these birds should avoid the copsy swamps near Moraine Lake, and yet select for breeding homes the valleys both above and below it. Perhaps the valley of Moraine Lake is a little too secluded and shut in by the towering mountains on three sides, the other places being more open and sunshiny. The upper valley was the summer home of that musician _par excellence_ of the Rockies, the green-tailed towhee, and he sang most divinely, pouring out his "full heart In profuse strains of unpremeditated art." Having elsewhere described his minstrelsy and habits with more or less fulness, I need give him only this passing reference here. A little bird with which I here first made acquaintance was an elegant species known as Audubon's warbler, which may be regarded as the western representative of the myrtle warbler of the East. The two birds are almost counterparts. Indeed, at first I mistook the Audubon for the myrtle. The former has a yellow throat, while the latter's throat is white. In all the upper mountain valleys, and on the steep slopes of the western as well as the eastern side of the Divide, I had the Audubon warblers often at my elbow. In summer they make their homes at an altitude of seven to eleven thousand feet, and are partial to pine timber; indeed, I think I never found them elsewhere, save occasionally among the quaking asps. I learned to distinguish Audubon's chanson from those of his fellow-minstrels. It is not much of a song--a rather weak little trill, with a kind of drawl in the vocalization that forms its diagnostic feature. The persistency with which it is repeated on the solitary pine-clad mountain sides constitutes its principal charm. The winter haunts of Audubon's warblers are farther south than Colorado, mostly in Mexico and Guatemala, although a few of them remain in the sheltered mountain valleys of the western part of the United States. Early in May they appear on the plains of eastern Colorado, where they are known only as migrants. Here a double movement presently takes place--what might be called a longitudinal and a vertical migration--one division of the warbler army sweeping north to their breeding grounds in Canada, and the other wheeling westward and ascending to the alpine heights among the mountains, where they find the subartic conditions that are congenial to their natures without travelling so great a distance. Here they build their nests in the pine or spruce trees, rear their families, and as autumn approaches, descend to the plains, tarry there a week or two, then hie to their winter homes in the South.