DAMAGE TO POLES. 11 



now changing some 300 poles on this account," he writes. The poles 

 injured ' ' are round cedar, square redwood, and also round creosoted 

 poles; the latter were only placed within the line within the last 

 two or three years. The square poles seem to suffer the most; in 

 many cases we find five or six holes of 3 or 4 inches in diameter in 

 one pole. It seems to be the object of the woodpeckers to dig into 

 the pole for insect life, which the pole may contain, although we 

 find places where they have made nests. The hum of the wires, I 

 think, has something to do with attracting the birds to the poles, 

 which sound they take to be insect life in the pole." (Aug. 17, 1910.) 

 Besides the species already mentioned, the following are known 

 to injure telephone poles to a greater or less degree: Texan wood- 

 pecker (Dryobates s. bairdi), St. Lucas woodpecker" (Dryobates s. 

 lucasanus), California woodpecker (Melanerpes f. bairdi), red-bellied 

 woodpecker (Centurus carolinus), yellow-shafted flicker (Colaptes 

 auratus), and red-shafted nicker (Colaptes c. collaris). The California 

 woodpecker, besides making nest cavities, perforates the entire sur- 

 face of poles with small holes in which to store nuts. (See PI. IV, fig. 

 1.) However, "decay is the great cause of destruction of poles. It 

 is estimated that approximately 95 per cent are destroyed by this 

 cause and only 5 per cent by breakage or mechanical abrasion." 1 

 How much of the breakage is due to the weakening of posts by wood- 

 peckers is unknown, but the damage is nowhere near as great as com- 

 monly supposed. Mr. Howard F. Weiss, of the Forest Service, dis- 

 cusses the effects of woodpecker attack on poles, in the Engineering 

 News of February 23, 1911 (vol. 65, No. 8, p. 220), from which we 

 quote at length : 



The number of holes in each pole may vary from one to a dozen or more, although 

 these larger numbers are not common. The size of the hole varies from about J to 3 

 inches diameter. When used for nesting sites the birds may hollow out a pocket 6 to 

 10 inches in diameter and a foot or more in depth. 



The question of interest to telephone engineers is to just what extent such poles are 

 weakened. The following example may be of interest. It has been found from 

 measurements on two hundred and fifty 30-foot northern white-cedar poles that their 

 average taper is approximately as follows: 



Circumference Distance from butt 



(inches). (feet). 



43 



37 5 



36 6 



34 10 



32 15 



29 20 



27 25 



24 30 



1 Bureau of Census, Forest Products, No. 10, p. 106, 1909. 



