410 MICHIGAN SURVEY, 1908. 



but find relatively few small bodies of water, which are so abundant 

 farther north. Except along the coast, these habitats are generally 

 or relatively isolated, in striking contrast with their relative proximity 

 in the north. These southern muskrats as a rule especially those in- 

 habiting streams do not construct houses, but live in burrows. 



Turning now to the northern part of the muskrat's range, from Lab- 

 rador to the Mackenzie basin and southward into the glacial lake belt — . 

 the most extensive lake and swamp area on earth, — muskrats are found 

 in the greatest abundance and development. Here instead of the rela- 

 tive isolation, as in the more southern part of its range, it finds an 

 almost continuous habitat, of considerable geographic extent, and it 

 is in this area that they are lodge builders, in addition to being bur- 

 rowers, especially those that live about the swampy margins of ponds 

 and lakes. This general change of habits between northern (Minnesota) 

 and southern (Ohio) muskrats was pointed out by the Herrick (cf. 

 '91, pp. 15-18; or Herrick '92, p. 212). 



It is thus seen that a close relation exists between the habits and 

 the habitats of this animal; tbus, whether or not they live in burrows 

 or lodges, is determined, in part, by the local topography and geological 

 history. Such observations show the need of detailed locality studies 

 of animals, in which the interrelations of the habits and the environ- 

 ment will be given primary attention. Prom such investigations, it 

 will in the future be possible to prepare maps showing the topographic 

 and geographic distribution of habits, just as other characteristics of 

 the North American mammals, such as color, dimensions, etc. have 

 been carefully investigated and mapped. But so far as known to the 

 writer, no particular attention has been given to this phase of geo- 

 graphic problems. The muskrat would furnish an excellent subject 

 for such an investigation on account of its extensive range, abundance 

 and evident response to its environment. 



But before leaving this subject, attention should be directed to the 

 fact that while the above remarks apply primarily to the Muskrat, yet 

 they have a much more general bearing, and apply equally well not 

 only to many animals, but also, it is probable, to the habitat relations 

 of many plants. 



7. Lepus americamis Erx. Hudson Bay Varying Hare. With the 

 possible exception of the White-footed Mouse, the Hare is the most 

 abundant mammal upon Isle Royale. In all 27 specimens were taken 

 rrom the following localities: I, 2, 3, 6; II, 2; III, 4, 5; V, 3, 4; I. 

 '04, VIII, '04 and V, '04. Evidence for their presence occurred at the 

 following additional stations : I, 5 ; II, 3 ; IV, 5, 9 ; and VII, '04. It is 

 thus seen that their distribution was quite general and their abund- 

 ance was equally characteristic. Although frequently found in the for- 

 est there was an apparent preference for open areas. This was sug- 

 gested by the well defined paths or runways seen in sphagnum 

 swamps, in Cladonia openings and on the jack pine ridges. 

 The shallow soil with its attendant rock openings combined to produce 

 an extensive area of favorable habitats for them; supplementing this 

 is an abundance of vegetable food and a relatively small number of 

 carnivora. 



Ecological Notes. — The food habits seem to be quite varied as shown 



