It must destroy immense numbers of Scolytidae, whose larvae tunnel the bark so extensively, and of other insects that crawl beneath the scales of bark for shelter during winter. I have several times imitated the work of this bird by prying off the successive layers of bark, and have been astonished at the great numbers of insects, and especially of spiders, so exposed.
Prof. F. E. L. Beal (1911) examined only 14 stomachs, but says that “half of the animal food of the white-headed woodpecker (Xenopicus albolarvatus) is ants, but the most pronounced characteristic of this bird is its fondness for the seeds of pines, which constitute more than half of the food.”
Grinnell and Storer (1924) say: “Stomachs of two adult birds, obtained at Merced Grove Big Trees on June 10, 1915, and at East Fork of Indian Cañon, June 24, 1915, both held ants, some of which were large carpenter ants. The stomach of one of the young birds from the nest mentioned above contained remains of 2 large spiders, a large ant, 2 boring beetles, and a whole fly larva.”
Major Bendire (1895) quotes Rollo H. Beck as saying: “I noticed one of these birds on some fallen logs near the road, busily engaged in catching spiders, searching for grubs, and frequently flying after passing insects, catching them in mid-air in the manner of the California Woodpecker.”
Behavior.—Dr. Merrill (1888) writes: “Though not shy, and with care generally approachable to within a short distance, it is watchful and suspicious, and seems to know very well what is going on even if it does not see fit to fly away, though it is more apt to do this than to dodge around the trunk. The flight is direct, and rather slow and heavy.” Dr. Merrill noted that the skull of the white-headed woodpecker is “noticeably less hard and dense” than the skulls of other woodpeckers; this is probably due to the fact that its method of feeding requires less heavy drilling into hard wood.
Mrs. Florence M. Bailey (1902) says: “Xenopicus works with apparent indifference on trunks or branches. Like the Nuttall woodpecker he often lights upside down. In hunting over the bark he easily backs down the trunk, or if he takes the notion will fly, or perhaps drop backwards, a foot or so. He will also light sidewise on a branch and grasp the limb with his tail as if afraid of falling off. It is interesting to see him explore cracks in the bark. Standing on the edge he pokes his head into the dark cavern, turning it from one side to the other inquiringly.”
Grinnell and Storer (1924) write:
At Tamarack Flat, on May 26, 1919, a female white-headed woodpecker was seen to flush from her nest about ten feet above ground in a dead pine stub. Tapping by one of us on a nearby hole had caused her to leave, but she returned to the vicinity almost immediately. Then, for fully 25 minutes, while the observer remained within watching distance the bird foraged, preened, and flew about from one to another of the circle of 8 or 10 trees within a 50-foot radius of the nest, but always kept the nest tree in her sight. About every 5 minutes she would fly to the nest. In approaching it, she would swoop below its level and then glide up to the site with decreasing speed so as to end her flight with little or no momentum. Then, having gained claw-hold, she would poke the fore part of her body into the hole, withdraw it at once and repeat this performance four or five times before flying away again. Finally, after fully half an hour had elapsed, and her suspicions had been allayed, she went in, to remain. During this entire time the male kept out of sight and was heard only twice.
Van Rossem and Pierce (1915) noted its manner of drinking, thus: “White-headed woodpeckers were often observed to drink at a small stream near our camp at Bear Lake, where a pine sapling grew from the edge of a small pool. On this sapling the birds would alight, usually about three feet from the base, ‘hitch’ quickly backwards down the trunk to the water, and, leaning sharply to one side, drink by quick, nervous dips.”
Another method of drinking is described by Grinnell, Dixon, and Linsdale (1930), as follows: “In mid-afternoon one flew down from a yellow pine to some shallow, running water in an open roadside near Mineral. It alighted in a horizontal position on the ground and dipped its bill into the water six times. After each dip the bird raised its bill skyward at an angle of fully eighty degrees from the horizontal. After drinking, the bird flew to a prostrate log, and foraged horizontally along its lower curvature.”