In fact, he seemed as much at home among the trees as on the ground; and Buck had memories of nights of vigil spent beneath trees wherein the hairy man roosted, holding on tightly as he slept.
And closely akin to the visions of the hairy man was the call still sounding in the depths of the forest.

It filled him with a great unrest and strange desires.

It caused him to feel a vague, sweet gladness, and he was aware of wild yearnings and stirrings for he knew not what.
Sometimes he pursued the call into the forest, looking for it as though it were a tangible thing, barking softly or defiantly, as the mood might dictate.

He would thrust his nose into the cool wood moss, or into the black soil where long grasses grew, and snort with joy at the fat earth smells; or he would crouch for hours, as if in concealment, behind fungus-covered trunks of fallen trees, wide-eyed and wide-eared to all that moved and sounded about him.

It might be, lying thus, that he hoped to surprise this call he could not understand.