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. Ee- 
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- 
myseus, which doubtless had been dug from its nest. House mice 
(Mus musculus) .were found in two stomachs, a jumping mouse 
