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- 
