“Isn’t it pretty?” said Nat; “so even and deep like a cup, and not at all ragged and mussy like a Robin’s nest.  There are a great many different kinds of nests, aren’t there, uncle?”

“Yes, the nests of birds are almost as different as their songs and other habits, and the higher the order the brood belongs to the better built is the nest.  The lower orders often only make a hollow in the ground or grass, but do not collect material and build in the true sense.  None such can be called architects.”

“What is an architect?” asked Nat, who thought it was a pretty big name for any sort of a bird.  “An architect, my boy,” said the Doctor, “is anybody who knows how to build anything as it ought to be built, to look the best and be the most useful, whether it is a house or a nest.”

“I wonder why nests are so different,” said Rap, looking down the lane toward the river where the sun was streaming in and so many little birds were flying to and fro that they seemed like last year’s leaves being blown about.

“Because, as the habits of the birds cause them to live in different places, and feed in various ways, so their homes must be suitable to their surroundings, and be built in the best way to protect the young birds from harm—­to keep them safe from House People, cannibal birds, and bad weather.

“The trim Thrushes and Sparrows, who are all brownish birds, and find their insect or seed food on or near the ground, build open nests low down in trees and bushes, or on the earth itself; but the gorgeous Baltimore Oriole, with his flaming feathers, makes a long pocket-shaped nest of string and strong plant fibres, which he swings high up in an elm tree, where it cannot be reached from below, and the leaves hide this cradle while the winds rock it.  He knows that it would never do to trust his brilliant feathers down by the ground.

“The frail Hummingbird has no real strength to fight enemies bigger than its tiny self, but it has been given for protection the power of flying as quick as a whizzing bullet, and courage enough to attack even a Kingbird in defence of its nest, which is a tiny circle of down, covered with lichens, and is so fastened across a branch that it looks like a knot of the limb itself.  The Woodcock you saw that snowy day, Rap, knows the protection of color and draws together for a nest a few leaves of the hue of her own feathers.  This nest and the bird upon it are so blended together that few eyes could separate them.”

“Some birds do not make any nests, but live in holes like squirrels and coons,” said Rap.  “Woodpeckers and all those.”

“There again the home is suited to the occupation of the bird,” said the Doctor; “for Woodpeckers are Tree Trappers, who find their food by creeping about trees and picking insects and grubs from the bark.  What more natural than that they should have a house close at hand in some tree whose wood is soft enough to be hollowed out?  You see they have a bill like a chisel for gouging out insects, and with this same tool they make their homes.”