FLUCTUATIONS OF FUR-BEARING ANIMALS 219 



region of northern Alberta, in 1915, signs of the recent 

 abundance of rabbits were everywhere. For miles along the 

 trails the young growth of poplar had been barked and 

 girdled by the hordes of rabbits during the previous winter. 

 But hardly a rabbit was to be seen; they had almost com- 

 pletely disappeared. 



The cause of the sudden plague which kills off the rab- 

 bits when they reach their greatest abundance so that the 

 whole countryside is overrun with them is probably of a 

 multiple nature. The chief factor is undoubtedly over- 

 crowding. This results in an epidemic of various parasitic 

 diseases to which rabbits are susceptible, particularly one 

 of bacterial origin, which speedily spread throughout the 

 rabbit population of the affected territory. 



Constituting as it does the chief food of many of the 

 larger fur-bearing animals, such as lynx, fox, and wolf, the 

 rabbit is one of the most important factors in determining 

 the abundance of these animals. 



Lynx. — The lynx is primarily dependent upon the rabbit 

 as a source of food, although it also devours mice, grouse, 

 ducks, stranded fish, young deer, or sheep. Its periods of 

 abundance, therefore, correspond with those of the rabbit. 

 Preble states that the winter of 1903-04 was remarkable 

 for the abundance of lynxes throughout the upper Mackenzie 

 region, this abundance of lynxes being accounted for by the 

 enormous numbers of rabbits in the same region at that 

 time. Following the last outbreak of rabbits to which I 

 have referred, lynxes were very abundant, according to the 

 reports that I have received, during the winters of 1914 and 

 1915. When the rabbits had disappeared there was a re- 

 markable southern migration of lynxes throughout the 

 northwest, and, during the winters of 1916 and 1917, they 

 were taken in districts in the Prairie Provinces, whither 

 they had migrated in search of food in more southerly locali- 

 ties than they have been recorded as visiting for many 



