294 COLAPTES MEXICANUS, RED-SHAFTED WOODPECKER. 



Mr. J. H. Batty tells me of a Neio Jerseif speciraeu, got a few years since, with mixed 

 red and black check patches. As C. mexironus never occurs in these regions, hybridity 

 is there impossible ; and the fiict is demonstrated that C. aiirdtiifi may tliiis tend toward 

 the characters mcxicanufi by its own inherent susceptibility to change under climatic 

 inflneuces. The important bearing of this fact cannot easily be over-estinvited ; the 

 circumstance is, in my judgment, strongly against the theory of hybridization. 



So far as I am aware, the assumed case of C. ^'hiihridits" was first called seriously 

 into que.stion by Mr. Allen. Tliis writer says (p. IIS): " Few congeneric species, it 

 would seem, need be more distinct than Colaptes aniatv^ and C. mexiccuiufi, the one 

 occupying the eastern and the other the western side of the continent. Yet a mixed 

 race has been long known to exist in the region where their habitats adjoin, in wliich 

 every possible combination of the characters of the two birds is presented, and which 

 shade off gradually on the one side into C. anratns, and on the other into C. mcxicavun ; 

 these, as it were, engrafted characters not entirely fading out in either direction for a 

 distance of several hundred miles ; while to the southwestward is a smaller synthetic 

 race (C chrymicle^) partaking mainly of the characters o C. anraliis. When but com- 

 paratively few instances were known, in which specimens combined in various degrees 

 the characters of two (piite distinct species, their synthetic character was generally 

 explained by the theory of hybridity ; but the irrefragibility of the evidence now at 

 hand in proof of the gradual intergradation of such forms over large areas — the 

 transition being so gradual as to occupy hundreds of miles in the passage — and also 

 coincident with a similarly gradual change in tlie conditions of environment, together 

 with the demonstrable evidence of the power of clin^.atic inlluence, seems to fuinish a 

 far more satisfactory explanation of these perplexing phenomena. But an advocate of 

 the theory of hybridity might still assume that this gradual transition over a wide 

 area is no objection to the theory, since the gradual fading out of the impression of 

 contact in either direction from the line of junction of the respective habitats of two 

 forms is just the result that would be anticipated from such a sexual intermingling of 

 the forms in question. But the real objection to the theory— granting tlie possiltility of 

 hybridization on such a gigantic scale, wliich seems really improbable — is, that widely 

 dilx'erent forms occur also at ditfercnt points in latitude, between which each successive 

 stage of gradual differentiation can be readily traced, where hybridity can scarcely be 

 suiTposed to account for the gradual change. Furthermore, a dilferentiation is now 

 known in so many cases that it amounts to the demonstration of climatic variation as 

 a general law, by means of which a species may be safely predicted to take on a givea 

 character under certain specific climatic conditions. If the theory of hybridity be urged 

 to account for the intergradation of forms occurring at localities differently situated in 

 respect to latitude, as has been sometimes done, it evidently fiiUs under the weight ic 

 has to suxiport: and yet there seems to be little better evidence in its behalf in cases 

 where the intergrading forms happen to be differently situated in respect to longitude." 



For my own part, 1 am stronglj' inclined to endorse this view, though I do not d; ny 

 that there is much to be said against it. No weak argument, indeed, is eomjirehended 

 in the statement, that if C. aurufiis and mcxlcauus are not " good species," then there are 

 none such in ornithology. But I would reply, as I did on a former occasion, that it is 

 only in virtue of missing links that we are enabled to predicate species in any case. If 

 all the steps in a line of descent with modification were before our eyes, we could no 

 more draw specific, or generic, or ordinal lines of distinction, than we could say where 

 a circle begins. This particular case of Colaptes seems to be exactly parallel with that 

 of Splu/rapiciis rariufi and ruber — it is merely pushed to a further extreme, and appeals 

 ii' stronger light, because of the greater amount of differentiation sulYt>red. Such being 

 my view, I may be justly accused of inconsistency in not formally reducing (). mexkaiius 

 to C. (iiiratus var. mexicanitu ; and I would say, that such an action may yet be deemed 

 advisable, or even prove necessary. But our uomenclature is merely a matter of cou- 

 venieuce, of little more siguificance than the index of a book; thi^ present case is 

 uni(iue in some respects; and, especially, the hypothesis of hybridity is not yet actually 

 disproveu. 



In Nortbern Dakota, beyond tbe Missouri water-sbed, tlie true C. 

 aiiratus occurs, witbout the sbjj;btest admixture of mexicanus, at least 

 four hundred miles west of the Ked River — mucli further west than tbe 

 ])()int on tbe Missouri region where tbe gradation eominenees, '■^hiihridus" 

 liaving been noted even from Kansas, and being tbe prevailing Missouri 

 form. 



COLAPTES MEXICANUS, Sw. 

 Red-shafted AVoodpecker ; Mexican Flicker. 



Picus cafer, G.M., Syst. Nat. i, ll^A, 4:?!.— L.vTii., Ind. Orn. ii, 1790, 242 (supposed to be 

 from Cape of Good Hope). 



