368 FRANCIS H. HERRICK 



of excavation in detail, but ^Yish to point out the following 

 facts : The gourd-shaped chamber which results is as typical 

 in form and measurements as the clay cup of a robin or the 

 elastic pouch of an oriole. The diameter of the entrance is 

 highly uniform for the species, and often as truly circular as 

 if cut with an auger. Both sexes work, and the time of building 

 which may extend over a week, depends in a measure only upon 

 the hardness of the wood. According to Audubon the ivory 

 bill regularly chooses a living tree, and I have seen a spruce 

 telephone pole successfully worked by the red -head. Like so 

 many other species, the flicker will occasionally adapt natural 

 cavities, and has been known to nest in the sawdust of an ice 

 house or even to burrow in a haystack. The same flicker's 

 hole may be used for a second brood, or by the same or other 

 birds for a series of years. That holes are used as winter quarters 

 is not to be doubted, but if such are dug out for this purpose 

 the fact is interesting, though not without analogies in other 

 species. Moreover, if a breeding pair be disturbed they will 

 sometimes abandon their hole and excavate another, but this 

 does not always follow; the same hole may be taken and deep- 

 ened " Compare such conduct with that of a vireo (see p. 258. 

 Part ii), which abandons a new nest \\'ith or without egg.i through 

 fear, but uses it as the site for building a new one, the result 

 giving us a compound or superimposed nest, in the lower sec- 

 tion of which a cowbird 's egg may be concealed. 



The chickadee which not only adapts a natural hole but digs 

 with great labor an artificial one, flies away with every chip 

 removed and drops it at a distance, male and female working 

 in alternation. The red-bellied nuthatch like the chickadee will 

 use a natural cavity or dig one in wood, in which case it is care- 

 ful to collect drops of freshly exuded pitch and smear them 

 about the entrance. The efi:ect of this is supposed to discourage 

 intruders, but this appears doubtful; it may represent the echo 

 of an instinct to narrow the opening as seen in the European 

 nuthatch already noticed, and suggests the behavior of the 

 tropical hornbills (see p. 170, Part ii). 



The building habits of the belted kingfisher {Ceryle alcyon) and 

 the bank swallow {Clivicola riparia) are similar to this extent 



*^ See Audubon; Op. cit. vol. ii, p. 75. Edinburgh, 1S34. 



