The Bluebird, Martin, and Wren are three very popular birds.

They appreciate cosy homes and are grateful for the boxes built for them, though we know that before they had such things they must have nested in tree holes." "I wonder where the Chimney Swifts lived before there were any chimneys," said Rap, looking across the fields to where an old stone chimney stood--the only thing left standing of an old farmhouse.

Above this chimney, Swifts were circling in shifting curves, now diving inside it, now disappearing afar in the air.
"We think they must have lived in hollow trees as the Tree Swallows do now," said the Doctor; "but when House People began to clear the land they naturally cut down the dead trees first, and so the birds moved to the chimneys." "I used to call those birds Chimney 'Swallows,' but Olive says they are made more like Hummingbirds and Nighthawks than real Swallows," continued Rap.
"Nighthawks ?" said Nat.

"I thought Olive said Hawks were cannibal birds.
How are they relations of Swallows ?" "That is a mistake a great many people make," said the Doctor; "for the Nighthawk is not a real Hawk, but a shy bird, who has a rapid hawk-like flight, though it eats nothing but beetles, moths, and other insects.
Hark! Do you hear that cry high in the air ?" "As if something was saying 'shirk-shirk' ?" said Nat.
"Yes; that is a Nighthawk on its way home.

Look! he is over us now, and you can see two large white spots like holes in his wings.