Preface xiii 



the innate urge that forces a grouse to expose itself in order to 

 perform for the benefit of other grouse— these and many other 

 conditions predispose the predation which actually disposes of tlie 

 grouse. The lack of adequate shelter in the cover, an inconvenient 

 distribution of staple food supplies, man's sudden changes in the 

 habitat, are examples of environmental deficiencies that may induce 

 grouse mortality from predator attack. The density of the grouse 

 population itself affects the degree of predation. 



Even under the best of physical circumstances, predators will 

 affect grouse population to some degree, and over most of the north- 

 eastern range they constitute one of the major factors. Many other 

 mammals and birds that are associated with grouse habitat tend to 

 serve as buffers for grouse by furnishing the predators with the bulk 

 of their food. 



DISEASES AND PARASITES 



Organisms that derive both food and shelter from the grouse are 

 parasitic upon it. Those that live upon its skin are ectoparasites and 

 belong to the insects and other arthropoda. Endoparasites, those that 

 live inside the body, are generally roundworms, flatworms, or free- 

 floating protozoa or bacteria. Some of the disease-causing organisms 

 are classed as viruses, while one is a fungus. Many are capable of 

 causing death, either alone or in combinations. 



Most animals have a rather large population of parasitic organisms, 

 even when in excellent health. This is true of grouse. Most specimens 

 of grouse when thoroughly examined will be found to have parasites 

 of various types. Ordinarily they do the bird no harm. When certain 

 destructive kinds gain access, the bird may be seriously affected. 

 Other kinds of parasites, when present in large numbers, may have 

 serious effects. 



Generally a grouse, so ill from the effects of parasitic organisms 

 that its functions are impaired, is picked off by some enemy before it 

 can die from its affliction. Some do actually die without violence, 

 at times in such numbers that the presence of an epidemic is in- 

 dicated. 



When disease is rampant it is a grave matter. Fortunately this is 

 not commonly the case, and the direct losses from this source are 

 generally occasional and scattered 



