It is like the friction of iron against iron without oil on the bearings.

This is the tree-climber calling to his mate.

He creeps over the boles of the birch, and where the larger limbs join the trunk, trailing his tail along the bark, and clinging so closely that but for the sharp note he would be passed.

Even when that has called attention, the colour of his back so little differs from the colour of bark that if he is some height up the tree it is not easy to detect him.
The days go on and the hedges become green--the sun shines, and the blackbirds whistle in the trees.

They leave the hedge, and mount into the elm or ash to deliver their song; then, after a pause, dive down again to the bushes.