;28 



ANIMAL LIFE IN THE YO SEMITE 



from that of most other woodpeckers, which forag'e extensively on dead 

 timber and drill live wood only when in search of boring insects. 



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 splin- 

 ters 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 result- 

 ing 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. 



Diagram of workings of Sierra 

 Eed-breasted Sapsucker, showing how the bird 

 drills through the bark to reach (b) the soft 

 growing tissue (cambium) where sap is mov- 

 ing rapidly. Inset figure (a) shows general 

 arrangement of workings on trunk of tree. 



