The migrating wild creatures, whether birds or beasts, always arrest the attention. They seem to link up animal life with the great currents of the globe. It is moving day on a continental scale. It is the call of the primal instinct to increase and multiply, suddenly setting in motion whole tribes and races. The first phoebe-bird, the first song sparrow, the first robin or bluebird in March or early April, is like the first ripple of the rising tide on the shore.