in dog's language means "Yes."

So they romped away to the barnyard to chase the frightened White
Wyandottes.

That was not a good thing for the chickens but it was a good thing for the
children. For if the dogs had not run away they might have missed something
very wonderful.

What do you think it was?

First they heard pretty strains of music. It was something like a song and
something like a whistle.

They looked up in the elm tree.

There, shining among the dark green leaves, was a pretty thing with orange
and black feathers. He whistled away as if he did not have a care in the
world.

And they did not have to be told--they knew who it was. It was their old
friend, the Oriole.

He didn't stay still very long ever, for he was a busy fellow. But once he
swung on a twig for a little while. They saw that he was almost as big as a
robin, with head and shoulders of black, the wings black too, and most of
his tail. But the rest of his body was like the prettiest orange-coloured
velvet they had ever seen. He was singing something like this:

"What a fine day, what a fine day.