Page:BirdWatcherShetlands.djvu/98

78 irrespective of anything that may be growing upon it. Having seen them do both, I see no reason why I should reject the evidence of my eyesight in the one case more than in the other. What interests me is that I have several times during this week seen the same duck, with her young ones, feeding along this one flat part of the coast-line, where it forms a beach, whereas all the others that I have seen have kept in the neighbourhood of the rocks. Even about the shores of this small island it seems as though a process of differentiation were going on, and that whilst the great majority of the eider-ducks affect a diet of shell-fish, and, therefore, haunt the broken, rocky parts where it is to be best obtained, some few prefer the seaweed growing on the smooth, shallow bottoms, which they therefore do not leave, or, at least, more frequently resort to.

A difference of food like this, involving a residence in different localities, must lead to change in other habits, to which structure would, in time, respond, so that, at last, upon Darwinian principles, two different birds would be produced. Thus anywhere and everywhere one may see with one's own eyes—or think that one sees, which is just as instructive—the early unregarded stages of some important evolutionary process.

It is a good thing, I think, thus to exercise one's imagination, and by observing this or that more or less slight deviation from the main stream of an animal's habits, to try and picture its remote future descendants.