NESTS AND NEST-BUILDING IN BIRDS 273 



in this case stand out boldly from a black background. These 

 nests, though dissimilar in outward appearance, agree in all 

 essential respects, in the treatment of the outer and inner wall, 

 and in the dimensions of the cup. The differences are unim- 

 portant, because plainly due to different environments. 



Variations in Hummingbirds' nests. The hummingbirds' nests 

 examined pertain to the ruby throat {Trochilus colitbris), from 

 the eastern states, the Anna (Calypte anna), the black-chinned 

 (T. alexandri) and Allen's hummiingbirds {Selasphorus alleni) 

 from California, and the broad tailed hummer (5. platycercus) 

 from the Santa Rita Mountains, Arizona. ^^ 



Hummingbirds build the smallest and most delicate nests 

 known, ^* but the examination of their work brings out the same 

 kind of facts which we have seen in dealing with other and larger 

 species. There seems to be not only a general agreement in the 

 nests of different species and genera, but a striking uniformity 

 in essential characters, and this is the more pronounced when 

 different specimens of the same species are examined. 



Hummingbirds exhibit the tendency to saddle their nests on 

 small twigs and at a point where they fork (fig. 17); at times 

 the base of their nest is continued around the main support, 

 thus affording greater security. The ruby throat and Allen's 

 hummingbird first spread an adhesive plaster of saliva on the 

 chosen twig, and building upon the wafer thus formed literally 

 glue their nest to its support like the swift. Whether this is 

 an invariable practise or not could not be decided from the 

 material at my command. All build of the finest and softest 

 vegetable substances, in which the microscope reveals plant 

 down and pappus of various kinds, the hairy coats of seeds, bud 

 scales and the petals of flowers. In the nests examined animal 

 products were limited to the nestling and small contour feathers 

 of birds, a few horse hairs, and in one instance, peculiar short 

 quills suggesting those of a hedgehog, but probably coming 

 from a bird. (See fig. 17.) 



The materials of the nests examined, whatever their appear- 

 ance or quality, are treated in a similar way, being felted and 

 molded more or less compactly, and bound with spiders' silk. 



^^ For the privilege of examining these nests I am indebted to Dr. W. H. Valway, 

 and Professor Hugh D. Pallister. 



3'' With the possible exception of the tree swifts: see p. 171, of part 1. 



