232 CONSERVATION OF CANADIAN WILD LIFE 



Muskrat. — The muskrat appears to be subject to peri- 

 odic fluctuations, but the conditions which affect the abun- 

 dance of this animal would tend to affect the regularity of 

 such fluctuations. Excessively wet seasons would cause un- 

 usual flooding of the marshes; or an extremely dry season, 

 especially if severe frost followed, would cause wide-spread 

 mortality among the muskrats, thus affecting their subse- 

 quent abundance. 



When we examine the fluctuations of such animals as 

 the wolverene, the black bear, the raccoon, the otter, and 

 the beaver, we find that there are no distinct fluctuations 

 shown by these animals. There are fluctuations, it is true, 

 but they are irregular in character and not sufficiently pre- 

 cise to warrant our regarding them as being of a periodic 

 nature. 



Conclusions. — From the foregoing discussion it will be 

 seen that we may divide the animals considered into three 

 main groups. First, the herbivorous rodents such as mice 

 and rabbits, which are very prolific and increase in numbers 

 until they reach an abundance which causes overcrowding, 

 when an epidemic of disease almost wipes them out and 

 their numbers rapidly decrease to a minimum. Second, 

 we have the numerous predatory animals which depend for 

 their subsistence either directly or indirectly upon the mice 

 and rabbits. These animals exhibit fairly regular periodic 

 fluctuations in numbers, their abundance being correlated 

 with the abundance of the animals upon which they feed, 

 although, as we pointed out in the case of the fisher, there 

 may be a distinct periodic fluctuation which does not appear 

 to be directly related to the fluctuation in the numbers of 

 any particular food animal. Finally, we have the animals 

 that feed on a mixed or exclusive diet of insects, vegetable 

 products, fish, or miscellaneous diet, that do not show any 

 marked periodic fluctuations. 



The economic value of this study in enabling us to pre- 



