DOWN UNDER 
     
    
   
   
    
     In these times of chilly days and chil- 
     
     lier nights, it is perhaps appropriate 
     
     to remind ourselves that many Island 
     
     residents have no home or shelter to 
     
     protect them from the wintery blasts. 
     
     But, due to down and underfur, these 
     
     residents are doing quite nicely, 
     
     thank—you. 
     
    
   
   
    
     Our own species, being one of the few 
     
     unfurred mammals of the world, has been 
     
     able to inhabit northern areas only be- 
     
     cause we have diligently copied the in- 
     
     sulative techniques used by other mam- 
     
     mals and birds. Indeed, the way we 
     
     construct our winter clothing can be 
     
     used to illustrate how the birds and 
     
     mammals, the originators of effective 
     
     body insulation, dress themselves for 
     
     cold weather. 
     
    
   
   
    
     There are three basic layers to any in— 
     
     sulating system, whether it is designed 
     
     to retain warmth in a house, in a fox, 
     
     in a duck, or in you. The outermost 
     
     layer must be tough and able to resist 
     
     the abrasive effect of the elements, and 
     
     depending upon specific requirements, it 
     
     must be water resistant or waterproof. 
     
     In a house, this role is fulfilled by 
     
     the shingles and wall boards; in a mam- 
     
     mal, by a layer of long, stiff hairs 
     
     called guard hairs; in a bird by the 
     
     contour feathers which are firmly rooted 
     
     in specific parts of the body called 
     
     feather tracts; and in a person's coat, 
     
     -by the layer of cotton or nylon that 
     
     forms the outer covering. 
     
    
   
   
    
     The next layer is the one that actually 
     
     keeps the heat in. Houses have fiber- 
     
     glass insulation, mammals have fine 
     
     soft fur called underfur, birds have 
     
     down feathers, and our own coats may 
     
     have any insulation the manufacturer 
     
     cares to stuff them with. 
     
    
   
   
    
     The third layer is of course the inside 
     
     layer, which prevents the insulation 
     
     from falling inwards. Plaster walls 
     
     play this role in houses, as do the 
     
    
   
   
    
     inner lining of coats, but in the case of . 
     
     birds and mammals, the inner lining is the 
     
     skin itself, which is the living tissue 
     
    

    
     that gives rise to both the middle layer 
     
    

    
     (down or underfur) and the outer layer 
     
     (contour feathers or guard hairs). 
     
    
   
   
    
     It is worthy of note that even those parts 
     
     of our bodies that are furred are not very 
     
     effectively insulated, because all human 
     
     hair is guard hair of poor insulative qual- 
     
     ity. On the other hand, the natural insul— 
     
     ative system of other warm-blooded animals 
     
     is highly efficient; indeed, waterfowl down, 
     
     on a per weight basis, is the most effective 
     
     barrier to heat transfer known to man. 
     
    
   
   
    
     Birds and mammals that spend a large part of 
     
     their time in the water have a critical re— 
     
     quirement for effective covering, since 
     
    

    
     it is essential that the water be kept away 
     
     from both the insulative layer and the skin 
     
     below. This is done by the secretion of 
     
     oils, either from tiny glands associated 
     
     with hair roots, or from the "preen gland" ‘ 
     
     on a bird's rump. It is not for vanity that 
     
     aquatic birds and mammals spend a great deal 
     
     of time greening and grooming, but rather 
     
    

    
     to ensure that the oils are spread uniformly 
     
     and the coat is completely waterproofed. 
     
    
   
   
    
     In recent years both down jackets and fur 
     
     coats have enjoyed exceptional consumer 
     
     popularity. But even those who are clad in 
     
     coats of other materials can take comfort in 
     
     the fact that the principles of coat con- 
     
     struction have stood the test of millions of 
     
     years of evolution on the part of the birds 
     
     and mammals that originated them. 
     
    
   
   
    
     David Cairns