SIERRA RED-BREASTED SAPSUCKER. Sphyrapicus varius daggetti Grinnell

Field characters.—A woodpecker, in size decidedly smaller than robin. Whole head, throat, and breast, rose-red or crimson (pl. 5d); back and wings black, spotted with white, rump white; a stripe of white along wing when folded. Whole demeanor of bird very quiet. Voice (seldom heard): A single low note, churr, or cheer-r-r, burred at end.

Occurrence.—Common in summer in parts of Transition Zone and lower portion of Canadian Zone on west slope of Sierra Nevada; found also at Walker Lake, on the east slope, in same season. Winters in Upper and Lower Sonoran zones on the west side. Seen in Yosemite Valley during fall and early winter months; earliest record, September 16, 1920 (C. W. Michael, MS). Forages in both deciduous and evergreen trees.

Two woodpeckers of a particular type known as Sapsuckers are found in the Yosemite region throughout the year, and a third variety of the same category visits the region during the winter. The subject of the present account, the Sierra Red-breasted Sapsucker, is found in the main forest belt during the spring, summer, and fall, but regularly performs an altitudinal migration which carries it down into the tree growths of the western foothills and valleys for the winter months.

Sapsuckers, of whatever species, seek mainly the juices and to a less extent the softer wood (bast and cambium) of the trees. Hence they work only on living trees, and their relation to the forest is entirely different from that of most other woodpeckers, which forage extensively on dead timber and drill live wood only when in search of boring insects.

Fig. 43. Diagram of workings of Sierra Red-breasted Sapsucker, showing how the bird drills through the bark to reach (b) the soft growing tissue (cambium) where sap is moving rapidly. Inset figure (a) shows general arrangement of workings on trunk of tree.

The Sierra Red-breasted Sapsucker is in our experience well-nigh voiceless and its work is done in such a quiet manner that it does not ordinarily attract attention, as do the woodpeckers which are wont to pound noisily. The most vigorous drilling of the sapsucker will scarcely be heard more than a hundred feet away. The bird moves its head through a short arc, an inch or two at the most, giving but slight momentum to the blows. The chips cut away are correspondingly small, mere saw dust as compared with the splinters or slabs chiseled off by other woodpeckers. The strokes are delivered in intermittent series, four or five within a second, then a pause of equal duration, then another short series, and so on. From time to time a longer pause ensues, when the sapsucker withdraws its bill and gazes monocularly at the work. The cutting is done first on one side of the little pit and then on the other so that the resulting hole is wide, clear to the bottom, but usually only high enough to easily admit the bill. This shape of hole, exposing a greater breadth of the growing wood through which sap flows, brings the greatest amount of sap with the least expenditure of effort in cutting. The depth of the hole varies with the thickness of the bark, but it always reaches down into the soft growing layer of the wood (fig. 43).

Since the location of the drillings is not determined by the presence of any boring insect or larva within the tree, the pits are made in series, in rows transverse to the axis of the trunk or larger limbs; sometimes these series extend nearly around the bole, interrupted only where the bird has been halted by the presence of a branch. Were the holes made one above the other, only the bottom one (or top one, according to the season) would afford any considerable flow of sap; this premise is in part verified by the observation that when a certain tree was drilled repeatedly the newest holes were at the bottom of the series.

Soon after being drilled the holes made by the sapsuckers begin to bleed. The sap flows out and collects in the pits, or runs along in the crevices of the bark. The birds revisit the workings at short intervals, taking the exuded sap and any insects which have been attracted or caught by the sticky juice. Subsequently the drillings may be enlarged, until sometimes they become longitudinal series of flutings or grill work, extending up and down the tree for considerable distances.

The effect of these drillings upon the trees is obvious. Removal of the bark and growing layer of wood causes the trees to lose large quantities of the sap which is essential to growth, and exposes the adjacent parts to attack by fungi and insects. Occasionally the drilling is so continuous around the circumference of a tree as to completely girdle the bark, and thus eventually to cause the death of the tree. But the fact that it is a marked trait of this sapsucker to return again and again to the same tree, even year after year, rather than to seek new forage trees each season, means that only a relatively small number of trees are attacked. In all our field work in the Yosemite region we did not see over a score of trees which showed extensive work by this sapsucker.

The variety of trees worked upon and the seasonal differences in this bird's forage range can best be indicated by citing instances of the work of this species which came to our attention. At Snelling, where the bird is a winter visitant only, old pepper trees (Schinus molle) showed numerous drillings, and in the foothills near Pleasant Valley apple trees on the Campbell Ranch had been riddled with holes. At El Portal both digger pines and golden oaks had been drilled, one of the latter trees being heavily pitted on many of its upper branches. Near Sequoia a sugar pine five feet in diameter had an area approximately 3 by 40 feet in extent well grilled by Red-breasted Sapsuckers. Near Sweetwater Creek, a yellow pine had been pitted, and an oak tree showed vertical grillings where sapsuckers had evidently worked for a number of seasons. Several incense cedars were seen which showed abundant work by these sapsuckers. One of these trees at Hazel Green had large deep holes as big as the acorn caches of the California Woodpecker, the size being obviously dictated by the thickness of the cedar bark.

In the apple orchard in Yosemite Valley several trees showed extensive workings, both old and new, of this species, in addition to the less harmful borings by the Willow Woodpecker. Twice we saw 'blazed' scars on pine trees where red-breasted sapsuckers had taken advantage of the thinning of the bark to concentrate their drilling on the small area exposed.

The reason for the vertical migration of the red-breasted sapsucker to lower levels for the winter season is not readily apparent. It may be that the birds are ill adapted to seeking dormant insects during the winter months and so need to descend to lower altitudes where they may find in abundance soft-barked trees from which cambium may be easily obtained. Thus they may tide over the season when there is little or no flow of sap in the forest trees at higher levels.

At Tamarack Flat, on May 24, 1919, a Sierra Red-breasted Sapsucker called from high in a conifer and then flew down to an upstanding stub on a prostrate pine. The bird hopped about on this stub and on small fragments of limbs close to or even upon the ground. It would seem that just after the snow is gone bark foraging species (to which category the sapsucker belongs when not dependent upon sap), finding little forage on tree trunks, seek sustenance near the ground.

No nests of this sapsucker were located by us. A bird taken near Chinquapin on May 21, 1919, judging from the glandular condition of the skin on the abdomen, had already begun incubation; another individual collected near Tamarack Flat on May 25, 1919, was just ready to lay a set of 4 eggs.

Except for the occasional fruit trees attacked during the winter months, we do not believe that the role of the red-breasted sapsucker in the central Sierra Nevada is economically important. Its general predilection for deciduous trees and its habit of returning again and again to the same individual tree save the forest as a whole from any serious injury. Certainly the part of this bird in this respect amounts to very much less than the ravages resulting from parasitism by mistletoe, or from attack by insects or by fungous diseases of the bark, wood, or leaves.