But we have encountered one truth which must always be held in mind in science—that a theory is not proved while a single fact remains rebellious and unsubdued. We might have examined every other woodpecker in the continent but just one; we might have seen that every other one agreed with our theory, as it does; we might have supposed that the explanation was good past doubting; but that one exception—if it was a logcock—would still over-turn the whole theory; and the very facts that we relied upon to strengthen us—its resemblance in size, habits, shape, and color to the ivory-billed woodpecker—have been the strongest possible means of totally demolishing our fine theory. We have learned, if nothing more, that all the facts must be examined and accounted for before an explanation is accepted as indisputable.
XIII
THE WOODPECKER’S TOOLS: HIS TAIL
If we study the woodpecker’s anatomy and observe his broad, strong, highly-arched hip-bones and the heavy, triangular “ploughshare” bone in which the tail feathers are planted, as well as the stiffness and strength of the tail itself, we must conclude that it is not by accident that he uses his tail as a prop. The whole structure shows that the bird was intended “to lean on his tail.” What we wish to discover is how good a tail it is to lean on.
Tail of Hairy Woodpecker.
Our first impression is that the woodpecker’s tail might be improved. Why are not the tips of the feathers stiffer? Why is it so rounded? Most of the work seems to fall on the middle feathers, and in some species, as the downy and the hairy woodpeckers, these end in decurved tips so soft and unresisting that they seem quite unfit to give any support. Would it not be better if the woodpecker’s tail had been cut square across and made of feathers equally rigid and ending in short stiff spines? For we see that the woodpecker’s tail is not only weak in its inner feathers, but weaker still in its outer ones, and it is stiff, in most species, only in the upper three fourths of its length.
When we propose a change in nature it is wise to inquire whether our improvement has not been tried before and to learn how it worked. How many kinds of birds have we that use their tails for a support? What are their habits and what sort of tails have they?
