Grinnell and Storer (1924) write:
The more intensive occupancy of the Yosemite Valley during recent years and the operations of the government employees in promptly removing dead but standing trees to be cut up for wood has operated to the detriment of the woodpeckers which seek such trees for nesting holes. So it was no surprise, in May, 1919, to find a number of telephone or electric power poles near Redwood Lane which had been prospected for nesting sites by woodpeckers—the California, to judge from the size of hole and general location. Dearth of suitable natural sites had forced the birds to at least investigate these newly established dead-tree substitutes. With no substitutes at all available, the only result to be logically looked for, as a result of man’s interference with the natural order of affairs, would be the disappearance of woodpeckers. The question arises here as to the justification of the administratiton in so altering natural conditions in National Parks as to threaten the persistence there of any of its native denizens.
Eggs.—The California woodpecker lays ordinarily four or five eggs; six eggs are not very rare; and as many as ten have been found in a nest, probably the product of two females. The eggs vary from short-ovate to elliptical-ovate. They are pure white, with very little or no gloss. The measurements of 52 eggs average 25.98 by 19.78 millimeters; the eggs showing the four extremes measure 29.9 by 19.0, 27.9 by 22.6, 22.0 by 18.6, and 24.38 by 18.29 millimeters.
Young.—The period of incubation is said to be about 14 days, in which both parents assist. Both also help to feed the young. Harriet Williams Myers (1915) made some interesting observations on a late brood of young California woodpeckers, which she found in a hole in a telephone pole, on September 11, between Los Angeles and Pasadena. She says:
In an hour’s watching the birds fed 28 times, the shortest interval being one-half minute, the longest eight. In nine minutes they fed eight times.
On the 15th of the month, when I believe the young must have been about ten days old, they were fed 24 times in 58 minutes. The food given them now was mostly acorns which the adults took from the nearby poles, sometimes digging them out in pieces, and sometimes taking them to the top of a flat pole where they pounded away for some minutes before coming to the nest with their bills stuffed full of the white bits. From this time until the young left the nest they were fed mostly on these acorns.
One of her most interesting observations was that an apparently young bird, presumably a fully grown member of an earlier brood, joined the two parents that were feeding the young in the nest. At one time, this immature bird entered the nest, while the parents were away, apparently for the purpose of being fed by them, and remained there for some time. Meanwhile—
when the adults came to feed they did not go inside but reached over, fed, and flew away. Three times one of them did this, but the fourth time, when the male came, he stood on one side of the hole and I heard him give low, guttural notes. * * * Presently, the truant young, for such he proved to be, appeared in the doorway and, with open mouth, begged for just one bite. * * * But the old bird was unrelenting and stayed in his position by the hole until the bird inside, which was undoubtedly a former nestling, came out and flew onto the wire above, when the adult male went within.
Just to prove that he was not all baby, the former nestling turned in and helped feed. Several times he went into the hole and came directly out, and I might have thought that he was in there in hopes of getting fed had I not distinctly seen a big fly in his bill as he entered. Each time as he bobbed into the hole several white bars showed plainly on the underside of the outer tail feathers. It was this marking of a young bird which convinced me that he was a former nestling. In every other respect he resembled a male California Woodpecker. Once more, during my watching, he slipped into the nest, staying eight minutes before they got him out. The first time it had been twenty minutes.
From the above, and from the observations of Frank A. Leach (1925), to be referred to later, it seems that the California woodpecker often, if not regularly, raises two or even three broods in a season.