.

"That is the Kingbird," said the Doctor; "one of the most useful of the
insect-catchers. Instead of living on honey-bees, as many people think,
he eats very few of these, but kills instead thousands of the bad
robber-fly, which is the honey-bee's worst enemy. This bird is really
king of the air and of all fly-catching birds. See how graceful his
flight is, and how easily be moves!"

"Why did he go away last fall?" asked Nat. "Does he feel the cold
weather very much?

"He does not stay in the United States until the weather is cold enough
to dull him; but he has to move away for another reason. The same reason
that forces so many birds to leave us--he must follow his food. This
food consists of insects--different kinds of flies, ants, and
grasshoppers, which disappear or die as the air grows cold.

"Rap, have you ever noticed the difference between the sounds in a
spring night and a night in autumn? In spring the air is humming with
the calls of all sorts of insects, but in autumn it is silent, and even
the crickets have stopped chirping.

"So about the last of September our Kingbirds, who live everywhere in
the United States, gather in flocks, start to find a place where insects
are still stirring about, and fly southward, following the sea-coast and
the great rivers for paths. Those from the eastern part of the country
stop in Central America or fly on to South America, and those from the
western part often stop in Mexico."

"But how can they fly so far?" said Nat; "it's hundreds of miles; and
how do they find the way?"

"The flight of a bird is a wonderful thing, my boy. He spreads those
frail wings of his, and launches into the air, up, up, above trees and
steeples, then on and on, being able to fly several hundred miles
without resting. Some birds, when the wind aids them, cover more than a
hundred miles in a single hour.

"As to the way, the eye of the bird is like a telescope. It magnifies
and sees from very far off. Flying through the upper air the bird
watches the line of coast and river, and the instinct that is placed in
him says, 'Follow these.' So he follows them, remembering that by doing
so he has found a place of safety in other seasons. All through the
spring and all through the autumn birds take these mysterious
flights--for so they always seem to House People, as flock after flock
gathers and disappears. You can watch them sometimes passing by day so
high in the sky that they seem like dus