346 APPENDIX F 



Slave River. Here we saw one or two during the evening of 

 July 17, and again noted several on our return trip on September 

 25. (See Chapter XV.) 



The species multiplies in cycles as does the rabbit, reaching 

 great numbers, and then dying, some think of a disease; but 

 others say the mortality is due chiefly to weather conditions. 

 Thus wet weather after the ice comes causes high water over 

 the ice. The rats are forced out on the ice to wander in search 

 of a new pond with available food and are exposed to countless 

 dangers. T. Anderson has known 8 killed in one day as they 

 were running on the ice; this was in February. Low water is 

 equally dangerous, for the ponds then freeze to the bottom and 

 the rats starve in their lodges, or, as before, are forced out to 

 travel in search of water. G. Daniels found as many as 10 or 

 15 dead in the lodges in one colony during 1905. If overtaken 

 when crossing the open country, the muskrat usually turns and 

 fights desperately. 



They are much preyed on by mink, but commonly escape by 

 diving. A rat can swim 100 yards under water, a mink not 

 more than a third as far. 



Castor canadensis Kuhl. Canadian Beaver. 



The beaver is generally distributed throughout the region 

 covered on our trip north to near the tree limit, but has been 

 nearly exterminated from most of the region by persistent trap- 

 ping. The only point where we found it at all common was the 

 Nyarling, where we saw many burrows and houses and a num- 

 ber of the animals. We were told that the species is now in- 

 creasing on the lower Athabaska. 



Erethizon dorsatum (Linn.). Canada Porcupine. 



The porcupine, originally rather common throughout the 

 region, has lately become rarer in most places. We saw none, 

 but obtained a number of notes from Indians and others regard- 

 ing its recent occurrence. Robillard told us that he had killed 

 a porcupine at a point about twenty miles east of Fort McKay, 



