46 AN ECONOMIC STUDY OF FIELD MICE. 
species — the Cooper and sharp-shinned — destroy so many birds and 
poultry as to far outweigh any good they may do. If legislation 
against hawks is needed, which is more than doubtful, careful dis- 
crimination should be exercised as to the species placed under baa, 
and corresponding protection should be given those that are of un- 
doubted benefit to the farmer. 
Owls. — Owls are preeminently enemies of mice. Their eyes are 
adapted to twilight and nocturnal hunting, and they prey mostly 
upon animals that are active after sunset. Noiseless of wing and 
possessed of sharp talons and much strength, they attack small mam- 
mals with great success. 
Owls, and also hawks and some other birds that eat small verte- 
brates by swallowing them entire, are unable to digest the bones, fur, 
and feathers. These are thrown up in the form of pellets, the bones 
being surrounded by fur and feathers. Much of our knowledge of 
the food of owls is derived from examinations of these pellets. 
The American barn owl (Strix pratincola) is rather common in 
the southern half of the United States, breeding as far north as forty- 
one degrees. In part of its range field mice are common and it preys 
upon them to a considerable extent. Examinations of 39 stomachs 
of barn owls were made b} T Doctor Fisher. Of these, 1 had eaten a 
domestic pigeon; 3, other birds; IT, mice; 17, other mammals; 4, 
insects; and 7 stomachs were empty. Meadow mice were found in 
9 of the stomachs. The mammals eaten, other than mice, were chiefly 
ground squirrels (spermophiles) and other injurious species. 
Doctor Fisher records the results obtained from an examination 
of 675 pellets of the barn owl collected at Washington, D. C. They 
contain remains of 1.731 rodents, 50 insectivorous mammals, 32 birds, 
and 2 frogs. The rodents were mainly rats (Jlus norvegicus), house 
mice (Mus imtsculus), and meadow mice (Microtus). Of the last 
there were 1,123 skulls, or an average of almost 2 to each pellet. a 
Doubtless similar investigations in California, where these owls are 
common, would show that there spermophiles are the chief food. 
The habits of the European barn owl [Strix aluco) serve to illus- 
trate further the usefulness of our own bird. Dr. Bernard Altum, 
a German naturalist, in 1863 recorded the results of examinations of 
703 pellets of the barn owl. He found remains of 16 bats. 933 
rodents, 1,479 shrews, and 22 small birds (19 of which were spar- 
rows). Of the rodents 693 were voles.^ Later (1867) he published 
the results of examinations of 360 additional pellets, making 1.063 
in all. The total sIioavs 2.151 insectivorous mammals, and 1,801 
rodents, of which 1.284 were voles.' 
a Science. X. S., vol. X pp. 623-624, Apr. 24. 180(1 
t> Journal fur Ornithologie, vol. 11. pp. 41-4(5. 217-219. 1863. 
c Zoologische Garten, vol. 8. pp. 263-264, 1867. 
