34 THE BROWN RAT IN THE UNITED STATES. 



NATURAL ENEMIES OF THE RAT. 



The extent to which predatory mammals and birds feed upon ro- 

 dents should be more generally understood. Probably the greatest 

 factor in the increase of rats, mice, and other destructive rodents 

 in the United States has been the persistent killing off of the birds 

 and mammals that prey upon them. Too often the slaughter is 

 based upon ignorance of the animal's real economic value. Ani- 

 mals that on the whole are decidedly beneficial are habitually de- 

 stroyed because they occasionally transgress. Thus, warfare is 

 made on the skunk and many kinds of hawks and owls that 

 occasionally destroy a chicken or a game bird but which habitually 

 subsist upon harmful insects and rodents. Among the natural 

 enemies of the rat are the larger hawks and owls, skunks, foxes, 

 coyotes, weasels, minks, and a few other mammals. To these must 

 be added the domestic dogs, cats, and ferrets. 



HAWKS. 



Several kinds of hawks feed on rats, usually during the season 

 when the latter infest the fields; for hawks, because of persecution, 

 do not often stay about farm buildings. Hence, ordinarily hawks 

 have few opportunities to prey on these denizens of house and barn. 



In open fields, however, rats often come out in daytime, espe- 

 cially in early morning and late afternoon. Hawks are then on 

 the lookout for prey, and many a rat is killed by them. The species 

 of hawks that most commonly feed upon rats are: The buzzard 

 hawks (Buteo), including the red-tailed (Buteoborealis and subspecies), 

 the red-shouldered (B. lineatus), the broad-winged (B. platypterus) , 

 and the Swainson (B. swainsoni); the rough-legged hawks (ArcM- 

 buteo), two species; and probably the marsh harrier (Circus Tiud- 

 sonius) . 



OWLS. 



In destroying rats owls are more efficient than hawks, because 

 they hunt at night, when the rodents are most active. All American 

 owls except the most diminutive species kill rats. Even the little 

 screech owl (Megascops asio) often feeds upon the young. 



Of all our owls, the barn owl (Strix pratincola) stands at the head 

 in destructiveness to rats, since it often makes its home about farm 

 buildings. Dr. A. K. Fisher, of the Biological Survey, has examined 

 the pellets, or castings, of a pair of barn owls that live in the tower 

 of the Smithsonian Institution in Washington and found in them 

 skulls of 172 rats (Mus norvegicus). In addition, these birds had 

 destroyed 1,285 field mice and 452 house mice. 



Dr. John I. Northrop found a nest of the barn owl on Andros 

 Island, Bahamas, which held two young birds not yet. able to fly. 

 The ground around the nest was covered with pellets which contained 



