. Bulletin of the Michigan Ornithological Club. Michigan Ornithological Club; Birds. 20 Bulletin oi* nut range extended beyond its ; 1 see no reason why the class of birds just mentioned should have been so restricted. Kirtlundi may well be taken as a representative of the class of birds, just referred to. It is a bird which breeds in the northern coniferous /.one. In general, it seems safe to infer that those migratory birds, which now have their breeding grounds in the north^ were among the early migrants which pushed back with the retreat of the ice. Can it be that the eviden
. Bulletin of the Michigan Ornithological Club. Michigan Ornithological Club; Birds. 20 Bulletin oi* nut range extended beyond its ; 1 see no reason why the class of birds just mentioned should have been so restricted. Kirtlundi may well be taken as a representative of the class of birds, just referred to. It is a bird which breeds in the northern coniferous /.one. In general, it seems safe to infer that those migratory birds, which now have their breeding grounds in the north^ were among the early migrants which pushed back with the retreat of the ice. Can it be that the evident northern breeding area of Kirtlandi indicates that it was one of these carlv invaders? And can its. Fig. 3. Lines of Glacial Drainage or Shore Lines. To show rela= tion of those topographic features to bird migration routes. Border of the last ice sheet v Wisconsin), indicated by dashes. apparent adherence to glacial highways indicate that its dispersal dates back to early post-glacial times? Habits of migration may preserve records when fossils are lacking. If tliis was one of the early species to push north, it is but natin-al that it should follow such highways, as it is along such valleys and shore lines, at that time, that the vegetation would make its most rapid extension northward. A comparison of maps (Figures 1 and ?>) is suggestive in this connection. The ma]) of the Prothonotary Warbler (Figure 1) shows the present distribution of a distinctly southern type of bird, which is extending its range northward, and suggests the method and stage which Kirllandi has long ago passed through as it extended its breeding range northward with the amelioration of the glacial climate. These valleys and shores, (Figure .3) as has been mentioned, were in early post- glacial times, as to-day, highways of dispersal. The breeding range of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appe
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