NESTS AND NEST-BUILDING IN BIRDS 277 



These little pieces of lichen are glued together with the saliva 

 of the bird." 



It now seems that both sides to this controversy were partly 

 right and partly wrong. When we remove some of the incrusta- 

 tion from the outer wall of the ruby throat's nest and examine 

 it mounted in cold water under the microscope, the fibrous 

 matter is seen to consist of two kinds, namely vegetable fibers, 

 such as plant hairs, and strips of bast, and others of animal 

 origin; the latter, though extremely attenuated, prove to be 

 spiders' silk, for no change is produced by boiling the water; the 

 lichens, moreover, are lightly secured, and show no trace of 

 saliva before or after removal. We must therefore infer that the 

 only effective use which this hummingbird makes of its saliva 

 in such operations is in the wafer with which its nest is some- 

 times if not regularly glued to its twig support. What is true 

 of this t,pecies seems to hold for others, although the wafer was 

 found only in the anna and the ruby throat. The egg cocoon or 

 even the web of a spider is quite as serviceable to them as to a 

 wood pewee or a vireo. If it is true, as Audubon asserts, that 

 lichens are attached over the branch at some distance from the 

 nest, the fact is very interesting, but this did not occur in any 

 of the nests examined. 



That certain hummingbirds which build hanging and swaying 

 nests, sometimes compensate them by the addition of weights 

 in the form of stones or lumps of earth, has been more than 

 once reported, and a specimen of this kind may be seen in the 

 British Museum. We regard such singular acts as strictly anal- 

 ogous to building the base of a nest around its support, or in 

 favoring one side when the branch is inclined (see fig. i6), and 

 thus bringing the cup of the nest into an upright position what- 

 ever the angle, or indeed in sticking the nest to its twig by 

 means of an adhesive wafter. The structure and position of 

 these birds in relation to their general habits warn us of the 

 folly of reading a high degree of forethought and intelligence 

 into any such acts, however remarkable. 



