In his second paper (1922), after further observations, he states[1]:
My previous surmise that the birds are more interested in the grubs contained in the acorns than in the acorn meats has not been substantiated. What I could make out while in camp among them, by watching them gather and eat their breakfasts, was to the effect that good uninhabited acorns were chiefly used. Again and again birds were seen to pick nuts from the top-most branches of the black oak, fly with them in their beaks to some approximately horizontal surface of a large limb on a pine or another oak, make the surface aid them somehow (I never could see exactly how, as the “breakfast tables” were, of course, all on the upper surfaces of the limbs, and too high for my vision) in breaking and tearing open the nuts. Apparently cracks and chinks in the table top serve as holders for the acorns while they are being opened and eaten. This is indicated by the fact that dead and partly decayed trees or parts of trees were mostly used. I saw no indication of the feet being used in handling the nuts. The litter on the ground under the dining trees, consisting of shell fragments and lost bits of meat, indicated grubless nuts almost entirely. This result as to the use of mast is in agreement with Beal’s examination of the stomach contents of our woodpecker.
Charles W. Michael (1926), in the Yosemite Valley, made the interesting discovery that the California woodpecker has been known to learn by experience and to show some intelligence in its acorn storing. For a number of years when acorns were abundant no extensive storing was done, yet the woodpeckers lived in the valley all winter. Then came a lean year, with no acorn crop, when no storing could be done; and that winter the woodpeckers were forced to leave the valley for lack of food. The following year there was a bountiful crop of acorns, and the woodpeckers, having learned by experience, were busy filling up their storehouses. “From the above observations,” he says, “one might conclude that an abundance of acorns is not directly responsible for prodigious storing. In a land of plenty the necessity of laying aside stores for future consumption is obviated. It is the barren years that teach the value of thrift. Intelligence plus experience may well have been the cause of the excessive storing of this year. A few of the more intelligent woodpeckers that were forced last winter to abandon the valley for lack of food are now preparing against the next lean year.”
Claude Gignoux (1921) reports finding almonds stored in the bark of an oak tree on a ranch near Marysville, Calif., as well as in the side of a barn.
Dawson (1923) says: “A regrettable taste for fruit is occasionally cultivated, but this has not reached economic proportions, save in the case of almonds. Almond orchards thrive best at a very considerable distance from oak groves.”
Although acorns, almonds, walnuts, and pecans constitute nearly 53 percent of its food, and much more than that in fall and winter, the California woodpecker eats quite a variety of other food at different seasons. Prof. F. E. L. Beal (1910) examined the contents of 75 stomachs, which contained “22.43 percent of animal matter to 77.57 percent of vegetable.” Bendire (1895) says: “During the spring and summer its food consists, to a great extent, of insects, including grasshoppers, ants, beetles, and different species of flies, varied occasionally with fruit, such as cherries, which are carried off whole, apples, figs, and also berries and green corn.”
Mr. Skinner says in his notes: “At times this bird feeds very much like an eastern red-headed woodpecker. On May 9, 1933, one was seen on the trunk of an oak, only 4 feet above ground, making flycatcherlike sallies up under the foliage of the oak. And many times thereafter I saw the birds operating similarly within the foliage itself. In some instances I have seen these woodpeckers dart out from high up in tall yellow pines after passing insects, then gliding back on set wings. Sometimes they do this from tall electric poles, at times going out as much as 50 feet. Since there was every reason to suppose that the bird saw the insect before it started, this speaks well for its keenness of eyesight. At times, these woodpeckers glean insects from the bark of trees. In July, in the Yosemite Valley, hunting the twigs and bark for insects seemed the favorite method of getting food.”
Dr. Joseph Grinnell (1908) saw one of these woodpeckers, in the San Bernardino Mountains, drive a sapsucker away from its borings in an alder and then go “the rounds of the borings” drinking from each. Dr. Harold C. Bryant (1921) saw a California woodpecker robbing a nest of a pair of western wood pewees; he was “calmly perched on the pewee’s nest and eating one of the eggs. I could see the white and the yolk of the egg on the woodpecker’s bill, as he raised his head. After watching for some time, I attempted to frighten the robber away, but experienced considerable difficulty in doing so. When he finally left the nest the pewees continued to dart at him, to drive him farther away. Soon one of the pewees, apparently the female, returned to the nest, picked up an eggshell and flew off with it. I was unable to see what she did with it. In half a minute she returned and began incubating the remaining eggs.”
Behavior.—The California woodpecker flies in true woodpecker fashion, an undulating flight, interspersed with long dips during which the wings are partly closed and somewhat pressed against the sides of the body; during the rises the wings are flapped, displaying the black and white markings conspicuously; there is an upward sweep before alighting. Grinnell and Storer (1924) say: “When alighting on a tree trunk, these birds assume a vertical posture, head out, tail appressed to the bark. They move up by a hitching process—head in, tail out; up; tail in, head out. If a bird perches on a small horizontal branch, his position is more likely to be diagonal than directly crosswise. If a bird alights on the square top of a fence post, he seems ill at ease and soon backs over the edge into a more woodpecker-like posture.”
Mr. Dawson (1923) writes: “A most characteristic flight-movement is an exaggerated fluttering wherein progress is at a minimum and exercise at a maximum. In this way, also, they ascend at acute angles, sometimes almost vertically. With this movement alternates much sailing with outspread wings, and certain tragic pauses wherein the wings are quite folded.” A similar flight is thus described by Grinnell, Dixon, and Linsdale (1930) as follows: “Individual woodpeckers were often seen making a kind of flight the object of which we did not determine. A bird would fly in a nearly vertical direction from its perch for three meters or more and then commence an irregular swooping flight, finally coming back to the original perch.”