ECOLOGY OP ISLE ROYALE. 405 



conditions brought about by baseleveling and glaciation — the poor 

 drainage, as shown by the innumerable swamps, ponds and lakes and 

 their small and sluggish streams. 



In addition to the great abundance of the food plants there is the 

 further favorable physical condition of deep snows, which fall before the- 

 soil or ponds freeze to a great depth, and thus make conditions favorable 

 for beavers on account of the protection afforded from deep frost, which 

 may close up the entrances to their burrows, houses, etc. 



4. PeromysGus canadensis uml)rintis? Miller. Isle Eoyale White- 

 footed Mouse. This mouse was perhaps the most abundant mammal 

 upon the island. It occurred in a great variety of situations as is indi- 

 cated by specimens taken at the following stations ; I, 3, 4, 7 ; III, 4, near 

 6 ; V, 1, 3, 4 ; I, '04 ; and II, '04. These stations include a variety of condi- 

 tions, balsam-spruce forests, tamarack and arbor vitae swamps; second 

 growth of birch following a burn, and specimens were even taken in the 

 Light-house. As thei*e was some doubt as to the identity of ' certain 

 specimens secured in 1904, the entire series of 55 specimens, including 

 46 taken in 1905, were sent to the Biological Survey and have been ex- 

 amined by Mr. W. H. Osgood who pronounced them unibrinus? [=-f- 

 man/iculatus Wag. ef. N. A. Fauna, No. 28, p. 41, 1909.] 



Ecological 'Note>s. — Almost nothing is known of the life history of the 

 variety utnhrinns ; it is only known from the vicinity of the northern 

 shore of Lake Superior and KecAvatin and the typical form P. canadensis 

 fares but little better because the accounts of P. leiicopns are confused 

 with it. It seems safe to conclude, however, that it is a forest inhabit- 

 ing species feeding upon seeds and nuts, but Preble ('02, p. 50) reports 

 it as invading houses in Keewatin and as rare in swamps. It is also 

 probable that they are active during the winter, at least on Isle Eoyale. 

 The Beaked Hazel (Corylus rostrata) perhaps furnishes them part of 

 their winter food. 



Geographic Range. — Known elsewhere only from Peninsular Harbor 

 (types), and Nipigon, Ontario. Compared with the typical form this is 

 a dwarf and melanic variety. A similar dwarfing and darkening of this 

 species occurs upon Eoan Mt., N. C, and upon the mountains of south- 

 western Penn. (var. nuMtetrae) . A third variety, abietonmi, occurs in 

 Nova Scotia. The typical form of the species ranges from New Bruns- 

 wick, western Massachusetts and central New York to northern Michi- 

 gan and the north shore of Lake Superior, in Ontario. 



5. Evotomys gapperi (Vigors). Eed-backed Mouse. Although our 

 parties trapped extensively in the vicinitj' of our camps, during 1904 and 

 1905, yet no specimens of this mouse were secured. The authority for 

 its occurrence upon the island is the 10 recorded specimens (Nos. 7725, 

 9966 to 9974) given by Coues ('77, p. 145) and collected by B. A. Hoopes. 

 These mice were "excessively abundant and universally distributed" on 

 the shore of Lake Superior according to Miller ('97, p. 15). It is therefore 

 surprising that is was not secured in abundance on Isle Eoyale. 

 Michael Hollinger described to Max M. Peet a mouse which the house 

 cat had caught during the winter and brought to the Club House. 

 There were two of these specimens, which were described as reddish 

 brown, short tailed mice, and which Hollinger said were quite dififer- 



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