IN THE SHETLANDS 77 
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, 
