16 



SPERMOPHILES OF THE MISSISSIPPI VALLEY. 



that they wove actually able to kill adult squirrels, I trapped several 

 and placed them alive (they had been caught in a wire trap and were 

 not at all injured) in a room with a pair of these owls. As soon as no- 

 ticed by the latter, one of them would fasten his talons into the 

 squirrel's back and, with a few well-directed strokes of its beak, break 

 the vertebra? of the neck and eat the head of the squirrel, often before 

 the latter was quite dead; yet the remainder of the body was usually 

 left and devoured later. I was surprised to see how easily they killed 

 these squirrels, which made scarcely any resistance." (Ornithologist 

 and Oologist, Vol. VI, 1881, pp. 41-42.) 



So less than 10 of the 73 species and subspecies of hawks and owls 

 found in the United States and British America are known to prey on 

 the various members of the genus Spermophilus. The following species 

 have been reported to feed on these animals, and more careful observa- 

 tions will undoubtedly increase the list : 



Archibuteo ferrugineus. 

 Aquila chrysaetos. 

 Haliwetus leucocephalus. 

 Falco mexicanus. 



In our investigations of the food of hawks and owls the remains of 

 spermophiles were actually found in the stomachs of 22 specimens 

 representing 7 species of these birds. The total number of stomachs 

 of these species examined was 981. This proportion (about 2^ per 

 cent) does not represent the true percentage of spermophiles in the 

 bird's food inasmuch as a very large number of the stomachs were ob- 

 tained from birds killed in the eastern United States where spermo- 

 philes do not occur. Thus, in a total of 562 stomachs of the redtail (Buteo 

 borealis) and its subspecies, 477 were taken in States east of the range 

 of Spermophilus; and of 127 stomachs of the great horned owl (Bubo 

 rirginianus) only 53 were taken within the range of this genus, and 

 of these 11 were empty. If, on the other hand, all empty stomachs 

 and all those taken outside the range of Spermophilus are discarded (a 

 total of 799), the percentage containing spermophiles is increased from 

 2J to L2; while 23 per cent of the marsh hawks examined, 25 per cent 

 of r lie prairie falcons, and 40 per cent of Harris' hawks were found to 

 have fed on these animals, as shown in detail in the following table: 



HAWKS. 



OWLS. 



Circus hudsonius. 

 Accipiter cooperi. 



Strix pratincola. 

 Bubo v. subarcticus. 

 Nyctea nyctea. 

 Surnia ulula caparoch. 

 Speotyto c. hypogaa. 

 Glaucidium g. californicum. 



Parabuteo u. harrisi. 



Buteo b. krideri. 

 Buteo b. calurus. 

 Buteo swain soni. 



