ECOLOGY OF ISLE ROYALE. 415 



and another on the ridge north of Beaver Island. Fish were used as 

 bait. 



Ecological Notes. — The breeding season occurs but once a year, dur- 

 ing February and March, and the young, 6 to 8 in a litter, are born 

 blind. Their nests are made preferably in hollow trees, under logs, 

 and in holes in the ground (MacFarlane, '05, p. 711), or by robbing a 

 squix'rel of its nest (Coues, '77, p. 95). Its food consists of mice, 

 squirrels and rabbits, supplemented by other small animals such as 

 birds and their eggs, frogs, toads, fish, etc. 



This animal, as well as the Hare and Lynx, shows the same kind of 

 periodical variation in abundance, and MacFarlane ('05, p. 710) brings 

 forward the following interesting observations bearing on this subject: 

 "In years of plenty the marten is very numerous throughout the entire 

 northern forest region; but is not uniformly so at the same time in 

 every section of country all over the immense territories covered by 

 the Hudson's Bay Company's trading operations. When it is abundant 

 or scarce, say in the northern and western departments, it will generally 

 be found that there is an important and corresponding increase or 

 decrease in the southern and Montreal departments. The natives main- 

 tain that lynxes and martens migrate from the north and west to the 

 east and south, and that when they have attained their height in num- 

 bers for several reasons, the great bulk (no section is ever totally 

 devoid of martens) of those who escape capture resume the return 

 march until the next period of protracted migration. It must be ad- 

 mitted that many old fur traders have come to entertain similar views 

 from their own personal experience and observation. I think the 

 aforesaid twerity-flve years' London sales statement adds strength to 

 the migration theory, and is otherwise of some interest." The natives 

 also maintain that there is a fluctuation in the birth rate correspond- 

 ing to this periodical abundance. Such migratory tendencies as above 

 mentioned could not help but have an important bearing upon the 

 geographic range and the interbreeding opportunities of these animals. 

 Oeograpliic Range. — The typical form of this species has a range 

 from Labrador; Nova Scotia; Massachusetts; Northern Pennsylvania; 

 Quebec; Ontario; Michigan, southern Keewatin; Saskatchewan; Al- 

 berta; south on the mountains into Colorado; Utah; northwestward 

 into eastern Oregon ; Washington and British Columbia ; and eastward 

 to Hudson Bay on the north (Rhoads, '02, p. 445). A second form, 

 of this species hrumalis, is restricted to the coast of Labrador; a 

 third, actuosa, ranges north of latitude 55° to the tree limit, from west- 

 ern Labrador westward to the Rocky Mountains nearly to the U. S. 

 boundary and westward to the Coast Ranges of British Columbia into 

 Alaska; a fourth form abieUnoides, is restricted to the interior of 

 British Columbia, the Selkirk and Gold ranges; and a fifth ahieticola, 

 is only known from Saskatchewan. So much differentiation of the 

 type seems rather remarkable when combined with the marked migra- 

 tory tendencies of the species and suggests that these wanderings may 

 not be as extensive as has been supposed or that these movements are 

 quite local in character. 



10. Putorius vison (Schreber). Northeastern Mink. Three speci- 

 mens of mink were secxired at Isle Royale. One was taken at camp 

 55 



