Page:The British Warblers A History with Problems of Their Lives - 4 of 9.djvu/40

 by carrying being equally as effective, and, in fact, more often resorted to. Nevertheless, no one could watch the vigorous efforts of a bird vainly endeavouring to swallow a leaf too large to pass down its gullet without concluding that it was not due to any desire on its part to do so, but that its whole behaviour was congenital, and that the instinctive procedure being thus interrupted accounted for the extreme bewilderment its attitude denoted, for you may see it arrive at the nest, deliver the food to the young, pick up a leaf and attempt to swallow it, then drop it and yet again pick it up, finally after a pause flying away; in a few moments it returns again with food, delivers it to the young, and again goes through the same performance with the leaf.

In whatever way we may regard such an episode, the truth of which anyone can test for themselves, it cannot be denied that the fact of a member of an insectivorous species attempting to swallow a bramble leaf, and that by no means a small one, is significant.

From yet another point of view the experiment with the leaf is interesting. It shows—at least I am inclined to believe so—that the bird has no knowledge of the relation between the means employed and the end attained; and it is just such an incident as this that increases my doubt as to whether intelligent modification has been that factor in the evolution of instinct which it is so often claimed to have been, for if such a combination of activities as we are here discussing had arisen by this means, assuredly the intelligence ought not to be of so low a degree as would be incapable of distinguishing between a leaf and a membraneous sac of excrement.

I once witnessed a scene with a pair of these birds which was interesting. Finding one evening a nest, in which the young were just hatched, placed in such a position that it could be watched with little difficulty, I determined to remove some of the vegetation surrounding it at once, so that the parents might have ample time to become accustomed to the change by the following morning. This I did, and returned