Charles W. Michael (1935) watched a nest containing young, in the Yosemite region, of which he says:
When we arrived, about ten o’clock, both parent birds were bringing food. We watched the birds for an hour and a half and in this period of time the male made nine trips to the nest hole and the female made seven trips. The young were small, as the parent birds went completely into the nest hole. The birds, male and female, always came onto the tree trunk above the nest hole and hitched jerkily downward until on a level with the hole. They landed anywhere between five and fifteen feet above the hole; the female was likely to land nearest to the hole. * * * About every other trip excrement was carried from the nest. When the male cleaned nest he carried the feces away and dropped them some distance from the nest. When the female cleaned nest she came to the entrance from within, looked about and then dropped the refuse before leaving the nest hole.
Plumages.—The most remarkable characteristic of this woodpecker is the striking difference in the plumages of the two sexes at all ages, from the first plumage of the young bird to its maturity; in most birds the sexes are much alike in the juvenal plumage; but the young male Williamson’s sapsucker is much like the adult male, and the young female is much like the adult female; the principal character common to both sexes at all ages is the white rump.
These young sapsuckers are fully fledged before they leave the nest.
The young male, in juvenal plumage in summer, differs from the adult male in having a smaller and weaker bill and softer, more blended plumage; the black areas, except the wings and tail, which are like those of the adult, are dull brownish black, instead of clear glossy black; there are usually numerous elongated white spots or streaks, more or less concealed, on the scapulars and upper back, and often a few small whitish spots on the crown; the chin and upper throat are white, instead of scarlet; the center of the breast and abdomen is dull yellowish white, instead of bright “lemon-chrome”; the sides and flanks are barred, instead of striped or spotted, with dusky.
The young female differs from the adult female in having a smaller and weaker bill and softer plumage; the black breast patch is entirely lacking; the breast, sides, and flanks are barred with dusky, but less distinctly than in the adult; and the yellow of the central breast and abdomen is much paler.
These two juvenal plumages are worn for only a short time in summer. I have seen young males molting into their first winter plumage, which is practically adult, as early as August 9; and young females begin to show the increasing black breast patch as early as August 6; but this molt is slow, or variable, and is sometimes not completed until November or December.
Adults apparently have their complete annual molt mainly in August and September.
Food.—Mrs. Florence M. Bailey (1928) says: “In 17 stomachs examined, 87 percent was animal matter and 13 percent vegetable. Of the animal contents, 86 percent was ants, and cambium made up 12.55 percent of the total food.”
Grinnell and Storer (1924) write: