MORTALITY AMONG BIRDS. 113 



not aware of it. But then he adds, " the case is 

 just the same with blackbirds," &c. * Here I should 

 be disposed to doubt the fact altogether of these 

 birds being fatter in frosts than at other times. They 

 may appear to be so ; but it is appearance only, and, 

 as I imagine, simply an expedient to which they re- 

 sort in order to keep up better the temperature of 

 their bodies in cold weather. By ruffling up their 

 feathers, they admit the air between them, which is 

 a worse conductor of heat than the feathers them- 

 selves, at the same time that it removes further from 

 their bodies the conducting surface by which their 

 natural heat would be carried off; just as a loose 

 cloak about the person is warmer than one which fits 

 closely to it. The conducting surface itself also is 

 less effective when the feathers partially stand up 

 than when they are smoothed down; though the 

 feathers radiate more freely under the former condi- 

 tion than under the latter. This is according to the 

 known laws, by which, caeteris paribus, bodies radiate 

 and conduct heat according to the nature of their 

 surfaces. 



MORTALITY AMONG BIRDS. 



IT has been thought by some a matter of surprise, 

 that we so seldom meet with dead birds,-)- notwith- 

 standing the immense multitudes that must die every 

 year. It is said that man destroys few, comparatively 

 speaking ; and it is asked what becomes of the re- 



* Letter V. to Daines Barrington. 



t Jesse's Gleanings, Second Series, p. 296. 



