As to the height from the ground, P. B. Philipp writes to me that of 26 nesting holes examined by him in New Brunswick two were 15 feet, two 12 feet, three 10 feet, one 8 feet, two 6 feet, two 5 feet, four 4 feet, six 3 feet, and four only 2 feet above ground.
Although the Arctic three-toed woodpecker usually nests at no great height above ground, there are a few exceptions to this rule, mainly in the western portion of its range. Grinnell and Storer (1924) record a nest seen in the Yosemite region that was 50 feet above ground in a dead lodgepole pine. Harry S. Swarth (1924) found, in the Skeena River region, the highest nest of which I can find any record; he says: “A nest of the Arctic three-toed woodpecker was found in Kispiox Valley. It was placed in a dead and charred Engelmann spruce, in a strip of spruce woods bordering a muskeg otherwise surrounded by poplar forest. The nest hole was eighty feet from the ground. It was two and one-half inches in diameter and one foot deep, drilled through an outer sheath of sound, hard wood, and downward through soft, rotten ‘punk.’”
Eggs.—The number of eggs laid by the Arctic three-toed woodpecker varies from two to six, four being the commonest number. These vary from ovate to elliptical-ovate, the former shape prevailing. The shell is dull or only slightly glossy and is pure white. The measurements of 39 eggs average 21.32 by 18.94 millimeters; the eggs showing the four extremes measure 25.9 by 18.7, 25.1 by 20.2, and 22.35 by 17.53 millimeters.
Young.—The period of incubation is about 14 days; both sexes assist in this and in the care of the young. Only one brood is raised in a season, but if the eggs are taken, a second set will be laid, often in the same nest.
Mr. Achilles (1906) watched a nest containing young for 24 consecutive hours, he and a companion taking turns at the vigil and sleeping alternately within ten yards of the tree; he writes:
The parents, when feeding their young, usually alighted within a space of three feet below the hole, and never directly at its entrance. They would pause here for a moment as though fearing they were observed by someone. Then they would hop up to the hole and look in, anywhere from two up to six times, as if accustoming their eyes to the darkness. Once in a while grubs could be seen in their bills, but, from the actions of the birds when feeding their young, they appeared to be regurgitating. During twenty-four hours the female fed the young thirty times, and the male twenty-nine times.
As it grew dusk, the young gradually grew quieter, and their little “peep-peep-peep” greatly resembled those of chicks when crawling beneath their mother’s wings. From two o’clock in the afternoon till seven o’clock that evening, two minutes was the longest period during which the young did not utter a single “peep.” From seven P. M. until two minutes after four the next morning, the young birds ceased this continuous chattering. The mother was the last to feed them at night, the time being seventeen minutes after seven; but the male was up first in the morning. At four-fifteen in the morning, the young uttered a few sleepy “peeps,” and the male alighted three feet below the hole at four-sixteen. The young birds heard him alight and immediately commenced to chatter. The male hopped up to the hole, looked in twice, and then fed them. The young birds’ bills were seen, indicating that they were very hungry, and were hanging on to the inner wall of the nest near the entrance. Soon after this their hunger was appeased, their bills were seen no more, and the parents had to go almost into the hole to feed them.
Plumages.—The nestlings are naked and blind at first, but the juvenal plumage is acquired before the young leave the nest. In the juvenal plumage, the young male is similar to the adult male, but the yellow crown patch is smaller and not so sharply defined; the upper parts are duller, browner black, lacking the glossy, bluish edgings; the breast is tinged with dull buffy white; and the flanks are more heavily and less distinctly barred or spotted with dull black. The young female is similar to the young male, but there is no distinct yellow patch on the crown, only scattering yellow feathers in varying amounts, often few or none at all. This plumage is worn through the summer and early fall; the first winter plumage, which is practically indistinguishable from that of the adult, is apparently not fully acquired until November or December. Adults have one complete annual molt, beginning in August.
Food.—More than three-quarters of the food of both species of three-toed woodpeckers consists of the larvae of wood-boring beetles, mainly Cerambycidae and Buprestidae. Referring to the former, Prof. F. E. L. Beal (1911) says:
Stomachs containing 15 to 20 of these grubs are very common, and one held 34. Probably the stomach is filled several times each day, and it does not seem unreasonable to assume that a bird will eat 50 of these insects every 24 hours for 6 months and at least 25 daily for the other half of the year. At this rate one bird will annually destroy 13,675 of these destructive grubs. * * *