McAtee (1911) states that “about four-fifths of the insect food of the three species of sapsuckers consists of ants, the eating of which may be reckoned slightly in the birds’ favor. The remainder of the food is made up of beetles, wasps, and a great variety of other insects, including, however, practically no wood-boring larvae or other special enemies of trees. The birds’ vegetable food can not be cited in their behalf, as it consists almost entirely of wild fruits, which are of no importance, and of cambium, the securing of which results in serious damage.”
F. E. L. Beal (1895) mentions, as articles in the sapsucker’s diet, the berries of dogwood, black alder, Virginia creeper, and wild black cherries. Winfrid A. Stearns (1883) says: “Nuts, berries, and other fruits vary its fare; and to procure these it may often be seen creeping and hanging in the strangest attitudes among the terminal twigs of trees, so slender that they bend with the weight of the bird.” Audubon (1842), in his plate of the sapsucker, gives an animated picture of the bird thus engaged.
Brewster (1876a) shows the bird as an expert flycatcher. “From an humble delver after worms and larvae, it rises to the proud independence of a Flycatcher, taking its prey on wing as unerringly as the best marksman of them all. From its perch on the spire of some tall stub it makes a succession of rapid sorties after its abundant victims and then flies off to its nest with bill and mouth crammed full of insects, principally large Diptera.”
Behavior.—The sapsucker, a bird of wide distribution and in some parts of its range the commonest woodpecker, has come to be regarded with disfavor by man, who accuses it of harming the trees it drills to obtain its food. Man accuses the bird of weakening trees by drawing away their life-blood and of killing many by girdling them with multiple punctures, and he blames the bird for marring the beauty of trunk and limb by pitting and scarring them.
A study of the habits of the sapsucker shows that its work on the trees varies with the season and, on the Atlantic coast, is spread over a territory 3,000 miles long or more. During the migrations, northward and southward, when the birds are scattered and on the move, comparatively little harm is done. Here and there a limb may be killed—either girdled or opened so that infection enters—and rarely a tree may die, but the chief effect is an esthetic one, the scarring of the bark with pits, notably in orchards where it is a matter of common observation that most of the pitted trees are in perfect health. On their breeding ground and in their winter quarters, however, where the birds are concentrated and remain in one locality for a considerable time, the effect is more serious. In the Southern States especially, the lumber industry suffers material financial loss due to the fact that deep in the wood cut from trees on which sapsuckers have worked extensively, when the trees were small, the grain is distorted and made unsightly by the scars of the wounds inflicted by the birds years before.
From an exhaustive study of the economic status of the woodpeckers by W. L. McAtee (1911), the salient points in reference to the yellow-bellied sapsucker are quoted below:
The results of sapsucker attacks on trees are so uniform and characteristic as to be distinguished easily from the work of other woodpeckers. Sapsucker holes are drilled clear through the bark and cambium and often into the wood. They vary in outline from circular to squarish elliptical, in the latter case usually having the longer diameter across the limb or trunk. Generally they are arranged in rings or partial rings around the trunk, but they often fall into vertical series. Deeply-cut holes arranged with such regularity are made only by sapsuckers.
After the original pattern of holes is completed, the sapsuckers often continue their work, taking out the bark between holes until sometimes large areas are cleanly removed. This often occurs on small limbs or trunks, where long strips of bark up and down the tree are removed, leaving narrow strings between. This effect is also produced by continually enlarging single punctures by excavating at the upper end, * * * which is done to secure fresh inner bark and a constant supply of sap. Occasionally, after a tree has been checkered or grooved after the above-described systematic methods, it may be barked indiscriminately, leaving only ragged patches of bark. * * * Even in such cases, however, traces of the regularly arranged punctures are likely to remain, and there is no difficulty in recognizing the work as that of sapsuckers, for no other woodpecker makes anything like it on sound, living trees.
All holes, grooves, or irregular openings made by sapsuckers penetrate at least to the outermost layer of sapwood or nongrowing part of the tree. This results in the removal of the exterior rough bark, the delicate inner bark or bast, and the cambium. Since the elaborated sap (upon which the growth of trees depends) is conveyed and stored in these layers, it is evident that sapsuckers attack the trees in a vital part. Each ring of punctures severs at its particular level part of the sap-carrying vessels, another ring made above destroys others, and so the process continues until in extreme cases circulation of elaborated sap stops and the tree dies. When the injury to the vital tissues is not carried so far, only a limb here and there may die, or the tree may only have its vitality lowered for a few years. If the attacks cease, it may completely recover. * * *
Recovery, however, does not mean that the tree has escaped permanent injury. Patches of cambium of varying size may be killed. Growth ceases at these points and the dead and discolored areas are finally covered by wood and bark. Until this process is completed, the tree is disfigured by pits with dead bark and wood at the bottom, and even when completely healed, the spot remains a source of weakness. In fact, all sapsucker pecking is followed by more or less rotting and consequent weakening of the wood, and renders trees more liable to be broken by the wind or other causes.