68 THE AMERICAN NATURALIST, [VoL. XXXIII. 
place, is less frequented by amateur ornithologists than probably any 
other part of eastern North America; the inference then is pretty 
plain that if we had more of the right kind of amateurs we should 
probably also have more facts with which to answer the question — 
where does this bird summer, and where lies its exact migration 
route? 
The importance of this question is very great, for, seemingly at 
least, the distribution of this warbler suggests a migration route 
almost unique. Yet, if we accept as our working theory of migration 
-the only rational one which has been offered to the present day, z7z., 
Palmén’s, that the annual migration route of a species indicates the 
way by which it originally immigrated into its present breeding home, 
how are we going to explain the apparent uniqueness of the route of 
Dendroica kirtlandi? It must not be forgotten that it is extremely 
difficult, if not impossible, to trace the individual migration paths of 
a homogeneous species covering a large area and occupying a multi- 
tude of routes between its vast summer habitat and its equally exten- 
sive winter quarters, and that, even in cases where the birds of a 
widely distributed species have evolved slightly differentiated forms 
traveling on their own migration routes, it requires the keenest power 
of discernment in the sharpest bird expert to trace these routes. 
How can we tell but that many of the homogeneous species occupy- 
ing the whole area of eastern North America do not in part follow 
a route similar to that of Kirtland’s warbler? It will now be seen 
how desirable it is to trace step by step the progress of this species 
from the Bahamas to Michigan, and possibly beyond. Here is a 
species so very strongly differentiated as not to be mistaken for any 
other, and so limited in numbers that it probably follows only a single 
narrowly limited route. When we shall have solved this problem we 
shall also know a good deal more about the road by which in past 
ages part of our fauna entered their present habitat. 
There remain only a few words to be said about the illustrations 
in Mr. Butler’s book. None, as far as I have discovered, are new, 
and they would have received no special mention had the selection 
been good in all cases. We notice with pleasure all the character- 
istic and accurate bird portraits from John L. Ridgway’s pen, fur- 
nished by Dr. Merriam’s division in the Department of Agriculture, 
but we must earnestly protest against the presence of a number of 
antique caricatures — borrowed, it is true, from a book which still 
periodically appears in the market — which neither illustrate, because 
it is eure in most of them to recognize the birds they are 
