“Nobody seems to know why she doesn’t; but there’s the fact.  When the cuckoo has laid an egg, she carries it in her wide, gaping mouth, and puts it into the nest of another bird that she has chosen for it.  When the egg is hatched, the young cuckoo grows so fast that he wants all the nest to himself.  He turns the other young birds that have been hatched with him out of the nest, and the true parents of these little birds have to spend all their time in feeding the cuckoo.  It takes a great deal to feed him, because he grows so fast, and is so much larger than they are.  They don’t seem to mind it though.—­Those pale-green eggs with dark-brown spots belonged to a rook’s nest in the elm-tree at the bottom of the garden.  There’s a curious story about those rooks down there, for they have not been there long.  There is an old rookery belonging to the Rectory close by our house; and one day the rooks from there came to our elm-tree.  It was in the spring.  At last they came frequently, and chattered, and cawed, and flew round and round, as if they did not know what to do about building their nests in it.  By-and-by their visits ceased, and they built their nests as usual in the Rectory trees.  That very summer, during one still night, a large branch, almost a third of the elm-tree, fell to the ground.  The rooks seemed to know that the tree was not safe, and so they would not build in it.  That was two years ago; and this spring they have begun to build, and there are several nests now in our elm-tree.  It is most interesting to watch the ways of rooks; they seem to have a lot of business on hand.  There is another rookery in the town, in the garden of Mrs. Cross, a friend of my mother’s.  Rooks always leave the town rookeries for the country as soon as their young ones are able to fly.  Now Mrs. Cross noticed that her rooks, after they had gone to the fields, always came back each morning quite early to look after their nests.  They stayed a little while to talk over matters; then they flew back again to the fields.  One very stormy morning she noticed that instead of the whole flock coming and alighting, one solitary rook ventured through the wind and rain, flying round and round the trees without settling, and then flew back again to the others to give his report that all was right in the old home.”

“What clever birds they must be!” said Mary.

“They are,” said Tom.  “There are lots of stories about rooks, but what I have told you happened under our very eyes.—­I have a sparrow-hawk’s egg here, white, spotted with brown.  It was given to my father by a man for me.  There are not many of these birds about here.”

“Oh,” said Jack, “I wish I could get a collection of birds’ eggs!”

“It is almost too late in the season now,” said Tom.  “Still, you might get some from late nests.  I can spare you some from mine, to make a beginning.  I know a young fellow, who lives about a half-mile off, who has a large collection of eggs.  We’ll go and see him one Saturday afternoon.  He is sure to have some to give away, for he is always adding to his store, and he is very good-natured.”