This is, of course, a very general statement and is subject to endless exceptions. The finches that, when transported to Australia from England, changed the style of their nests radically and now build in a fashion entirely different from that of their parents; the little goldfinch of New England that will build a false bottom to her nest to cover up the egg of a cow-bird that has been left to hatch among her own; the grouse that near the dwellings of men are so much wilder and keener than their brethren of the wilderness; the swallows that adopt the chimneys and barns of civilization instead of the hollow trees and clay banks of their native woods,—all these and a score of others show how readily instinct is modified among the birds, and how the young are taught a wisdom that their forefathers never knew. Nevertheless it is true, I think, that instincts are generally sharper with them than with animals, and the following cases suggest all the more strongly that we must look beyond instinct to training and individual discovery to account for many things among the feathered folk.
The most wonderful bit of bird surgery that has ever come to my attention is that of the woodcock that set his broken leg in a clay cast, as related in a previous chapter; but there is one other almost as remarkable that opens up a question that is even harder to answer. One day in the early spring I saw two eider-ducks swimming about the Hummock Pond on the island of Nantucket. The keen-eyed critic will interfere here and say I was mistaken; for eiders are salt-water ducks that haunt only the open sea and are supposed never to enter fresh water, not even to breed. That is what I also supposed until I saw these two; so I sat down to watch a while and find out, if possible, what had caused them to change their habits. At this time of year the birds are almost invariably found in pairs, and sometimes a flock a hundred yards long will pass you, flying close to the water and sweeping around the point where you are watching, first a pretty brown female and then a gorgeous black-and-white drake just behind her, alternating with perfect regularity, female and male, throughout the whole length of the long line. The two birds before me, however, were both females; and that was another reason for watching them instead of the hundreds of other ducks, coots and sheldrakes and broadbills that were scattered all over the big pond.
The first thing noticed was that the birds were acting queerly, dipping their heads under water and keeping them there for a full minute or more at a time. That was also curious, for the water under them was too deep for feeding, and the eiders prefer to wait till the tide falls and then gather the exposed shellfish from the rocks, rather than to dive after them like a coot. Darkness came on speedily to hide the birds, who were still dipping their heads as if bewitched, and I went away no wiser for my watching.
A few weeks later there was another eider, a big drake, in the same pond, behaving in the same queer way. Thinking perhaps that this was a wounded bird that had gone crazy from a shot in the head, I pushed out after him in an old tub of a boat; but he took wing at my approach, like any other duck, and after a vigorous flight lit farther down the pond and plunged his head under water again. Thoroughly curious now, I went on a still hunt after the stranger, and after much difficulty succeeded in shooting him from the end of a bushy point. The only unusual thing about him was that a large mussel, such as grow on the rocks in salt water, had closed his shells firmly on the bird's tongue in such a way that he could neither be crushed by the bird's bill nor scratched off by the bird's foot. I pulled the mussel off, put it in my pocket, and went home more mystified than before.
That night I hunted up an old fisherman, who had a big store of information in his head about all kinds of wild things, and asked him if he had ever seen a shoal-duck in fresh water. "Once or twice," he said; "they kept dipping their heads under water, kinder crazy like." But he had no explanation to offer until I showed him the mussel that I had found on the duck's tongue. Then his face lightened. "Mussels of that kind won't live in fresh water," he declared at a glance; and then the explanation of the birds' queer actions flashed into both our heads at once: the eiders were simply drowning the mussels in order to make them loosen their grip and release the captive tongues.
This is undoubtedly the true explanation, as I made sure by testing the mussels in fresh water and by watching the birds more closely at their feeding. All winter they may be found along our coasts, where they feed on the small shellfish that cover the ledges. As the tide goes down they swim in from the shoals, where they rest in scattered flocks, and chip the mussels from the ledges, swallowing them shells and all. A score of times I have hidden among the rocks of the jetty with a few wooden decoys in front of me, and watched the eiders come in to feed. They would approach the decoys rapidly, lifting their wings repeatedly as a kind of salutation; then, angered apparently that they were not welcomed by the same signal of uplifted wings, they would swim up to the wooden frauds and peck them savagely here and there, and then leave them in disgust and scatter among the rocks at my feet, paying little attention to me as long as I kept perfectly still. For they are much tamer than other wild ducks, and are, unfortunately, slow to believe that man is their enemy.
I noticed another curious thing while watching them and hoping that by some chance I might see one caught by a mussel. When a flock was passing high overhead, any sudden noise—a shout, or the near report of a gun—would make the whole flock swoop down like a flash close to the water. Plover have the same habit when they first arrive from Labrador, but I have hunted in vain for any satisfactory explanation of the thing.
As the birds feed a mussel will sometimes close his shells hard on some careless duck's tongue or bill in such a way that he cannot be crushed or swallowed or broken against the rocks. In that case the bird, if he knows the secret, will fly to fresh water and drown his tormentor. Whether all the ducks have this wisdom, or whether it is confined to a few rare birds, there is no present means of knowing. I have seen three different eiders practice this bit of surgery myself, and have heard of at least a dozen more, all of the same species, that were seen in fresh ponds or rivers, dipping their heads under water repeatedly. In either case two interesting questions suggest themselves: first, How did a bird whose whole life from birth to death is spent on the sea first learn that certain mussels will drown in fresh water? and, second, How do the other birds know it now, when the need arises unexpectedly?
