From the moorlands to the mountains and lochs is in many localities a transition of an almost imperceptible character. In not a few cases the moors terminate in mountain summits beyond the borderland, where the two species of heather cease to climb, or the most sturdy and tenacious ling that clothes the hillsides for still another thousand feet or more. In a similar manner the lochs are usually situated in hollows among the hills, or penetrate in winding fiords from the sea between towering highlands or heath-clothed wastes that at higher altitudes terminate in bare and wind-swept mountain summits. As with the avifauna of the moors and heaths we shall find that the birds of the mountains are more or less a shifting population. Indeed the similarity is made even more complete by the fact that in both regions--moor and mountain--we find but one sedentary species. Upon the moors we found the practically resident Red Grouse; upon the mountains we shall find the Ptarmigan, a bird that clings to the bleak summits throughout the year. In some respects the Ptarmigan is a more interesting species than the Red Grouse; there is more variety in its economy, and the bird itself is one of the most beautiful examples of protective coloration that the entire range of organic life can show. Our first acquaintance with the Ptarmigan was made nearly twenty years ago, near the summit of the Cuchullin Hills in Skye. Although the time was May, patches of snow were lying in the hollows and a cold piercing wind swept along the hillsides. Lower down the slopes we had lingered to watch the gambols of a pair of Ravens that were haunting the rocks; whilst a Peregrine Falcon had just swept by. Upon a small piece of level ground we flushed several Ptarmigan, one after the other, that had been lying concealed on the stony face of the mountain. They were readily identified by their white wings. After the first bird had risen we scanned the ground carefully for others, but none were seen until they rose in noisy flight and sped away. It is interesting to remark that the Peregrine we had seen a short time before must have flown right over the spot where these Ptarmigan were crouching. Possibly the recent appearance of the Falcon had made them lie closer than usual, and rendered them loth to take wing. With the exception of a few weeks in the very depth of winter, the Ptarmigan is more or less changing in colour throughout the year. In mid-winter, as most readers may know, the bird is pure unsullied white, with the exception of a jet-black patch in front of the eye in the male, and the outermost tail-feathers, which are black in both sexes. In early spring, sometimes it is said by the middle or end of February, the first signs of the coming summer plumage are seen on the neck, and during the three succeeding months the birds undergo a complete transformation, the feathers on the breast, it should be noted, being assumed last of all. It is a significant fact that the parts of the plumage least exposed, such as the flight feathers and the feathers on the belly, present the smallest amount of change from the white winter dress. This is more apparent in the male than in the female, doubtless owing to the fact that the latter is more liable to injury whilst brooding on the nest. Broadly speaking, in the male in summer plumage the upper parts and the breast and flanks are dark-brown, more or less mottled, and barred with gray and buff; whilst in the female the upper parts are darker, practically black, mottled with gray and rufous, and the under parts are chestnut-buff barred with dark-brown. This plumage prevails during June and July, although subject to some change by sun and abrasion, whilst towards the end of the latter month signs of the autumn livery begin to be apparent. In this dress again the sexes are similar, as we might naturally expect to be the case, now that the breeding season is over, and both male and female are exposed to the same conditions of life. The upper parts, the breast and flanks, are gray, vermiculated with black. By the end of August this autumn dress is fully attained. It is worn for nearly a couple of months, subject of course to some change from abrasion and sun. Then comes the transition to the white winter plumage, which in most cases becomes complete by the middle of November contemporaneously with the snow that lies upon the mountains for the next three months or more. This beautiful arrangement of nature becomes even more impressive by certain comparisons.