450 THE AGE OF MAMMALS 



{Cervus canadensis) is recorded (F. W. Putnam) as far south as Florida. 

 According to Thompson-Seton ^ the range of the wapiti in prehistoric times 

 did not extend south of the thirty-tliird parallel (i.e. to northern Georgia, 

 Alabama, and Texas). 



Migrations of birds in Pleistocene times. — Allen-' believes that "the 

 Glacial Period left its impress upon the majority of northern birds, through 

 the development in them of the habit of migration, for it is now generally 

 conceded that this habit must have originated in consequence of a great 

 reduction of temperature at the close of the Tertiary. Prior to this period, 

 owing to the comparatively uniform climatic conditions then obtaining 

 almost everywhere, there could have been no necessity for extended pe- 

 riodic movements. During the waning of the ice period the areas offering 

 a congenial summer home to a great multitude of birds became greatly 

 extended, from which, however, they were driven by semi-arctic winters to 

 seek favorable winter haunts farther southward. In this way it is believed 

 the habit of migration has become established as an irresistible hereditary 

 impulse as mandatory as the 'instinct' of reproduction.'* 



The same author speaks elsewhere {op. cit., p. 101) of the "over-crowded 

 tropics." "On account of the flight of all animal life before the successive 

 advances of the great ice sheet there was a crowding together of exiles 

 from the north into the more favored regions to the southward, leading to 

 an intense struggle for existence and a weeding out on a grand scale of forms 

 least fitted for the contest. This period must have been one of great 

 activity in the evolution of new types. Opportunity was given for the 

 gradual adaptation of many forms to lower temperatures than those to 

 which they had been accustomed, and to an enforced change of food. The 

 recession of the ice field at the close of the Glacial Epoch was accompanied 

 by the gradual extension northward of habitable land. A broader area 

 became available in summer than in winter, and an annual migration for a 

 great or less distance on the part of pioneer life became a necessity." 



Insect life. — To throw some light on the effect of the Glacial Period 

 on the insect life of North America, Scudder ^ instituted a careful comparison 

 of the number of endemic species in the northern part of the eastern states 

 {i.e. the area once covered by the ice sheet) and of the Pacific coast (where 

 it is claimed no ice sheet covered the face of the country), and also to deter- 

 mine how many species were common to north and south, in the East and 

 in the West. If there were found no signs of poverty in the fauna of the 

 regions of former glaciation, we may say that the East has fully recovered 

 from the shock of the Glacial Period. The beetles {Coleoptera) were chosen 



1 Thompson-Seton, E., The Wapiti and his Antlers. Scribner's Magazine, Vol. XXXIX, 

 no. 1, Jan., 1906. 



- Allen, .J. A., The Geographical Origin and Distribution of North American Birds, 

 Considered in Relation to Faunal Areas of North America. The Aiik, Vol. X, no. 2, April, 189.3. 



3 Scudder, S. H., The Effect of Glaciation and of the Glacial Period on the Present Fauna 

 of North America. Amer. Jour. Sci., Vol. XLVIII, Sept., 1894, pp. 179-187. 



