I surmise, what it is that gives this black, or rather indigo, tinting to the rock, and in trying to get nearer, the mother duck is again alarmed, and with another deep "quorl" or two, runs quickly down the slant, and slides into the water, close followed by her two little children. This time she swims away with them and returns no more, leaving me as disappointed as though I had thirsted for her blood.
Going down now to the rocks, where they have just been, I find that the black appearance of which I have spoken is caused by immense numbers of quite small mussels which grow thickly wedged together. It is on these that all three have been feeding, and I have no doubt that they form one of the staples of the eider-duck's food just now. Earlier in the year it seemed to be all diving, and when they brought anything up it did not look like a mussel. All about the rocks there are certain little collections of broken mussel-shells—often of a very pretty violet tint—coagulated more or less firmly together, and these must evidently have been ejected, as indigestible, by birds that had swallowed them; but whether by gulls only, or by both gulls and eider-ducks, I cannot tell. Gulls, I know, disgorge these queer kinds of pellets as well as others still more peculiar, since they occur over the interior of the island in numbers too great for any other bird to have produced them.
The eider-ducks, therefore, feed on the beds of mussels that the sea exposes at low tide, but they also, to go by appearances, devour the actual seaweed,
