"It seems as if I could almost hear the words he says," said Rap.

"Birds sing in many different tones," said the Doctor. "The Thrasher's
song is like some one talking cheerfully; the Meadowlark's is
flute-like; the Oriole's is more like clarion notes; the Bobolink
bubbles over like a babbling brook; while the dear little brown striped
Song Sparrow, who is with us in hedge and garden all the year, sings
pleasant home-like ballads."

"There are some birds that Olive told me can't sing a bit," said Nat,
"but only call and squeak. How do they ask their mates to marry them?"

"All birds have alarm cries, and a call-note that serves the same
purpose as a song, although it may not seem at all musical to us. We are
naturally more interested in that order of birds whose voices are the
most perfectly developed. These not only sing when they are courting,
but all the time their mates are sitting upon the eggs, and until the
young are ready to fly."

"Why do birds always build nests in spring?" asked Nat.

"I think because there is more for them to feed the little ones with,
than when it gets to be hot and dry," said Rap, "and it gives them time
to grow big and strong before winter comes, when they must go away."

"Quite right, Rap, and it also gives the parents a chance to shed the
old feathers that have been worn by rubbing on the nest, grow a new,
thick, warm coat for winter, and rest themselves before they set out on
their autumn journey. Do you remember what I told you that rainy day in