^°8c)f ] ^WKT>?, on the Hudsontan Chickadee and its Allies. 327 



as the Rocky Mountain form. We may cite as illustrating this 

 plan of racial distribution in Boreal and Arctic America, Picoides 

 a?nericanus with its subspecies alascensis and dorsalis, and 

 Acanthis llnaria with subspecies holbcelli and rostrata. One 

 of the tables appended to this paper will show their parallel 

 differentiation with the Hud sonian Chickadees. In the same 

 table I also include certain forms of the Rock Ptarmigan 

 {Lagofus rupestris") and the Horned Larks {Otocoris alpes- 

 tris), whose habitats and manner of differentiation have the same 

 correlation with those preceding. Of course the di.stribution of 

 the Ptarmigans and Horned Larks is, in the first case, more 

 arctic, and in the second, more continental than that of the other 

 three species given, but, considered solely with reference to their 

 boreal distribution, there is more than an ordinary resemblance 

 among them all in spite of the marked differences in their habits. 



Owing to the comparative scarcity of summer specimens in the 

 series, I have based all important comparisons on skins secured 

 after the fall moult and before the breeding season, viz., between 

 the fifth of August and the first of May. It would have been 

 preferable to limit these comparisons either to fall or early spring 

 birds but the series was too small to justify it. As in other species 

 of the genus, there seem to be no differences between the sexes 

 of this Titmouse, either in size or color, and I have consequently 

 considered the adults of both sexes as equally representative of 

 the characters ascribed to the species or subspecies under which 

 they are classed. 



Seasonal color phases in the Parzts hudsonicus group are so 

 slight and simple, being chiefly the result of summer bleaching 

 and abrasion, it is easy to make due allowance for such differences 

 when determinations were necessarily made from breeding speci- 

 mens. The plumage of the young is too poorly represented to 

 warrant special mention. 



I. Parus hudsonicus Forst. Hudsonian Chickadee. 



Habitat. — All of southeastern British America, except north- 

 ern Labrador and Newfoundland, from Lake Athabasca and the 

 Nelson River south to mountains of northeastern Minnesota, 

 northern Wisconsin, Michigan, New York, Maine, New 

 Hampshire, Vermont and Massachusetts. 



