134 CO ACTION: THE INTERRELATIONS OF ORGANISMS 



the small animals captured. Both live chiefly upon small mammals, 

 birds, and reptiles; about two-thirds of each include insects in the 

 diet. The osprey or fish hawk lives entirely upon fish, and the bald 

 eagle largely so, while fish are a regular feature in the food of several 

 other hawks, but only one owl, the screech owl. The Cooper and 

 sharp-shinned hawks prey chiefly on larger wild birds, as do the 

 American and western goshawks. A few species such as the pigmy 

 owl and the sparrow hawk are mainly insectivorous, 314 out of 410 

 stomachs of the latter containing insects; 129, small mammals; and 

 70, small birds (cf. Henshaw, 1921). 



Among the few carnivorous birds in other North American families, 

 the kingfisher prefers fish, but his tastes cover lizards, frogs, insects 

 and crustaceans. The shrike is said to feed principally upon grass- 

 hoppers, but it captures many small mammals and some birds ; its lack 

 of talons causes it to impale its large prey, and it is also supposed to 

 use this device for al fresco storage. The road runner alone of the 

 bird carnivores employs a mixed diet, adding cactus fruits to a long 

 list of animals ranging from mice and small birds to snails and 

 caterpillars. 



The examination of more than a thousand pellets of the marsh 

 hawk in Florida disclosed that this bird lives largely upon cotton 

 rats in the particular region. The number for this rat was 925 to 21 

 for the cottontail and 7 for the common mole. Of more than 40 

 species of birds taken, only 3 were found in more than 10 instances, 

 namely, song sparrow, 64; meadow lark, 26; savanna sparrow, 23 

 (Stoddard, 1931). By contrast. Cooper's hawk yielded 38 stomachs 

 with poultry and game birds, 60 with other birds, and 12 with mam- 

 mals, out of a total of 123 (Henshaw, 1921). 



First and last, the raptores take a prodigious toll of the smaller 

 mammals, birds, reptiles, and insects, both in number and species. This 

 is strikingly shown at the time of lemming migrations, as well as in 

 other cyclic concentrations, but definite knowledge of the direct effect 

 upon the composition of the biotic community is exceedingly difficult 

 to secure. This is even truer of the indirect influence upon the plant 

 matrix, but, in terms of seed- and fruit-eating coactees, this may well 

 be considerable and in some instances locally decisive. 



The Prey of Insectivorous Animals. Two groups occur, namely, 

 cursorial and aerial. Those possessing powers of flight include many 

 species of small birds, bats, and some insects. Of the birds, prob- 

 ably the swifts and creepers are the only common families that 

 are exclusively insectivorous, though the flycatchers, kinglets, goat- 

 suckers, swallows, vireos, wood warblers, and wrens are predominantly 



