186 PROCEEDINGS OF THE ACADEMY OF 



smallest and darkest, and largest and lightest sets of individuals as yet dis- 

 covered. To prove this I must bring forward the curious variations that 

 ^giothus has sustained in northern North America. 



III. I discovered in Labrador, in 1860, and soon after published a description 

 of, a small Red-poll that I cnW^d fuscescens on account of its color. Specimens 

 had before, however, been collected, and I am inclined to think this form is 

 the one figured by Audubon for the common species ; \mi fuscesctnn is, as far 

 as known, its earliest designation. These Red-polls have since been traced 

 quite across the continent, in British America, to Sitka ; specimens are con- 

 tained in nearly all the collections from the interior. With this extensive 

 range in longitude, the birds' latitudinal dispersion is rather unusually limited. 

 They appear to be mostly confined to boreal America, rarely entering the 

 United States, and then only along its northern border; at least, I have seen 

 no good examples taken further south. Throughout British and Russian 

 America they are liable to be associated with true linarius at any point. In 

 Labrador, however, they are the prevailing, if not the only form. They are 

 also associated in the interior and on the west coast with another "species," 

 to be noticed presently. It is difficult to estimate their numbers relative to 

 those of the two otiier species ; perhaps they are one for ten or twentj-, or even 

 in less proportion. These birds differ from linarius in, 1, smaller size, though 

 this is not very evident except on striking averages ; 2, in relatively and abso- 

 lutely larger, heavier, and wholly blackish bill, furnished with unusually 

 short and sparse jilumules ; 3, in color, which is above dusky, scarcely relieved 

 by lighter streaks, the rump only a trille lighter than the rest of the upper 

 parts, the sides very heavily streaked with dusky, and the red of the male 

 breast intense crimson. 



The form is not to my knowledge found in Europe. Whatever causes have 

 operated to produce this special modification in linarius^ they have not been 

 effective in Europe, and have moreover in America only affected a small per 

 cent, of the total number of individuals. The resulting changes I cannot at- 

 tempt to explain. Besides being not referable to any known general laws, 

 they are in direct opposition to these. Climate, geographical position, &c., 

 should, as we saw so satisfactorily in the case oi cajiescens, have enlarged and 

 blanched these birds, and given them heavier plumules, whereas we have the 

 contrary condition. We might suppose, indeed, that the wide dispersion and 

 irregular movements of the Dusky Red-polls may have interfered with the 

 equable operation of the laws just alluded to, but this does not account for the 

 diametrically opposite result attained. 



The relations of this style to typical linari>is may be briefly exposed. So far 

 as known, it is decidedly more different from the latter than either of the two 

 forms last considered are. Out of several hundred specimens examined, there 

 are a few that cannot be refeired without a query to either species : these are all 

 from the interior of British America, and most of them are immature individu- 

 als. Except in these rare instances, the line between the two kinds is dis- 

 tinctly drawn. There is just a possibility that these dusky birds represent a 

 seasonal eispect of linarius ; but almost everything is against the suggestion. 

 On this supposition, the dusky birds ought to be found, at times, wherever 

 linarixis occurs, — which is not the case, as far as known. Tlie difference in 

 the average size, and particularly in the size and slope of the bill, is not satis- 

 factorily disposed of in this way. 



If I were to venture an hypothesis in this case, I sliould be inclined to frame 

 one looking to such a class of causes, as, for example, that which has operated 

 in the Colorado desert in bleaching birds. As is well known, several birds 

 chiefly confined to that region are paler and grayer than their congeners (con- 

 species?) elsewhere. An influence of this class, working in an opposite direc- 

 tion, may have modified a certain fraction of northern ^giothus, such as 

 character of the forest or shrubbery mainly inhabited by these birds, the 



[Oct. 



