"Soon after the arrival of these birds in Chuquerca," says Bonelli, "the task of incubation commences, and when the summer is over, both the old and young, actuated, as it were, by the same impulse, wend their way southward, to return again when the sun has once more gladdened the earth. The nest is a somewhat loose structure, outwardly composed of interlaced fibres, slight twigs, and moss, and frequently lined with soft hair, like that of the Viscacha (_Lagostomus tridactylus_), with the lower portion prolonged considerably below the bottom of the cup-shaped interior, which is about an inch and a half in diameter and an inch in depth; the total length of the nest averaging from two inches and a half to three inches. The little structure is placed in situations similar to those selected by the Spotted Flycatcher, namely, against the sides of the gully, supported or entirely sustained by any hanging root or twig that may be best adapted to afford it security; the part of the nest next the wall is much thicker, but of a coarser texture than the circular portions of the structure. The two eggs are oblong in form, of a pure white, and about half an inch in length. The difficulty of shooting these birds is inconceivably great, from the extraordinary turns they make when on the wing: at one instant darting headlong into a flower, at the next describing a circle in the air with such rapidity that the eye, unable to follow the movement, loses sight of it until it again returns to the flowers." * * * * * The MASKED HUMMING BIRDS (_Microrhamphi_) have a short, straight beak, moderately long and broad wings, and long, forked tail, which occasionally varies in its formation. The head and neck are adorned with peculiar tufts of feathers. THE SHARP-BEARDED MASKED HUMMING BIRD.