226 APPENDIX TO OSCINES. 



the Titlark, Green Black-capped Warbler, Lincoln's Finch, and Whito-crowned Spar- 

 row ; next, a Hudsouiaa belt, extending from 500 to 1,000 feet below the timber-line, 

 ju which may be found sub-alpine plants and such birds as the Canada Jay, Audubon's 

 Warbler, Brown Creeper, &c. ; then, of varying extent, a Canadian zone; below this, 

 an Alleghenian ; and, finally, on the plains, a Carolinian. It is quite impossible to fix 

 any precise limits to these various fannte, however; tbey pass mto each other fjuite 

 gradually, aud extend to such diflerent elevations, according to the diiierent influences 

 to which they are exposed, that sometimes two of them -^ill be side by side for some 

 distance through the same altitudes, with merely a ridge intervening. 



Kevertheless, the temperature of a region, although it modifies the plant and insect 

 life to a great extent, determines entirely the range of birds. Junco hyeinaUs abounds 

 on the plains and up to 8,000 feet during winter, yet, iu company with three of the 

 other four varieties that spend the winter in the same localities, it migrates to the 

 ■north on the approach of the breeding season, while J. caniceps alone ascends the 

 mountains, and finds the requisite climate in the higher forests, which the others seek 

 at higher latitudes. Yet it is well known that the Snow-bird breeds in the AUeghanies 

 further south than this region ; and there appears no obvious reason for a northern 

 migration, when it could easdy find any desired temperature by ascending the mount- 

 ains in company with its congener, J. caniceps. On arriving ftrom the north, most 

 birds appear among the foot-hills and along the edge of the plains, some days in ad- 

 vance of their arrival higher up in the mountains; and the same thing occurs during 

 the vernal migrations, showing that most of the species prefer migrating along the 

 edge of the plains rather than through the mountains. Even so northern a species as 

 Ampelis (jarrulus, which, during midwinter, is rare among the foot-hills, frequently 

 gathers there in large flocks, iu spring, preparatory to its leaving the country. The 

 boundary between j)lains and mountains appears to be a highway for all the migratory 

 species iu spring and autumn. 



The most prominent characteristic of the avi-fauna of this region — which may be 

 taken as a fair type of the Eocky Mountain chain between the thirty-eighth and forty- 

 first parallels — is, perhaps, the remarkable number of birds which are represented 

 'further east by very closely-allied races or species. Of these there are over twenty ; 

 and whll<; some are plainl;^ varieties shading into the eastern forms by such imper- 

 ceptible gradations as to leave no doubt of their specific identity, others cannot be so 

 •summarily disposed- of. No one has shown, for instance, that Gcothlijpis macrjillirrayi 

 is connected by gradual, intermediate stages, with G. pkiladclplua ; or that Junco cani- 

 ceps is .similarly related to the other forms of its genus. But are we to accept this 

 ■definition of a species ? Are only such forms entitled to specific rank which cannot 

 be shown to intergrade with others? The tendency of the day is decidedly in that 

 direction; yet, if logically carried out, this system will eventually lead to startling 

 results. It Pipilo erythroplithalmus can be shown to gradually pass into P. arcticus to- 

 ward the Rocky Mountains, and into P. allcni in Florida ; and if the former changes 

 into nrcf/oiiHs aud megaJonyx on the Pacific coast, and thus all these forms are to consti- 

 tute a single species, what reason is there for still keeping apart the various races of 

 Colaptcs, which intergrade quite as closely ? Carpodacus cassini is considered a good 

 species; yet its points of ditference from C. purptireiis are fewer aud less marked than 

 those sejiarating Contopus vircns and C. richarilsonii, which are now thiown together 

 under the same specific name. New links and new intermediate forms are constantly 

 coming to light ; and if, on discovering the gradation between any two forms previ- 

 ously held as good species, we are at liberty to combine them as races of the same 

 species, will it not be equally proper to combine other forms together, even though 

 some of the intervening links are wanting, where analogy and experience point to that 

 conclusion ? It is the exact reverse of Brehm's system, which ]^d that ornithologist to 

 find no cud of species, where others could see but one. 



The results of this system of reasoniug.are already beginning to manifest themselves. 

 Different forms are thrown together with the utmost freedom, and we are learnedly 

 ■referred to "well-known laws" of geographic aud climatic variation. Yet there are 

 cases where these "laws'' will not work at all, and then they are quietly ignored. In 

 the Rocky Mountains, for example, a species of Wren is found, so well marked in its 

 notes, plumage, and habits, that the older ornithologists considered it quite distinct : 

 but being somewhat like the eastern House Wren, only grayer and paler, it is at once 

 referred to that species, and its changed color accounted for by the "law" that, iu this 

 region, the dry air and bright sunlight exercise a bleaching inlluence. In the same 

 locality, and existing under precisely similar physical conditions, is a species of Fly- 

 catcher, also supposed by Audubon and the older school to be a distinct species, but 

 which these modern ornithologists pronounce to be " var." richardsoiii of the eastern 

 Wood Pewee. Unfortunately, in this case, the bird happens to be darker than its east- 

 ern relative, and so we have not a word concerning the " laws of climatic variation" 

 and the "mean amount of rain-fall." Nor do the chief exponents of this new method 

 of reasoning find any limits to their course when once fairly started. In a review of 

 a certain genus of the Tyrannidce {Myiarchm), one of our present writers has declared 



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