Page:Territory in Bird Life by Henry Eliot Howard (London, John Murray edition).djvu/42



who have studied bird life throughout the year are aware that the distribution of individuals changes with the changing seasons. During autumn and winter, food is not so plentiful and can only be found in certain places, and so, partly by force of circumstances and partly on account of the gregarious instinct which then comes into functional activity, different individuals are drawn together and form flocks of greater or less dimensions, which come and go according to the prevailing climatic conditions. But with the advent of spring a change comes over the scene: flocks disperse, family parties break up, summer migrants begin to arrive, and the hedgerows and plantations are suddenly quickened into life. The silence of the winter is broken by an outburst of song from the throats of many different species, and individuals appear in their old haunts and vie with one another in advertising their presence by the aid of whatever vocal powers they happen to possess—the Woodpecker utters its monotonous call from the accustomed oak; the