The Relations of Breeding Yellow-Bellied Sapsuckers to Wounded Birches and Other Trees

Abstract

Wm.E I was studying Yellow-bellied Sapsuckers (Sphyrapicus varius) on their breeding grounds in central New Hampshire (Kilham, 1953(Kilham, , 1956(Kilham, , 1962)), it became apparent to me that birch trees (Betula) were often used as sources of sap when young were in the nest or had emerged to become part of a family group.The species involved were the white (B.papyriJera), yellow (B.lutea, var.alleghaniensis), and gray (B.populiJolia) birches.Sapsuckers also feed on a variety of other trees (McAtee, 1911).Regardless of the trees utilized, however, it is not always obvious why they concentrate on a single tree here and there, leaving many others untouched.In the summers of 1962 and 1963, I found three areas well suited to study of this problem.One, Area A, centered on groups of white birches growing along a dirt road (Figure 1), where snow plows and undercutting of banks had produced both injuries and weakening.This area was the territory of Pair A. Areas B and C were occupied by seven other pairs of sapsuckers and consisted of woodlands where hundreds of unwanted or weed trees had been girdled as part of a forestry management program. AREA AConditions in 1962.--Practicallyall of the birches used to any extent by the pair in Area A, in the initial year of its territory (1962), had old scars below the feeding areas.While 10 birches with snow plow injuries all had drill holes (Figure 2), 50 others of similar size and adjacent to them, but unwounded, had no holes.The main feeding places of 1962, however, were on white birches which stood back from the roadway, beyond reach of the snow plow.Two of these trees were located in the midst of 80 healthy birches in a patch of woodland between two fields (Figure 1).Both had extensive scars of unknown origin below the drill holes.Two additional birches, the largest of those used by Pair A, had black, fungating infections of Poria obliqua below the bands of holes.Each of these latter trees appeared to be weakened, one by having its roots exposed in the undercutting of a roadside bank and the other from exposure following lumbering operations.The second had over 900 drill holes.Drilling o] "satellite" trees.--&varius frequently makes small bands of drill holes, some of which may be expanded into main feeding bands in a succeeding year.These initial holes were always on birches within 1 to about 15 feet of a main feeding tree, at the same height (Figure 3), and were usually facing it.There was no obvious sap flow from such bands, which 520