s, but where
these are not to be had they enter the orchards and soon become known as
enemies of the farmer.

A careful examination of the harm done by birds leads to the belief
that the damage is usually caused by a very large number of one species
of birds living in a small area. In such cases so great is the demand
for food of a particular kind that the supply is soon exhausted, and the
birds turn to the products of the field or orchard. The best conditions
exist when there are many varieties of birds in a region, but no one
variety in great numbers, for then they eat many kinds of insects and
weeds, and do not exhaust all the food supply of one kind. Under such
circumstances, too, the insect-eating birds would find plenty of insects
without preying on useful products, and the insects would be held in
check, so that the damage to crops would be slight.

The following are examples of the food eaten by birds and the good that
they thus accomplish to man:

During the outbreak of Rocky Mountain locusts in Nebraska, a scientific
observer watched a long-billed marsh wren carry thirty locusts to her
young in an hour and the same number was kept up regularly. At this
rate, for seven hours a day, a nest-ful of young wrens would eat two
hundred and ten locusts a day. From this he calculated that the birds of
eastern Nebraska would destroy daily nearly 163,000 locusts.

A locust eats its own weight in grain a day. The locusts eaten by the
baby birds would therefore be able to destroy one hundred and
seventy-five tons of crops, worth at least ten dollars a ton, or one
thousand seven hundred and fifty dollars.

So we see that birds have an actual cash value on the farm. The value of
the hay crop saved by meadow-larks in destroying grasshoppers has been
estimated at three hundred and fifty-six dollars on every township
thirty-six miles square.

An article contributed to the New York _Tribune_ by an official in the
Department of Agriculture estimated the amount of weed seeds annually
destroyed by the tree sparrow in the state of Iowa on the basis of
one-fourth of an ounce of seed eaten daily by each bird. Supposing there
were ten birds to each mile, in the two hundred days that they remain in
the region, we should have a total of 1,750,000 pounds, or eight hundred
and seventy-five tons, of weed seed consumed in a single season by this
one species in the one state. In a thicket near Washington, D. C. was a
large patch of weed