WOODPECKERS 329 



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, extend- 

 ing 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 numer- 

 ous 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 



