These birds, described somewhat ambiguously by certain authorities as Sea Ducks, for all the species are by no means exclusively marine, yet all are expert divers, form a fairly well-defined and homogenous group, or sub-family, termed by systematists, Fuligulinæ. They are characterised by having a pendant lobe, or membrane, attached to the hind toe, and by their anteriorly scutellated tarsi. All the Ducks in this sub-family habitually dive for their food, and their movements in the water are remarkably agile. The sexes generally present considerable difference in colour, the males, as usual, being the most handsome and conspicuous. The young are always hatched covered with down, and soon able to accompany their parents on the water. The females have a single moult in autumn, but the males a partially double one. Diving Ducks, in fact all species in the family, in first plumage, closely resemble the old female, and acquire the adult plumage after the first autumn moult. We will deal first with the resident species, as being constant features in the bird life of the coast and sea. EIDER DUCK. No Duck is more thoroughly attached to the sea than this species, the _Anas mollissima_ of Linnæus and Latham, but the _Somateria mollissima_ of most modern ornithologists. Unfortunately it is somewhat restricted in its distribution, only breeding in one locality on the English coast, occurring more or less accidentally elsewhere. Ireland is not even so fortunate, for no nesting station is known round the entire coastline of the island. The Eider Duck is a decidedly northern bird, and is found, if somewhat locally, round the coasts of Scotland, extending to the outlying islands, including St. Kilda, where I have taken its nest. To most people, perhaps, the down of the Eider Duck, in the form of a coverlet, is more familiar than the bird itself. Although somewhat clumsy in appearance, the male Eider is a singularly handsome and conspicuous bird—conspicuous, one might say, when standing on the rocks or paddling about the still water near the shore, but even in a very moderately rough sea the bird is detected with difficulty, especially at a distance, for the white crests and dark waves effectually harmonise with, and conceal, its striking piebald plumage. The two predominating colours of the male Eider are black and white, the latter occupying most of the upper surface, the former most of the lower; the head, however, is variously marked with black, white, and pale green. The female is dark chestnut-brown, variegated with brownish-black. The Eider Duck is so thoroughly sea-going in its habits, that it rarely even flies over the land, except to reach its nest, and will rather follow the windings of the coast than cross even a narrow headland. In our islands it is practically sedentary, only wandering south a little way during winter. Its favourite haunts are rocky islands and coasts, where bays and quiet