66 BULLETIN 621, U. S. DEPARTMENT OF AGRICULTURE. 



by three of four nestlings from the District of Columbia, as frag- 

 ments of the shell made up nearly 17 per cent of the stomach contents. 

 A discussion of the economic aspects of this part of the crow's food 

 habits is presented under " Food of Adult Crows " on page 36. 



SMALL MAMMALS. 



The efficiency of the crow in the control of mammal pests, in which 

 it ably supplements the work of birds of prey, is occasioned largely 

 by the food habits of the nestlings. "Over a twelfth (8.83 per cent) 

 of the food of young crows consists of mammals, the major portion 

 of which (6.22 per cent) was found to be injurious rodents. Re- 

 mains of mammals were discovered in 378 of the 778 stomachs, and 

 of these 145 contained the pests mentioned. 



As in the case of the parent birds, cottontail rabbits are the favorite 

 mammal food of young crows, being found in 67 stomachs. Nest- 

 lings secured in Kansas were especially well fed on cottontails. At 

 times all or nearly all members of a brood would have their stomachs 

 distended with such food. Five partly feathered young of the same 

 nest secured at Onaga in early May had all fed on one or more 

 rabbits, which formed an average of 65 per cent of their diet. Each 

 one of another brood of five from the same place also had partaken 

 of a cottontail, but in this case the remains formed about half the 

 stomach contents. Two more broods of three and four each had 

 their stomachs nearly two-thirds full of such food. In several other 

 instances also the remains of cottontails appeared in all the stomachs 

 of one brood, but in none did they constitute over half the food. It 

 frequently happened that each member of a brood had to be exam- 

 ined before conclusive evidence as to the origin of the flesh or hair 

 which occurred in all could be obtained. The young of these mam- 

 mals are torn to pieces before being fed to nestling crows, so that the 

 investigator is often compelled to postpone definite identification 

 of the food of a series of stomachs until the one containing a tooth, 

 parts of a skull, or other diagnostic bones is opened. 



Meadow mice (Microtus) were present in 17 of the 778 stomachs. 

 In three broods of three each these rodents were eaten by all indi- 

 viduals, forming 36, 14, and 12 per cent, respectively, of the broods' 

 food. White-footed mice (Peromyscus) occurred in 15 stomachs. 

 These entered into the food of all ten individuals of three broods. 

 In the case of one of the broods of three the remains of white-footed 

 mice formed nearly two-thirds of the stomach contents : in the brood 

 of four they constituted 62 per cent. In the stomach of one nestling 

 of a brood of five was found the entire body of a newly born Pero- 

 myscus, which doubtless had been dug from its nest. House mice 

 (Mus musculus) were found in two stomachs, a jumping mouse 



