COMMON ROCK WREN 287 



learn, these small stones are used as a foundation for the nest, or are 

 mixed with the material of the nest. In some cases the stone walk 

 extends 8 or 10 inches out from the nest. The stones vary in length 

 from half an inch to 2 inches or a little more, and it seems remarkable 

 that the slender bills of the birds are strong enough to carry them, 

 often for a considerable distance. The reasons for this curious 

 habit, which seems to be so universal, are not well understood. In 

 some cases the stones are piled up so high at the entrance that only the 

 flattened body of the wren can enter, thus possibly forming a barrier 

 to entering enemies. Or, they may serve as direction marks to help 

 the owners to find the home crevice. But neither of these theories 

 seems wholly satisfactory ; perhaps some day we may know the answer. 

 The rock wren is, I believe, the only permanently resident land bird 

 on the Farallone Islands, where it seems to breed abundantly among 

 the rocks. Milton S. Ray (1904) found about 20 nests there, including 

 old and new. He says : 



Whether the nest was in a niche in the cliffs, beneath a rock fence, or under 

 a gi'anite ledge cropping out above the surface, it was always placed among 

 rocks firmly embedded and never amid the loose rocks that lay scattered about 

 on the top of the ground. * * * By far the most elaborate nest I found was 

 in the rear of the Stone House ; it ran in the earth among the rocks of a rock 

 fence. A shelf-like stone at the entrance formed a sort of veranda, and this the 

 birds had literally covered, as well as the main corridor leading to the nest. I 

 noticed the pavement was equally deep under the nest, and that all the tiny 

 nooks and crevices on the way were filled. I carefully counted all the stones and 

 other material in this earthen burrow between the bare granite boulders, and 

 as it was situated 2 feet up in the wall the birds had undoubtedly brought all 

 of them. 



His list of materials follows: One safetypin, 2 pieces of wire, 2 

 pieces of a pair of scissors, 10 pieces of zinc from old batteries, 2 fish 

 hooks, 2 pieces of glass, 1 piece of leather, 4 copper tacks, 2 pieces of 

 limestone, 4 pieces of plaster from the walls of the house, 12 pieces of 

 shingles (some as large as 2 by 3 inches), 9 bits of abalone shells, 20 

 bits of mussel shells, 106 rusty nails, 227 bits of flat rusty iron, 492 

 small granite stones (very regular in size), and 769 bones of rabbits, 

 fish, and birds, as well as the usual nesting material. 



He continues : "The birds in this case had easy access to all the little 

 bits of material that accumulate around dwellings; but even then, 

 what a vast amount of patience and labor, as well as perception, it 

 required to find and transport the 1,665 listed objects, to say nothing 

 of building the nest itself ! This was composed of the bird's favorite 

 substance, excelsior packing, together with a few weeds and grasses 

 and bits of cotton and rabbit fur tucked in decoratively here and there, 

 and measured 5i/4 inches over all, while the cavity was 3 inches across 

 by iy2 inches deep." He suggests that lining the passageway and 

 placing stones under the nest may serve to keep them free from damp- 



