160 THE STORY OF THE BIRDS. 
Besides the placing of the head under the wing 
practiced by many birds, many small sleepers make 
special dispositions of their plumage as a sort of night 
robe. They usually fluff it up till their shape is much 
changed. It has been asserted that this is done to pre- 
vent their heat’s radiation, but it is more likely a simple 
protective measure whereby the appearance of the 
body is made quite unbirdlike at least, and often very 
like a knot on the limb. A few birds feel safer on a 
bare perch where they can see around well, as turkey 
vultures and others. 
