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Rh left at the point of detachment of the old nail is quite a useful indication of age in cases where there is a doubt as to a bird being over twelve months old or of the year. The presence of the groove showing that the claws have once at least been shed is conclusive proof that the bird is more than twelve months old.

In June there is another characteristic appearance in the hens, namely the bare patch of abdominal skin which results from the shedding of the abdominal feathers, grown in the previous September. The loss of these feathers leaves a naked patch of skin on the abdomen of a hen that has been sitting, and this patch remains naked for the next few months (Pl. .). The general character of a June hen in health is that of the completed summer-nesting plumage, broad-barred buff and black over all the upper and under parts, excepting the abdominal area, the lower breast, wings, and tail. But it looks already somewhat faded and worn; and it is quite probable that in acquiring so perfect a plumage for sitting unnoticed on a nest built amongst the heather, the economic absence of the redder pigment in the feathers is in part a result of the acknowledged fact that for longer and more trying use, and for wear and tear in feathers, darker pigments are required, whereas for the short-lived and less exacting requirements of the summer plumage in the hen Grouse from April to June the buff and black feathers, with very much poorer wearing qualities, are found to be sufficient. The accompanying figures of a few worn-out and moulting feathers taken from a hen in summer plumage, show how distinctly better the black pigmented parts of the feather stand wear and tear than the yellow parts (Pl. ). Certain pigments have a value, therefore, of a very practical nature apart altogether from the aesthetic point of view of attractiveness, or the rather hypothetical view of assimilation to surroundings for purposes of safety or to assist in obtaining food. He would be unwise, however, who denied that all three factors play a part in the very beautiful nesting plumage of the hen Grouse.

It very occasionally happens that the hen Grouse, instead of retaining the redder plumage of the previous autumn's growth on the abdomen until it drops off during incubation, grows an almost universal spring plumage of buff and black broad-barred feathers covering the lower breast and abdomen as well as the remainder of the body from head to tail. A skin showing this condition is preserved in the National Collection, and there is an almost equally perfect specimen in the Committee's Collection, No. 919.