ECOLOGY OF ISLE ROYALE. 397 



suggestive for its bearing on the question of the origin of the Caribou 

 upon the Isle. John Erickson was fishing through the ice, about 5 

 miles out from Pigeon Point, Minn., and at one time saw 11 Caribou 

 on the ice in the direction of Isle Royale. This clearly suggests a satis- 

 factory method by means of which these animals could easily reach the 

 island. 



Ecological Notes. — According to Canton, Caribou frequent marsh and 

 swamp grounds, a characteristic which is in decided harmony with the 

 physical conditions of the area it inhabits. It is adapted to these con- 

 ditions in several ways, as is shown not only in its feeding upon plant 

 life and frequenting damp and wet places, but also in the character of 

 its feet. Caton ('77, p. 90) says: "In traveling through the snows, or 

 soft marshy ground, the Caribou throws his hind feet forward, so as to 

 bring the leg into something of a horizontal position, spreads wide his 

 claws, and broad accessory hoofs, and thus presents an extraordinary 

 bearing surface to sustain him on the yielding ground, and so he is 

 enabled to shufBte along with great rapidity, where any other large quad- 

 ruped would mire in a bog, or become absolutely snowbound. The Rein- 

 deer [Caribou] alone leaves in his track the marks of all four of his 

 hoofs belonging to each hind foot, and specimens show the effects of 

 attrition on these secondary hoofs, and prove that they serve a useful 

 purpose in the economy of the animal." Still another adaptation is of 

 interest. During winter, the frog of the Caribou's hoof is entirely re- 

 sorbed (Elliot, '02, p. 268), thus producing a sharp rimmed concave sur- 

 face well adapted for walking upon the ice. 



In addition to the swamp plants used for food, the branches and 

 leaves of trees are frequently eaten, but the characteristic food is the 

 "reindeer lichen or moss" {Cladonia). This lichen is very abundant on 

 Isle Eoyale where the soil is too shallow and physical forces too severe 

 for most other plants to grow, as on the south shore of the island ( V, 2) 

 and upon the ridges. These lichen growths are very character- 

 istic of the area over which the Caribou ranges in Northeastern North 

 America. The region has been so recently glaciated and the soil removed 

 so that extensive patches of these lichens occur scattered through the for- 

 ests and are as characteristic of the region as are its swamps and conifer- 

 ous forests. This kind of food is therefore of general occurrence through- 

 out its geographic range. 



The female Caribou is remarkable in the possession of antlers, a char- 

 acteristic in the deer family, as a rule, of males only ; they are, however, 

 much smaller in size than those of the male. Caribou antlers are 

 further remarkable for their variety of form, the antlers from the same 

 individual, according to Caton ('77, p. 89), having as little in common 

 as those from different individuals. The old males, as a rule, shed their 

 antlers annually before the last of December, but the young males retain 

 them longer, the yearlings till spring and the females still later, until 

 after the young are born. 



The breeding season, according to MacFarlane ('05, pp. 679, 678) 

 occurs in September and October, and the young, one or two, are born 

 the following spring. 



The migration habits of Caribou are of considerable interest and may 

 have an important bearing upon the differentiation of the Woodland and 

 52 



