November 3, 1905.] 



SCIENCE. 



553 



species of bird ever breed in the same region. It 

 is, of course, by no means unusual for two forms 

 subspecifically isolated to occur together during 

 migration or in their winter homes. 



If I understand your fourth question rightly I 

 should say that there are a good many known 

 cases of species more closely related to one an- 

 other than to other species occurring (in breeding) 

 in the same region. The best examples of this 

 that occur to me are the Allen and Least fly- 

 catchers, the blue->vinged and the golden-winged 

 warblers (these two species interbreed fairly and 

 their hybrid offspring is fertile), and the Swain- 

 son's and Bicknell's thrushes. All these breed 

 in New England and the species mentioned in 

 pairs breed to the same covers. I think that in 

 England excellent examples may be found among 

 the very closely isolated warblers belonging to the 

 family Turdidse and the family Sylviinee. 



I certainly should be loath to believe that two 

 birds which were subspecies of the same species 

 could breed, at least in the same area. 



C. HART MERRIAM. 



Your letter making inquiries as to coextensive 

 ranges of subspecies of the same species, and so 

 on, reached me some little time ago, but owing 

 to pressure of other matters I have not been able 

 to reply earlier. My answer to questions 1, 2 and 

 3 was no, from the first. I felt a little uncertain 

 about the fourth question, and have spent some 

 time in running over lists of birds and mammals 

 in order not to make a mistake. After careful 

 consideration I must answer this question in the 

 same way as the others, as I fail to find any two 

 closely related species inhabiting exactly the same 

 region. 



JOSEPH GRINNELL. 



In reply to your recent circular, I offer the 

 following : 



In birds several subspecies may occur in the 

 same region in tointer, because of their seasonal 

 scattering. But I know of not even one case 

 where two subspecies breed in precisely the same 

 region. I have run down two alleged cases — both 

 proved irrelevant. 



My criterion for diagnosis as subspecies is — 

 two forms connected by a continuous series of 

 intergrades uninterruptedly covering the interly- 

 ing ground. If a geographic hiatus exists (as 

 in island races), even though intermediates may 

 apparently bridge over the difference in mean 

 characters, I call the two forms species. . I can 

 see no difference between species and subspecies, 

 except an average one in degree of differentiation; 



and that fluctuates with personal opinion (e. g., 

 note A. O. U. rulings from year to year ! ) . I am 

 about ready to deny the value of trinomials in 

 nomenclature on this account. Call all distin- 

 guishable groups of individuals species, as Sharpe 

 tries to do in his ' Hand-List of Birds.' I know 

 of no case where two species inhabiting the same 

 region are ' closely ' related, or even more closely 

 related than any other species is to either one. 



I believe in isolation either by barriers, or by 

 sufficient distance to more than counterbalance 

 invading inheritance from the opposite extreme 

 (geographically) as being one essential factor in 

 the differentiation of species. 



LEVERETT MILLS LOOMIS. 



1, 2. I know of no instance. 



3. No. 



4. I do not recall a case among the Tubinares, 

 particularly in the closely related species in 

 Oceanodroma, Puffinus, Motrelata; of course ' ex- 

 actly the same region ' in these birds would be the 

 breeding grounds. 



CHARLES H. GILBERT. 



In attempting to reply to your circular letter 

 concerning subspecies, I am limited by the fact 

 that well marked subspecies are hardly known in 

 ichthyology. Unless the term shall be finally ap- 

 plied to such local forms as the fresh-water 

 sticklebacks, or to the minutely variant form char- 

 acteristic of different tributaries of the same 

 hydrographic basin, I see no probability of the 

 subdivisions of fishes beyond the species. I can 

 not answer your questions, therefore, on the basis 

 of personal experience with subspecies, a fact 

 which prevents my views from having any weight. 

 I may, however, venture the following suggestions: 



The answer to all your questions will depend 

 upon the definition given the terms ' range ' and 

 ' region.' It might well be found, for example, 

 that two subspecies of song sparrow would occupy 

 the Santa Clara Valley, one confined to the tule 

 swamps, the other to the dry uplands. That two 

 subspecies should have coextensive range and live 

 in the same habitat within the range, would seem 

 impossible from the accepted definition of sub- 

 species. I refer here to the older definition of 

 subspecies, for many well known zoologists have 

 recently adopted the view that subspecies are 

 determined by the small amount of divergence' 

 rather than the ascertained fact of intergradation. 

 To those who so hold, anything would be possible 

 with subspecies which would be possible with 

 species. 



