Bent Life History of the Acorn Woodpecker
Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.
Bent Life History for the Acorn Woodpecker - the common name and sub-species reflect the nomenclature in use at the time the description was written.
BALANOSPHYRA FORMICIVORA BAIRDI (Ridgway)
The above common name is well chosen, as this is one of the commonest and most conspicuous birds throughout its range in California. Anyone who spends much time afield in the valleys, foothills, and canyons of southern and western California is sure to see this strikingly colored and active woodpecker making itself conspicuous among the oaks and pines; and, where one is seen, there are almost sure to be others, for it is a sociable species.
Referring to the Lassen Peak region, Grinnell, Dixon, and Linsdale (1930) say:
Two environmental factors of seeming importance for the presence of this bird were an available supply of acorns and wood or bark of sorts into which the birds could bore storage holes. As to species of oak, out of the six or more present, our impression remains that no outstanding choice by the woodpeckers was shown. About as many of the birds were seen among the black oaks in the vicinity of Payne Creek P. 0., as among the valley oaks around Cone's. However, tracks of black oaks recurred east of the main mountain mass in the section, as along the upper Susan River and near Eagle Lake, where no California woodpeckers were ever seen by us. To repeat, none of this species of woodpecker was seen by us east of about the western edge of the yellow pine belt (Transition life-zone). * * *
Situations where individuals of this woodpecker were observed are as follows: top of sycamore; dead sycamore stub; in cottonwood; about clumps of fruiting mistletoe; at tips of twigs of large valley oak; in black oak; in blue oak; on dead upper limb of living blue oak; in orchard tree; on isolated digger pine; in large yellow pine; at top of dead incense cedar; on ground at roadside; on fence post; on barn end; on telephone pole.
Courtship: I first became acquainted with this handsome woodpecker in the Arroyo Seco, 011 tile outskirts of Pasadena, during the winter and spring of 1929, where I often saw these birds busy with their courtship activities in the tops of the tall sycamores. They were flying about among the treetops, making a lot of noise, two males sometimes chasing a female and showing off their brilliant colors, the white spaces in their wings and the white rumps being especially conspicuous; doubtless the red crown and yellow throat, set off by black and white, played an important part in the display. They reminded me of flickers, as they danced on, or dodged around, the branches in playful, showy antics.
Nesting: Bendire (1895) writes:
In the more southern portions of its range nidification commences sometimes as early as April, and somewhat later farther north. The nesting sites are mostly excavated in white-oak trees, both living and dead, but preferably one of the former is selected in which the core of the tree is decayed. It also nests occasionally in sycamores, cottonwoods and large willow trees, and more rarely in telegraph poles. Both sexes assist in the excavation of the nesting site, as well as in incubation. The entrance hole is about 1% inches in diameter, perfectly circular, and is sometimes chiseled through 2 or 3 inches of solid wood before the softer and decayed core is reached. The inner cavity is gradually enlarged as it descends, and varies from 8 to 24 inches in depth, usually being from 4 to 5 inches in diameter at the bottom, where a quantity of fine chips are allowed to remain, on which the eggs are deposited.
Milton P. Skinner writes to me: "On May 12, 1933, I found a nest in the main trunk of an almost dead black oak. The opening, 25 feet above the ground, seemed very small and was placed on the southeast side of the tree.
"In tile Yosemite Valley, these birds nest in the trunks and large limbs of the Kellogg oaks, and their abandoned holes may be used by pygmy owls another year. As a rule, the California woodpeckers and the pygmy owls show little antagonism toward each other. In spite of this usual custom of nesting in the oaks, most of the birds I saw in the Yosemite were actually in the cottonwoods along the river. After some searching, I found at least one nest there in a short, dead stub of a cottonwood, on July 24, 1933. I saw one bird fly down and feed another that was inside, and then fly away. The hole was about 12 feet above the ground and on the north side of the stub, facing the river and away from the meadow behind it. All the trees in the vicinity were cottonwoods, but there was one oak 150 feet east of the nesting site. There were six other holes in the stub, all on the north side and from C to 18 feet above the ground."
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 whicb 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 beea prospected for nesting sites by woodpeckers: tbe 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 he the disappearance of woodpeckers. The question arises here as to the justification of the administrutiton 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 m