92 WATERPROOF FEATHERS. 



but stands every way ; and thus is very elastic as 

 well as warm and light. 



The different apportionment of this downy part of 

 their clothing to the several climates and elements in 

 which birds move, as well as to their habits, is very 

 remarkable ; and many of the swimming birds can 

 remain for days in water very little above freezing, 

 and yet sustain no inconvenience from the action 

 either of the cold or of the water. 



The feathers of birds are in themselves, to a con- 

 siderable extent, water-proof, and all birds are more 

 or less furnished with glands near the base of the tail 

 which secrete an oily liquid. This liquid the birds can 

 reach and extract \vith their bill and apply it to the 

 feathers, by drawing these between the mandibles. 

 This operation forms part of the process of preening 

 or trimming the feathers, in which birds occupy a 

 portion of their time. They do this for three pur- 

 poses to strain the water from such feathers as get 

 wet, to smooth the webs of such as get ruffled, 

 and to apply the oily secretion as occasion mav 

 require; and they also make use of the bill in 

 removing those decayed feathers which become 

 incumbrances instead of being useful to the birds in 

 their motions. 



FEATHERS OF FLIGHT. 



As introductory to the notice of these, it may 

 not be improper to remark that, generally speaking, 

 the nearer that the clothing feathers of birds approxi- 

 mate to the form of flying feathers, they are always 

 the more firm and perfect in their structure ; and 

 that this holds not only in different species of birds, 

 but in the plumage of the same species during it> 

 progress to maturity. There is even a gradation 



