"It is too long a walk for little sister, but you must remember everything that you see and hear, and tell her about it. Don't forget the field-glass," said the Doctor, following the boys along the road where telegraph wires made bird-perches between the high poles.
"You said a lot of birds came last night," said Nat to Rap; "but how do you know that they came last night and where did they come from?"
"I know they came last night because they were not here yesterday," answered Rap; "but I don't know where they came from, except that it must be from where it is warmer than it is here, because they went away just before it grew cold last fall. See, Doctor, there are some of them now on those fence rails and more up on the telegraph wires. The miller calls them 'Bee Martins,' and says that they eat up all the honey-bees. Have they any other name--because I have never seen them catch bees?"
Nat looked at them first with the field-glass, then without it as they drew quite near the fence, and saw a fine bird, twice as long as his middle finger. Its back and wings looked dark gray; it was white underneath, with a touch of gray on the breast, and had a black tail, with white at the end of it. As Nat looked the bird raised a little tuft of feathers on top of its head, as if angry, flew into the air, giving a shrill cry, seized an insect, and returned to its perch.
"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.
