Owls as destroyers of mice are deserving of special mention. Not one of
our American owls, unless it be the great horned owl, is to be classed
as noxious. Especially beneficial are the short-eared, long-eared,
screech, and barn owls. All these prey largely upon field mice, and
seldom harm birds. Unfortunately, the short-eared and barn owls, which
are the more useful species, are not plentiful in the sections most
seriously infested by field mice.
The short-eared owl, while widely distributed, is not abundant, except
locally, within the United States, but wherever field mice become
excessively numerous these owls usually assemble in considerable
numbers to prey upon them. Examinations of stomachs of these owls show
that fully three-fourths of their food consists of short-tailed field
mice.
The barn owl is rather common in the southern half of the United States
and breeds as far north as the forty-first parallel of latitude. That
mice form the chief diet of this bird has been demonstrated by Dr. A.
K. Fisher, of the Biological Survey, through examination of stomachs
of many barn owls and also of large numbers of pellets (castings from
their stomachs) found under their roosts. In 1,247 barn-owl pellets
collected in the towers of the Smithsonian Building in Washington,
D. C., he found 1,991 skulls of short-tailed field mice, 656 of the
house mouse, 210 of the common rat, and 147 of other small rodents and
shrews. Very few remains of birds were found. Figure 7 illustrates the
contents of some of these pellets.
[Illustration: FIG. 7.--Field-mouse skulls taken from pellets
found under owl roost in Smithsonian tower, Washington, D. C.]
In 360 pellets of the long-eared owl Dr. Fisher found skulls of 374
small mammals, of which 349 were meadow mice. Stomach examinations give
similar testimony to the usefulness of this bird.
The common screech owl, in addition to feeding mainly upon mice,
destroys also a good many English sparrows. Its habit of staying in
orchards and close to farm buildings makes it especially useful to the
farmer in keeping his premises free from both house and field mice.