MicHiGAx Ornithological Club 



17 



by which the present species has found its way to its present breeding area 

 since the Ice Age. From this point of \'iew stragglers have more than usual 

 interest, ikot because they are i-ai-c, but because they show the possibilities 

 oi tuture lines of dispersal and show how dispersal qy extension of the 

 breeding range of a s])ecics is taking place at the present time. Of course 

 tnis does not apply to all stragglers into any region, but it is especially 

 suggestive in the case of birds which normally breed along a highway 

 south of the region invaded by the stragglers. 



Fig. 2. Probable migration route of Kirtland's Warbler. Arrows 

 indicate location of records and broken lines probable 

 routes. 



The paths or liiglnvays by which it seems that the Prothonotary Warb- 

 lers (and also many other animals) have invaded Michigan, thus seem 

 to be as follows : Those in the southwestern part of the State have pushed 

 up from the Kankakee swamps of northern Indiana to the St. Joseph river 

 and then have spread along its course and over southwestern Michigan. 

 These birds may have reached the Kankakee swamps either by the Illinois 

 or Wabash river bottoms, or both, as has been mentioned. The birds of 

 southeastern Michigan and northwestern Ohio, via the Upper Wabash and 

 extinct lake bottoms bordering Lake Erie. 



Let us now consider the bearing which, these facts have upon the dis- 

 tribution of Kirtland's Warbler. When comparing the distribution of these 

 two birds one must not press the analogy too close, but must be contcntj 

 with general resemblances. But if the general principles or resemblances 



