70 Department of Conservation of Louisiana 



sponsible for 14,804 mice. If, however, predatory mam- 

 mals, or anything else, should destroy at the beginning, half 

 these eight mice, involving two females, the number at the 

 end of two years would be only half of 14,804, or 7,402. It 

 therefore is readily seen that the absence at the present 

 time of natural checks is not the important factor but that 

 their absence when the increase in population began was 

 the important factor that might have prevented or at least 

 greatly decreased the eventual outbreak. 



' 'Although suitable shelter was abundant for the mice, 

 it was not of the kind that would have been impregnable 

 to the enemies of the mice. Although food was abundant, 

 no evidence is forthcoming that it was more abundant than 

 in similar fields elsewhere at times when the weather condi- 

 tions were essentially as they were in the past two years 

 at Buena Vista Lake. As Hinton has said, The weather 

 may be lenient to rodents, the carnivora never.' At Buena 

 Vista Lake the carnivores had been eliminated. 



"The causes of this over-abundance of population of 

 house mice may therefore be stated as : favorable meteoro- 

 logical conditions, abundant food and shelter, and removal 

 of the principal natural enemies of small rodents that nor- 

 mally hold their numbers in check. The factor determining 

 the time of the spectacular emigration of the mice was, 

 probably, the destruction of their food and shelter. 



"Unfavorable meteorological conditions alone, a lesser 

 amount of food and shelter alone, would have, and the pres- 

 ence of the normal number of carnivorous mammals alone 

 might have, prevented the excessive increase in numbers." 



The foregoing comments on periodic fluctuation among 

 mammals, especially applying to the rodent family, to which 

 division our muskrat belongs, have been included for the 

 sole purpose of attracting the attention of readers of this 

 bulletin to this phase of our wild animal life to act as an 

 incentive to those with an investigative turn of mind to 

 make first-hand studies of the phenomenon. 



Field studies of the muskrat in Louisiana appear to bear 

 out the fact that our principal fur animal has five-year 

 cycles of abundance. This observation, however, it must be 



