238 Bent, Variation in Black-throated Loons. |.April 



GEOGRAPHICAL VARIATION IN THE BLACK- 

 THROATED LOONS. 



BY A. C. BENT. 



Dr. Jonathan Dwight's interesting paper in 'The Auk' for 

 April, 1918, describing a new species of Loon from northeastern 

 Siberia, has opened up a subject to which I have given considerable 

 study without having been able to come to any satisfactory conclu- 

 sion. After examining directly or indirectly some seventy speci- 

 mens of Black-throated Loons, including the entire series in several 

 of the largest collections in this country, I came to the conclusion 

 that the necessary material was still lacking to settle satisfactorily 

 the true status of this group. 



I have long recognized the existence of a large, Green-throated 

 Loon in the Bering Sea region; but I have postponed publishing 

 anything on it until I could obtain enough breeding birds from 

 somewhere in that region, to establish a more or less definite breed- 

 ing range in which a more or less constant form is to be found. 

 Now that Dr. Dwight has seen fit to open up the subject, I feel 

 called upon to publish what incomplete data I have on the whole 

 group. 



It seems to me that there are only two alternative theories into 

 which the known facts may be made to fit. The first and most 

 likely theory is that there is but one circumpolar species, divided 

 into three, or possibly four, subspecies, as hereinafter designated. 

 To support this theory we need more material from Siberia and 

 eastern Europe to show complete intergradation between the two 

 intermediate subspecies, arctica and suschkini, though Avhat material 

 we have seems to indicate that such intergradation exists. An 

 argument against this theory is the fact that the two extreme sub- 

 species, viridigularis and pacifica, apparently breed side by side 

 in northeastern Siberia and northwestern Alaska. 



The second theory is that there are two species, arctica in Europe, 

 with viridigvlaris as a Siberian subspecies occupying a subarctic 

 area, and pacifica in North America, with suschkini as a Siberian 

 subspecies occupying the Arctic coast. This theory would explain 



