Michigan Ornithological Club 19 



in Illinois, Indiana, Ohio and Michigan (*99, '02). In his reports Mr. 

 Lcverett gives maps showing the ancient glacial lakes and drainage lines, i 

 have adapted from his maps and from snggestions made by him the 

 following outline map. Fig. ::, which shows the most important lines of 

 glacial drainage, and such old shore lines as concern us at present. It is 

 not intended that these topographic features were of contemiioraneous age 

 as it is definitely known that such was not the case, but it is of significance 

 to know their origin and their infiuence upon bird life. To those who have 

 not seen these topographic features or given them any thought it may be 

 a surprise to learn that they form conspicuous features of the topography. 

 The beach ridges may in many cases be followed for many miles as a very 

 marked feature of the landscape. These drainage valleys have wide open 

 valleys or deep gorges so that they are very conspicuous. It should be 

 remembered that these are in a relatively level country, which tends to 

 exaggerate even slight topographic features. In this connection it is of 

 interest to note that two important highways of bird migration into the 

 lower peninsula of Michigan have been influenced to a large degree by glacial 

 drainage. In glacial times the St. Joseph river from South Bend, Ind.. 

 (Leverett. '97, p. 4:J8) flowed down the Kankakee river and emptied in turn 

 into the Illinois. This southwestern highway into Michigan has been sup- 

 plemented by contributions from the Wabash valley. The other highway 

 into southeastern Michigan has been by way of the Upper Wabash and 

 Maumee valleys. In glacial times the Wabash valley below Fort Wayne 

 formed the outlet of Lake Maumee (whose descendant in part, is Lake 

 Erie). Thus the forking of migration routes, at the western end of Lake 

 Erie, is apparently of ancient origin and in all probability began in early 

 post-glacial times. 



It is generally accepted that as the great continental ice sheet of the 

 Ice Age spread over northeastern North America, life was compelled to 

 extend its range to the south before it or become extermmated, and as the 

 ice melted away there began a return piovement. Such a statement has been 

 challenged, apparently on the basis that birds, as other organisms, do not 

 retreat from adverse conditions. This is the position maintained by Dixon 

 ('97, p. 20) in a very suggestive book on the bird migration. He further 

 maintains that the birds of the Northern Hemisphere never extend their 

 breedmg range soutliii'ard, and that southward extension of breeding range 

 during" the advance of the ice sheet is a myth. Even if it were granted that 

 organisms do not retreat from adverse conditions, it docs not necessarily 

 follow that there was no southward extension of the breeding range with 

 the southward advance of the ice. There can be but little doubt that there 

 were definite zones of conditions, similar to those of the boreal regions 

 to-day, which migrated to the south at that time. Such conditions are to-day 

 favorable for many birds, and in all probability were at that time. Under 

 such circumstances what would prevent the southward extension of such 

 forms as found their favorable conditions moving south? Dixon fur- 

 ther (p. 19) maintains that "the only forms that survived this several 

 times repeated glacial invasion, were those whose pre-glacial breeding 



