Plumages.—The young are hatched naked and blind, but the juvenal plumage is acquired before the young bird leaves the nest. In this plumage the young male closely resembles the adult male and the young female is much like the adult female in general color pattern, but the red of the crown and nape is duller and more or less mixed with dusky or black; sometimes the crown is nearly all black mixed with some scarlet feathers; the colors everywhere are duller, lacking in gloss, and the plumage is softer, less firm; the yellow of the throat is less pronounced; the streaks on the breast are less sharply defined; the tertials and scapulars are tipped with white, and there are narrow white tips on the two outer tail feathers on each side, but these tips wear away during winter, or sooner; there are at least two white spots on each web of the outer tail feather, which are in evidence all through the first year; as the juvenal wings and tail are retained until the next summer molt, birds of the year may be thus recognized; the bill is smaller and weaker than that of the adult. The molt of the juvenal contour plumage begins in August or September.
Adults have a complete annual molt between July and September, mainly in August.
Food.—Some prominent California ornithologists have named this bird the “California acorn-storing woodpecker,” a rather long but very appropriate name, for it designates one of its most characteristic habits and names the largest item in its food supply. W. L. Dawson (1923) has this to say on the subject:
From time immemorial this bird has riddled the bark of certain forest trees and stuffed the holes with acorns. Speculation is still rife as to the cause or occasion or necessity or purpose of this strange practice, but the fact is indisputable and the evidence of it widely diffused. * * *
What he accomplishes the photographs show well enough,—the close, methodical studding of bark or wood of any kind with acorns, chiefly those of live-oaks, over immense areas. The cultures, once started, are wrought upon continuously year by year, as material avails or the colony flourishes. Live-oaks themselves are the commonest hosts, together with the white, or post, oak, and the black oak of the southern counties. After these come sycamore and yellow pine or, more rarely, eucalyptus. Telegraph and telephone poles, gables, cornices, and, in fact, any wooden structure where they are permitted to work, if near the source of acorn supply, may come in for ornamentation. On a small square-sawed telephone pole near Marysville I found sixty acorns (and pecans purloined from a neighboring orchard) imbedded in a space five inches wide and two feet long. At that rate the pole carried some 1500 of these tiny storehouses.
In Tecolote Canyon, west of Santa Barbara, there is a giant sycamore which I count one of the handsomest examples of Carpintero’s workmanship—an unbroken shaft, at least forty feet high and three feet across the inlaid face, covered with a “solid” mass of acorns totalling, say, some 20,000. Strawberry Valley in the San Jacinto Mountains appears to be a paradise for the California Woodpecker. Here majestic oaks (Quercus californica) alternate with still more majestic pines (Pinus ponderosa), the former for sustenance and the latter for storage, and the doughty “California” is probably the most abundant bird in the valley. The boles of the most enormous pines are methodically riddled with their acorn-carrying niches, and in some of the trees the work is carried through from base to crown. In one such tree I estimated that there were imbedded no less than 50,000 acorns.
Dr. William E. Ritter has made an intensive study of this interesting habit of the California woodpecker and has published the results of his observations and theories in three extensive papers (1921, 1922, 1938). There is much food for thought in these scholarly papers, to which the reader is referred, but space here will permit only brief quotations from or references to them. As to whether the hole drilling is injurious to the trees, he says (1921): “Although I have examined many storage pines in widely separated localities, I have never seen anything even suggestive of harm to the trees from the holes. Never, so far as I have noticed, do the holes pierce through into the deeper living layers of the bark.” He noticed that “almost without exception the nuts were inserted tip in and base out, most of them fitting the hole snugly,” having been driven in good and hard, and flush with the surface of the bark, or even countersunken below it; and that “to a certain extent the store holes are made to fit the size of the acorns they are to receive”; this latter point was discovered when he noted that, in a region where the black oak (Quercus kelloggii) predominated, the holes were considerably larger than they were in the live-oak region, the acorns of the black oak being sharply larger than those of the live oak. In some cases the acorns were not driven in flush with the bark, the base being left protruding somewhat and thus leaving them vulnerable to pilfering by rodents and perhaps some birds; in this connection, he says: “Conclusive evidence that nut-eating rodents (squirrels, rats) prey upon the acorns stored by the woodpeckers was first obtained on the present visit. Two trees were found on which the bark immediately around acorn holes had been gnawed by rodents, as unmistakably proved by the tooth marks. The acorns were gone from some of these holes, but not from all, thus showing that the marauders had failed in some of their efforts.”
Summarizing his first paper, he makes the following statements:
As to hole drilling: While the holes are made expressly for the reception of acorns, many holes are probably made which are never used, holes are made at seasons of the year when there are no acorns to store, and large numbers of perfectly serviceable holes seem to be abandoned even in localities where both birds and acorns are abundant, and new holes are being made.
As to the storing business itself: While this is of distinct service to the food necessities of the woodpeckers, the instinct sometimes goes wrong to the extent of storing pebbles instead of acorns, thus defeating entirely the purpose of the instinct. Again, large numbers of acorns are sometimes stored, the use of which is so long delayed that the acorns become wholly or largely unfit for food, and this in places where the bird population seems normal. Finally, acorns are sometimes stored in such fashion as to make them easy prey for marauding rodents, when with some definite foresight and a little more work such exposure could easily be largely avoided.