CALIFORNIA WOODPECKER. Melanerpes formicivorus bairdi Ridgway

Field characters.—Of medium size for a woodpecker, near that of robin. Conspicuously pied with black and white; patch on wing showing conspicuously in flight, broad bar across forehead, rump, and belly, white; throat yellowish white; black of chest broken into streaks toward belly; conspicuous red patch on top of head; iris of eye white. (See pl. 5b). Sexes alike save that in female the red crown patch is smaller, being separated by a black interval from white bar on forehead. Movements typically wood pecker-like. Flight undulating to a degree; a short series of strong flaps, then a deep sweep on set wings. Voice: A nasal yá-kup, yá-kup, yá-kup; or krrá-ka, krrá-ka, the r's rolled.

Occurrence.—Most numerous in, and characteristic of, the Upper Sonoran Zone; present also down along the Merced River, following the bordering strips of valley oaks out into the Lower Sonoran San Joaquin Valley, as around Snelling; ranges upward locally into Transition Zone, the highest stations being near Coulterville, at 3500 feet, and near Columbia Rock, at 5200 feet, in Yosemite Valley. Apparently resident throughout the year wherever it occurs at all.

The California Woodpecker is emphatically an inhabitant of oaks, more so indeed than any other species. While foraging sporadically into cottonwoods and conifers, individuals may be almost always traced to headquarters among oak trees of one kind or another. This quercine attraction is evidently due to the bird's constitutional hankering for acorns as a staple article of diet. To tide over the annual period of famine in this particular food source, the California Woodpeckers show high development of the storing habit. In late summer and autumn their industry in gathering and snugly stowing away acorns according to their own peculiar method is perhaps second only to that of the Gray Squirrels. The results of this industry are well advertised, because of the birds' habit of ensconcing each acorn separately in a hole in the surface of a tree trunk, bored accurately to a size to fit. These acorn holes are close set over the surface of the bark, sometimes from within 2 feet of the ground to a height of 75 feet or more. The tree or trees selected by a pair of California Woodpeckers for storage purposes may not be of any species of oak at all. On the floor of Yosemite Valley, ancient, partly dead incense cedars more often, perhaps, than any other tree, show this woodpecker's work. When the acorns have been removed the trunk of the tree is left with a curious pitted appearance as if it had served repeatedly as a target for a large-bore rifle.

On November 5, 1915, along the road below the foot of Yosemite Falls Trail, an old woodpeckered, dead-topped cedar trunk was studied, with the following results (Grinnell, MS). The acorn pits began about 3 feet above the ground and extended to a height of about 45 feet. The circumferences of the trunk at these two limits were, respectively, 15 feet and 9 feet. The pits were pretty evenly distributed all around the trunk; from a series of measurements it was estimated that they averaged 5 inches apart, between centers, all over the surface. This would make 2360 pits on this one trunk. The pits averaged 20 millimeters in diameter by 30 in depth, so they were evidently planned (and doubtless used though now empty) for the fat acorns of the golden oak. This is of interest, as the oaks immediately about were black oaks, which bear much smaller nuts, the nearest golden oaks being about 200 yards away at the base of the talus to the north.

In one large living yellow pine near Camp Ahwahnee in Yosemite Valley which had been very closely pitted, especially on the north side of the trunk, it was estimated that there was an average of 30 acorn holes a square foot placed all the way from 3 to 40 feet above the ground, and that there was a total of 10,500 holes in this one tree! Only the outer layers of the bark were penetrated by the holes, so that no damage appeared to have been done to the growing wood of the tree. In fact, the regular scaling off of bark would probably eliminate the holes altogether within a few years were they not continually deepened or renewed by the birds.

As far as observation goes, only one acorn is carried by one bird at a time. We may well marvel at the ingenuity displayed in the excavation of the holes, always to a diameter to admit of but a tight fit. The holes, too, are just deep enough to bring the butt of the acorn flush with the bark surface—just about 'bill-deep' for this woodpecker. As a usual thing it is impossible to take out, with the fingers, an acorn from its pit, both because of the smooth, elusive surface of the nut and because of its having been forcibly wedged into its socket. There is a great range in the size of the acorns of different species of oaks, from the small slender ones of the interior live oak to the relatively huge ones of the golden oak. Acorns of all sizes are utilized by the birds in the different zones; so that, all in all, an astonishingly acute faculty of adaptation must be credited to the California Woodpecker.

Fig. 47. Head and tongue (a) of California Woodpecker, showing general structure of tongue with backward-pointing brush at tip (b) and long insertion of base of tongue (c) around back of skull. The muscular arrangement within the sheath enclosing the tongue permits the latter to be protruded (as shown in a) when the woodpecker is pulling a grub out of a recess in the wood. Natural size.

Near Pleasant Valley, fence posts were riddled with holes (fig. 48a), many of which, on May 28, 1915, contained acorns of the previous autumn's crop. Some of these were so loose as to be easily withdrawn, while others were wedged tight. All examined had been inserted point foremost. In some holes only open shells remained, as if the birds had eaten the meat from the nuts without removing them, by breaking them open at the base. Some of the nuts were wormy, probably not a particular misfortune to the birds provided they were not too late for either worm or mast.

Two stomachs of California Woodpeckers shot contained only pieces of shelled acorn, ants, and gravel. At El Portal, in December, a pair of California Woodpeckers was found to regularly visit the fresh, bleeding borings of a red-breasted sapsucker in a golden oak—evidently sponging on their industrious neighbor.

In Yosemite Valley, these woodpeckers were observed during all our visits, winter and summer, in seemingly unvarying though not large numbers. Some days, however, they were very quiet, and might easily be overlooked in one entire morning's census; at other times their nasal chatter sounded almost continually, especially from along the north side of the Valley from the Royal Arches west to below Rocky Point. Often a pair or more made excursions from tree to tree through the cottonwoods around Sentinel Meadow, where they occasionally exhibited the trait of flycatching common to several species of this family. Launching out from a prominent tree top with vigorous wing-beats to waylay a passing insect, they would return in a wide sweep to the starting point. It is not to be inferred from the acorn-storing habit dwelt upon above that insects form an unimportant element in the bird's food. On the contrary, like the other woodpeckers, the California Woodpecker does a great amount of bark foraging, though it does show a decided aversion to pitchy conifers.

Fig. 48. (a) Fence-post studded with acorns of blue oak, storage method of the California Woodpecker. Photographed near Pleasant Valley, February 27, 1916. (b) Lewis Woodpecker at nest site in stub of Jeffrey pine. Photographed at Walker Lake, June 26, 1916.

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.

Nest holes about 30 feet above the ground were noted in each of two long-dead and barkless yellow pine stubs standing at the foot of the valley wall back of Yosemite Falls Camp. Individual birds used these for roosting places at night in December, 1914, only one bird occupying each hole. Near Pleasant Valley, May 24, 1915, a nest hole 10 feet above the ground in the trunk of a blue oak held squealing young.

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 administration in so altering natural conditions in National Parks as to threaten the persistence there of any of its native denizens.