my study about this moulting or changing of feathers?"

"Yes, I do," said Rap and Nat together. "Most birds have two coats a
year, and the male's is the brighter," continued Nat eagerly, proud to
show that he remembered. "The one that comes out in the spring is the
gayest, so that his mate shall admire him and when this coat comes he
sings his very best and--"

"Stop and take breath, my boy," laughed the Doctor; "there is plenty of
time. Why do we think that the male has the gayest feathers--do you
remember that also?"

"No, I've forgotten," said Nat.

"I remember," cried Rap; "it is to please the female and because she
sits so much on the nest that if her feathers were as bright as the
male's her enemies would see her quicker, and when the little birds
hatch out they are mostly in plain colors too, like their mother."

"Oh, I remember that now," said Nat. "And after the young are hatched
and the old birds need new coats, they keep rather still while they shed
their feathers, because they feel weak and can't fly well."

"Then when the new feathers come they are sometimes quite different from
the old ones, and seldom quite so bright--why is this, Nat?" asked the
Doctor. But Nat could not think, and Rap answered: "Because in the
autumn when they make the long journeys the leaves are falling from the
trees, and if they were very bright the cannibal birds would see them
too quickly." "Have I told you about the Bluebird, and how, though he
only sheds his feathers once a year, yet his winter coat is rusty and