On the Acorn-Storing Habit of Certain Woodpeckers
On the Acorn-storing Habit of Certain Woodpeckers
In a recent article in the CONDOR, Dr. William E. Ritter gives an interesting discussion of the habit of the California Woodpecker of inserting acorns and sometimes pebbles into small holes drilled for their reception in the bark and dead wood of trees. During a two years stay in British Honduras the writer had a good opportunity to observe this same curious instinct in a closely related form, Meianerpes formicivorusc albeolus. These extremely industrious birds not only store acorns in the same manner as the California Woodpecker, but also deposit them in great quantities in hollow trees and similar places. I have seen a hollow pine tree with a cavity six to eight inches in diameter filled for a distance of nearly twenty feet with acorns dropped into a good sized hole at that distance above the ground. Acorn-filled trees of this sort I found not uncommon. Sometimes an opening at the bottom showed the earlier acorns deposited, completely decayed and crumbling to dust. They must have been there for several years, and probably were not brought by the same birds that completed the accumulation. I often saw the woodpeckers bring the acorns and drop them into these “acornaries”.
I lived for some time in an old house in which the roof of an upper veranda had been supported by timbers six inches square. These had been injured by termites and rendered unsafe, and had then been boxed with heavy boards of the proper width. Later the termites had completed their work of destruction and had almost entirely removed the timbers, leaving the hollow boxing. The woodpeckers had made holes near the tops of some of these and used them for acorn storage. One that I noted was filled for a distance of at least four feet, as could be seen where the boards had sprung apart slightly, and possibly much farther.
In these cases it wouid be utterly impossible for the birds ever to make use of the acorns in any way, yet they go on generation after generation laboriously gathering them. Furthermore, in an even, tropical climate like that of British Honduras, where there can be but little variation in food supply from season to season, it is difficult to see how, under any circumstances, such a habit could be of any great advantage; but even granting that it is so in cases where the accumulation is accessible, these instances show how an over-delevoped instinct may lead to actions not only useless but highly absurd.
So far as the California Woodpecker is concerned, Dr. Ritter's conclusions are in all probability correct. This suggests the possibility that the Central American bird was derived-from the more northerly form or from northern ancestry, which acquired the instinct under conditions like those now existing in California, and that, as it pushed gradually into the tropics, it retained the instinct long after it had ceased to be of any utility. Such speculations, however, are of doubtful value.
Morton E. Peck
Willamette University, Salem, Oregon, July 8, 1921
