ECOLOGY OP ISLE ROYALE. 407 



The geographic and topographic isolation of these varieties is worthy 

 of special notice. The occurrence of a local firm (loringi) of a forest 

 inhabiting speciee, in the forested valleys upon the plains is of special 

 interest in showing how topographic and geographic influences may 

 fayor isolation. 



6. 'Fiber sibetliicus (Linn.). Eastern Muskrat. No specimens 

 were taken by our party in 1905, but two specimens were found in 1904, 

 at Washington Harbor by Max M. Peet (I, '04) ; and early in the spring 

 of 1905 Charles Preulx secured one specimen from the same place — the 

 small island near the mouth of Washington Creek. A few additional 

 locality records were secured this season. Victor Anderson, the trap- 

 per, reported muskrats abundant at Sumner Lake (III, 5), and numer- 

 ous broken Anodonta grandis footiana Lea shells were found there by 

 N. A. Wood. Similar broken shells of the same form — were also found by 

 Wood at Sargent's Lake^ while I found such shells abundant at the end 

 of the McCargoe Cove trail (II, 4). John Anderson reported muskrat 

 houses at Fish Island Bay and at Tobin Harbor during the fall of 

 1904. There is an abundance of Anodonta and Lampsilis upon the i.s- 

 land, especially of the former, which occur upon sandy shores, such as 

 are found near the head of Eock Harbor. It may be a question as to 

 how much broken shells should be taken as evidence of the presence 

 of Muskrats, but the trapper's statements of occurrence are in harmony 

 with the evidence from the shells. Perhaps part of the damage to 

 these should be credited to the Mink. 



Mike Johnson, fisherman, reports that he has seen the Muskrat at 

 Chippewa Harbor. Mr. J. N. Malone, Keeper of Menagerie Island 

 Light, several years ago found a, Muskrat in the cellar of the Light- 

 house (X, 10), and caught two near the camp in Siskowit Bay (V, 3). 



Ecological Notes. — The Muskrat is one of the most generally known 

 of our native mammals but although much has been written of its 

 habits, much more is yet to be learned. In several respects its habits 

 are similar to those of the Beaver, although they are not at all closely 

 related. Thus both are aquatic, burrowing, house-constructing animals 

 \\dth submerged entrances to their houses. Both have been reported 

 (Morgan, '68, p. 138) to exhale under the ice, and after allowing the 

 bubbles a moment's exposure, to reinhale them, and continue their 

 journey under the ice. Such similiarities, if true, are very interesting 

 because they illustrate the independent acquirement of similar traits 

 along distant lines of descent; due apparently to the influence of sim- 

 ilar environments. 



The life history is about as follows, but apparently varies in differ- 

 ent localities. Thus in Pennsylvania, the young, according to Rhoads, 

 ('03, p. 105) are born "at all seasons." This statement seems remark- 

 able as Kennicott ('57, p. 107) states that "from five to seven young — 

 more or less — are produced in April or May," and Merriam ('86, p. 

 283) states that in the Adirondacks of New York "It brings forth from 

 five to nine young at a birth, and is said to raise three litters in a sea- 

 son." Farther north in Saskatchewan (MacFarlane, '05, p. 738) re- 

 ports that the females are said to begin breeding when about a year old 

 and give birth to "but two litters the first, and three each succeeding 

 season for a time." The number of young in each litter varies from S 

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