n6 MOUNTAIN AND MOORLAND 



find that they are moulted late in autumn, the worn 

 sheath slipping off and disclosing a fresh growth 

 well suited for all the scratching for food that is 

 required in winter. Just as the Puffin moults annually 

 the outer covering of its quaint bill, so the Grouse 

 moults its claws, and in so doing both birds are, so to 

 speak, declaring their distant relationship to reptiles, 

 which periodically cast off the outer layer of the skin 

 which covers the scales. 



In his enquiry into grouse disease (1911) Sir Arthur 

 Shipley found that there were eight different kinds of 

 insects and mites living on the outside of the Red 

 Grouse and no fewer than fifteen different kinds of 

 parasites living in the interior unpaying boarders. 

 Two of these are especially important : a transparent 

 Threadworm that frequents part of the food-canal 

 (there may be 10,000 in one bird), and a microscopic 

 single-celled animal, called Coccidium, which lives in 

 countless numbers in the wall of the food canal in 

 young Grouse. Now the young stages of the minute 

 Threadworm are found squirming among the leaves 

 of the Heather, and it is by eating the heather that 

 the Grouse is infected. The other side of it, however, 

 is that the Heather is externally infected with the 

 Threadworms by droppings from the Grouse. These 

 contain eggs which hatch in a couple of days into 

 microscopic worms, which after resting for a while 

 become active wanderers, ascending the Heather and 

 other plants, especially after rain. When Grouse are 

 in vigorous health it seems that they can tolerate, as 

 many other living creatures can, a considerable con- 

 tingent of parasites. A sort of " live-and-let-live " 

 partnership is established. But the Grouse may get 



