For a few weeks longer the four babies scrambled about the doorway and looked longingly out at the wonderful green tree-world. They did not dare to step out upon the slender branches, for fear of falling off. It made them feel dizzy to look away down to the ground below. They did not know how to cling to the limbs with their feet while they balanced themselves with their tails.

When the young squirrels were almost strong enough to learn to run and climb in the tree, the mother began to build an airier home higher up the trunk. The old nest was growing too warm for comfort, as summer brought the long sunny hours. The squirrel father was not there to help his mate. She had driven him away before the babies came. She thought the tree belonged to her, and that she needed all the room in the hollow for her little ones. She chased him off to live in the woods with all the other squirrel fathers till the babies were big enough to take care of themselves.

The mother squirrel worked on the new nest in the early morning. She bit off leafy twigs and carried them to the top of the tree. There, where two branches forked, she packed the sticks and leaves together in a loose ball. Then she pushed a doorway through, at one side or another, just as she happened to be standing. This was not such a neat home as one in the next tree. That other mother squirrel built her new nest of strips of bark tied together with ribbons of soft fibre. Over the doorway she hung a curtain of bark, and lifted it up carefully whenever she went inside.

At last the new home was ready. The old mother hurried down to the hollow and called the babies to come out and follow her. They stepped out, one after another, just as carefully as they could. The smallest baby came last. He dug his claws into the bark and hung on. The branch seemed so narrow that he trembled from fear of falling. The tree swayed in the wind. The branch bounced up and down, and a leaf blew in his face. The poor little fellow shut his eyes, because everything seemed to be whirling round and round.

When he opened his eyes again he saw the three other little ones climbing up the trunk above him. They clutched the bark with their claws and moved forward, one paw at a time. The mother was running on ahead of them. Every few steps she turned around to coax them on faster.

Finally they reached a narrow branch which led over to the new nest. They crawled out on it, lifting one foot and then setting it down before lifting another. The farther they crept the narrower the branch grew under them. Their little paws began to slip over the smoother bark. The one in front tried to turn around, but he was afraid of losing his balance. So they all three scrambled backwards to the safe trunk.

The mother ran back to them, and chattered and scolded. Again and again they started out over the branch, and then went scrambling back. When at last the mother had coaxed them across to the nest she looked around for the smallest baby. There he was away down at the door of the old nest. The old squirrel was tired out. Her fur was ruffled and her ears drooped. She ran down to the nest and began to scold the little fellow. He sat up and put his paws around her neck, as if he were begging her to let him stay there. But she started him up the trunk and pushed him along to the branch. Then she took hold of him by the neck and carried him across to the new home.

After that the little ones were taken out every morning to practise climbing. Little by little they learned to balance themselves on the branches. Their tails were fluffy enough by this time to be of use in balancing. First to one side, then to the other, each baby tilted his tail as he crept along, step by step. Every day they could move a little faster. Finally they were able to chase one another up and down, from branch to branch. They went running around the trunks, skipping and leaping from slender twig to twig, and jumping from one tree to another, even through the air.

Sometimes one or another missed his footing after a reckless jump. Often he caught hold of a branch below by a single toe and lifted himself up to a firmer foothold. Or if there was no branch within reach, he spread out his fur, and flattened his tail, and went sailing down to the ground, almost as if he could fly. They never seemed to get hurt.