178 BULLETIN 17 4, UNITED STATES NATIONAL MUSEUM 



the floor of the passageway slopes downward, both inwardly and 

 outwardly, and this outward slope forms the bevel already mentioned. 

 The bowl at the bottom is 6 or 6V2 inches across. In a specimen before 

 me as I write, the wall of the chamber below the entrance hole is 4 

 inches thick. The ridge across the floor of the entrance passageway 

 is rounded. Its crest is 2i^ inches inward from the outer surface of 

 the tree trunk, and the vertical depth of the outward bevel is 2 inches. 

 All the surfaces of the cavity are neatly and uniformly chiseled. 

 Along the sides of the entrance passageway extend in parallel curves 

 the tool marks of the bird's beak. No nesting materials are brought 

 in. A feather or two will be the only trace of occupancy remaining 

 after the young are flown. In some though not in all cases it is pos- 

 sible for a man to thrust in his arm and reach the bottom of the 

 chamber. 



As a general rule, certainly, a new cavity is drilled for every brood. 

 Such exceptions as have been recorded have explanation in human 

 interference. Samuel Scoville, Jr. (1920), quotes Eichard C. Harlow 

 to the effect that but once in his experience had a second use of a nest- 

 ing cavity occurred. Afterward Mr. Harlow said to me in conversa- 

 tion that even in that instance the cavity had been deepened before it 

 was used for a second time. The only other instance that has come to 

 my attention is one recorded by Morrell (1901) in which a single cavity 

 was used three times — in 1895, in 1897, and in 1898. In preparation 

 for the third nesting the cavity had been deepened by three inches. 

 This nesting was in "a small patch of good sized trees * * * 

 separated [from] the main growth by cutting," and it may be sup- 

 posed that the woodpeckers had been unduly limited in the choice 

 of nesting sites. In both cases the birds were subject to the disturbance 

 of persistent egg-collecting. It stands to reason that, in avoidance 

 of parasites, the practice should have evolved of drilling a fresh cavity 

 for each brood. 



Mr. Harlow (1914) found that in one instance the drilling of the 

 nesting cavity was in progress in March and was continued "all dur- 

 ing March and April." The female worked alone, and the male con- 

 tinued near by. This nest, an unusually early one, contained, on 

 April 30, three eggs. In the Northern States the eggs commonly are 

 laid early in May. Incubation continues, according to Burns (1915), 

 for 18 days. The young leave the nest about the middle of June. 



The range of date in nesting is illustrated by two records that come 

 from Centre County, Pa. (Scoville, 1920; Burleigh, 1931). One is of 

 a set of eggs that hatched on May 11. These eggs must have been laid 

 before April 23. The other record is of a set collected May 11 and 

 found to be practically fresh. The interval at which these two cases 

 stand apart is about 25 days. Scoville (1920) quotes Harlow, a col- 



