WILLIAMSON SAPSUCKER. Sphyrapicus thyroideus thyroideus (Cassin)

Field characters.—A woodpecker, in size slightly smaller than robin. Male: Black, with rump and large patch on fore part of wing white. (See pl. 6). Female: General color tone pale; head light brown, rump white; plumage elsewhere narrowly barred with black and light brown. A bird of notably quiet demeanor. Voice (not often heard): A weak wheezy whang or whether.

Occurrence.—Common resident of Hudsonian and upper Canadian zones on both slopes of Sierra Nevada. Observed from near Chinquapin eastward to Walker Lake. One record for floor of Yosemite Valley: December 29, 1914. Restricted closely to lodgepole pine belt.

The distribution of the Williamson Sapsucker in the Yosemite region is complementary to that of the Sierra Red-breasted Sapsucker; in other words the two birds do not overlap in range to any important extent. The present species is a high mountain bird, being found only in the upper Canadian and the Hudsonian life zones. It is non-migratory; only rarely is an individual detected in lower zones and then only during the midwinter months. The Williamson Sapsucker is, like its relative of lower altitudes, a quiet bird, rarely uttering its weak note, and never, so far as known to us, drumming in the noisy manner so characteristic of certain other woodpeckers.

Of all species of North American woodpeckers, the Williamson Sapsucker is the most remarkable because of the striking differences in plumage between males and females, and between adults and young. (See pl. 6). The only color mark of the species common to both sexes, at all ages, is the white rump. Otherwise, males are chiefly black, with a large white patch on the fore part of the wing (and not across the flight feathers as in the California and White-headed woodpeckers). There is also a white stripe backward from the bill across the cheek, and another behind the eye. The black of the adult male plumage has a slight greenish iridescence, while that of the young male is more sooty and of a softer texture. The young have the chin white, this white being replaced by red in the adult plumage.

Females are entirely different. They are narrowly barred with black and light brown or white on the back, wings, sides of body and tail, and the head is uniformly light brown. Old adult females have a spot of solid black on the breast, which the younger birds lack. Adults of both sexes have the middle of the belly bright yellow, whereas in the young of either sex this area is chiefly white. Thus, in each sex, the young is most nearly like the adult of that sex: the young male does not at all resemble the adult female, a condition contrary to rule among other birds the adults of which are of different coloration. Young males acquire the adult plumage, even to the red chin spot, at the first fall molt, and by mid-September are in fine feather. Young females acquire most of the adult characters at this same molt save perhaps the black breast spot. The marked differences in plumage between the two sexes in this sapsucker led the early naturalists, in the fifties, to designate the male and female as separate species, and they were so considered until 1874; one author, at least, went so far as to place them in separate genera!

In the Yosemite region the Williamson Sapsucker is closely associated with the lodgepole pine. While this tree seems to furnish the bird's preferred source of forage, practically all other species of trees within its local range are also utilized. We saw workings attributable to this sapsucker on the alpine hemlock, red and white firs, Jeffrey pine, and quaking aspen.

Fig. 44. Close view of fresh work of Williamson Sapsucker on lodgepole pine. Photographed at Porcupine Flat, July 1, 1915; about 1/8 natural size.

The amount of work which this sapsucker will do upon a single tree was impressed upon us while we were at Porcupine Flat in early July, 1915. In that locality there was a lodgepole pine (Pinus murrayana) about 60 feet high, which showed no marks of sapsucker work previous to the current year. The tree was in full leafy vigor and measured 8 feet 3-1/4 inches in girth at 3 feet above the ground. There were numerous live branches down to within 6 feet of the ground. Twenty-six irregularly horizontal rows of fresh punctures were counted on one side of the trunk, the lowest being only 18-1/2 inches above the ground, and the highest about 40 feet. (Part of one series is shown in fig. 44). No one row of pits completely encircled the tree; a branch had in every instance interfered with the bird's completing the row at that level. But opposite the end of any row, from 1 to 4 inches up or down the trunk, there was the beginning of a complementary row, showing where the sapsucker after ascending to clear its tail or descending to clear its head of the obstructing branch, had continued puncturing in the sidewise direction. Up and down the tree the rows of punctures were from 3 to 24 inches apart. The horizontal length of one series of pits 6 feet above the ground was 35 inches; of another close by, 44 inches. Individual punctures in a row were 0.4 to 0.6 inches (10 to 15 mm.) apart. Three typical fresh punctures all measured 0.16 inches (4 mm.) high, with respective widths of 0.2, 0.37, and 0.4 inches (5, 9, and 10 mm.). The nearly constant vertical dimension, just as in the case of the drillings of the Red-breasted Sapsucker, was probably due to the size of the bird's bill, while the varying horizontal dimension resulted from varying amounts of work done in the individual pits. Many of the holes were bleeding and probably would have been visited again and again by the sapsucker. Earlier drillings of the current season had stalactite-like streamers of hardened pitch below them, some being 2 feet in length.

Fig. 45. Result of work of Williamson Sapsucker on bark and trunk of old lodgepole pine. Photographed at Porcupine Flat, July 1, 1915. See discussion in text.

In addition to the exudation of sap, these series of puncturings cause responsive growth action on the part of the tree. Rings or swellings in the wood and bark develop at the sites of the punctures. A tree drilled to the extent of the one described above would in a few years show a series of swollen rings, one at each line of punctures (fig. 45). And the site of each individual puncture develops into a small knot-like growth. A dead lodgepole pine at Aspen Valley showed clearly that it had been drilled extensively in earlier years; for the dead and partly barkless bole was little more than a succession of swollen rings. Many trees exhibiting intermediate stages in this scar-like affliction were observed.

During the winter months when sap is practically at a standstill in the coniferous trees at high altitudes, the Williamson Sapsucker must needs seek other fare. A few of our own observations added to those of other naturalists suggest that during the winter season the birds may forage in large part on dormant insects or on insect larvae hidden in crevices in the bark. If such is the case, whatever the damage done by these birds to the forest as a whole during the summer months, it is partially offset by their winter-time activity. In any event, the attacks of the Williamson Sapsucker on the lodgepole pines of the central Sierra Nevada cannot be considered as of great economic importance, for these trees are there used little if at all for lumber or for any other commercial purpose.

Several points of importance in regard to the economic bearing of sapsuckers in California remain to be worked out satisfactorily. A prime need is definite knowledge as to the real nature of their food—whether sap, inner bark, growing wood, or insects; and if all of these, the proportion of each in the diet for the entire year.

Several instances of the nesting of Williamson Sapsuckers came to our attention. At Mono Meadow on June 20, 1915, a nest was located 16 feet up in a partly dead lodgepole pine. The tapping of the bole of the tree brought forth a chorus of cries from the young birds within. Two days later, at Peregoy Meadow, an adult was seen carrying ants in its bill, probably on the way to feed its brood. At Tuolumne Meadows on July 13, 1915, another nest was discovered about 20 feet above the ground in a dead lodgepole pine. As the observer stood watching the site the female sapsucker swooped past him and alighted on the trunk of the tree above the nest hole. Then she backed down and clung in front of the hole. The notes of the young increased in volume as the mother bird put her bill, laden with ants, through the entrance. It would seem that wood ants are important as an article of diet for the young, at least while they are in the nest. The marked trait of adults of this species, to go directly to the nest hole when feeding the young and not to approach indirectly, as do so many birds, makes the discovery of nests relatively easy.