Bendire (1895) says:
The duties of incubation are divided between the sexes and last about two weeks. The young when first hatched are repulsive-looking creatures, blind and naked, with enormously large heads, and ugly protuberances at the base of the bill, resembling a reptile more than a bird. They are totally helpless for some days, and can not stand; but they soon learn to climb. They are fed by the parents by regurgitation of their food, which is the usual way in which the young of most Woodpeckers are fed when first hatched. * * * The young remain in the nest about three weeks. When disturbed they utter a low, purring noise, which reminds me somewhat of that made by bees when swarming, and when a little older they utter a soft “puirr, puirr.” Even after leaving the nest they are assiduously cared for by both parents for several weeks, until able to provide for themselves.
Plumages.—The young hairy, like all other young woodpeckers, is hatched naked, and the juvenal plumage is assumed while in the nest, so that when the young birds emerge they are fully fledged. In the juvenal plumage the sexes are sometimes much alike, though oftener there is a decided difference. In both sexes the bill is decidedly smaller, weaker, and more pointed than in the adult; the color pattern is almost exactly like that of the adult, but the plumage is softer and fluffier; the white markings are more or less tinged with yellowish, the two inner primaries are dwarfed, and the innermost white tail feather is usually tipped with black. The colored markings in the crowns of both sexes are very variable in color and in extent. L. L. Snyder (1923) has made a careful study of the crown markings of young hairy and downy woodpeckers of both sexes. He found that 90 percent of the young male hairies had more or less red, pinkish, or yellowish markings in the crowns, and only about 14 percent of the young females were so marked. But only 10 percent of the young males and about 43 percent of the young females had white markings only on a black crown; and about 43 percent of the young females had the entire crown black. There is great individual variation in the amount and in the distribution of these colors; the white spots are often mixed with the other colors; the reddish and yellowish colors may invade nearly the whole crown, exist in one or two large patches, or appear on only a few scattered feathers.
The juvenal plumage is worn but a short time; the molt into the first winter plumage is accomplished between July and October. This first winter plumage is much like that of the adult in both sexes, but the white spots are not quite so pure white, and the red nuchal patch of the male is duller and often interrupted. Adults have a complete postnuptial molt in August and September and perhaps a partial prenuptial molt in spring.
Food.—Various studies of the food habits of the hairy woodpeckers show that these birds are among our most useful birds and especially valuable as protectors of our forest and shade trees and orchards. More than 75 percent of their food consists of injurious insects, while the amount of useful insects and cultivated fruits that they destroy is insignificant. Prof. F. E. L. Beal (1911) has published the most exhaustive report on this subject, based on the study of 382 stomachs collected during every month in the year and from many parts of the range of the species, including practically all of the races. He says: “In the first analysis the food divides into 77.67 percent of animal matter and 22.33 of vegetable. The animal food consists of insects, with a few spiders and millepeds; the vegetable part is made up of fruit, seeds, and a number of miscellaneous substances.” Of the animal food, he says: “The largest item in the annual diet of the hairy woodpecker consists of the larvae of cerambycid and buprestid beetles, with a few lucanids and perhaps some other wood borers. These insects constitute over 31 percent of the food and are eaten in every month of the year. * * * One stomach contained 100 of these larvae and 83 and 50, respectively, were taken from two others. Of the 382 stomachs, 204, or 53 percent, contained these grubs, and 27 of them held no other food. Other beetles amount to a little more than 9 percent.”
Ants rank second in importance, amounting to a little more than 17 percent, and are taken every month in the year; other Hymenoptera are eaten in very small quantities and irregularly. Caterpillars are the next most important item, many of them wood-boring species, amounting to a little less than 10 percent. “Prof. F. M. Webster states that he has seen a hairy woodpecker successfully peck a hole through the parchment-like covering of the cocoon of a Cecropia moth and devour the contents. On examining more than 20 cocoons in a grove of box elders, he found only 2 uninjured,” according to Professor Beal (1911), who adds that bugs (Hemiptera) and plant lice (aphids) form only a small part of the food, and says: “Orthoptera, that is, grasshoppers, crickets, and cockroaches, are rarely eaten by the hairy. A few eggs, probably those of tree crickets, and the egg cases (oötheca) of cockroaches, constitute the bulk of this food. These with a few miscellaneous insects amount to a little more than 2 percent for the year. Spiders with their cocoons of eggs, including one jointed spider (Solpugidae), and a few millepeds, were eaten to the extent of about 3.5 percent, which completes the quota of animal food.”
He says further:
The vegetable food of the hairy woodpecker may be considered under four heads: Fruit, grain, seeds, and miscellaneous vegetable substances. Fruit amounts to 5.22 percent of the food, and was contained in 54 stomachs, of which 13 held what was diagnosed as domestic varieties, and 41 contained wild species. Rubus seeds (blackberries or raspberries) were identified in 4 stomachs, and were counted as domestic fruit, but it is perhaps more probable that they were wild. * * * Of wild fruit 18 species were identified. It constitutes the great bulk of the fruit eaten, and is nearly all of varieties not useful to man.
Corn was the only grain discovered in the food. It was found in 10 stomachs, and amounted to 1.37 percent. * * * The seed of poison ivy and poison sumac (Rhus radicans and R. vernix) were found in 17 stomachs, and as they usually pass through the alimentary canal uninjured, the birds do some harm by scattering the seeds of these noxious plants. * * * Cambium, or the inner bark of trees, was identified in 23 stomachs. Evidently the hairy does but little damage by denuding trees of their bark. Mast, made up of acorns, hazelnuts, and beechnuts, was found in 50 stomachs. It was mostly taken in the fall and winter months, and appears to be quite a favorite food during the cooler part of the year.
Illustrating the quantities of insects eaten by individual birds, F. H. King (1883), Wisconsin, writes: “Of twenty-one specimens examined, eleven had eaten fifty-two wood-boring larvae; five, thirteen geometrid caterpillars; ten, one hundred and five ants; six, ten beetles; two, two cockroaches; two, nine oötheca of cockroaches; two, two moths; one, a small snail; one, green corn; one, a wild cherry; and one, red elder berries. * * * One of the above birds had in its stomach eleven wood-boring larvae (Lamides?) and twelve geometers; another, thirteen larvae of long-horn beetles and four cockroach oötheca; another, nine wood-boring larvae; and two others together had three wood-boring larvae, and nine larvae not coleopterous.”