon them, and then only upon the young. There are 

 observations of such occurrences, but it so happens that our records 

 of stomach contents do not include any of them. 



Total number of identifications of mammals, 3,151 ; percentage of 

 identifications among those of all vertebrates, 23.6542 ; percentage of 

 species in this class among those of all nearctic vertebrates, 13.5743. 



Other enemies. — Fishes have few opportunities to capture mam- 

 mals, but trout have been known to feed upon meadow mice and 

 lemmings, and it is probable that other highly predacious fresh-water 

 fishes occasionally get small mammals that venture near or in the 

 water. The bullfrog is the only one of our amphibians known to eat 

 mammals, an occasional mouse falling to its lot. The snapping turtles 

 also get some mice and sometimes even capture animals as large as 

 rabbits. Among snakes we find many habitual predators upon mice 

 and other small mammals. Some results of studies of the food of 

 snakes by the Pennsylvania Division of Zoology may be briefly cited: 

 Pilot snake, mice 22 per cent of the diet, squirrels 1 1 per cent, weasels 

 4 per cent ; black snake, mice 26 per cent, rabbits 4 per cent, other 

 mammals 7 per cent; milk snake, mice 71 per cent, other mammals 

 II per cent; copperhead, mice 41 per cent, shrews 4 per cent, other 

 mammals 8 per cent. In the case of the timber rattlesnake, mice, rats, 

 and rabbits composed nearly the whole diet. This is known to be true 

 also of most of our venomous snakes. 



The worst foes of mammals, however, are their own kind, and the 

 diversity of their predatory habits may be indicated by brief refer- 

 ences to their mammal prey. Opossums take limited numbers of small 

 mammals, while raccoons and skunks prey more extensively upon 



