294 COLAPTES MEXICANUS, RED-SHAFTED WOODPECKER. 



Mr. J. H. Batty tells rae of a New Jersey specimen, got a few years since, with mixed 

 red and black cheek patches. As C. mexioanus never occurs in these regions, hybridity 

 is there impossible; and the fact is demonstrated that C anratus may thus tend toward 

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

 influences. The important bearing of this fact cannot easily be over-estimated ; the 

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



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

 into question by Mr. Allen. Tliis writer says (p. 110): " Few congeneric species, it 

 would seem, need be more distinct than Colaptes aura'ns and C. mexkamia, 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 which 

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

 shade off gradually on the one side into C. auratiis, and on the other into ('.mexieanus ; 

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

 distance of several hundred miles ; while to the southwt^tward is a smaller synthetic 

 race (C. chrysmdes) partaking mainly of the characters CF; C. auraliiK. When but com- 

 paratively few insta^nces were known, in which specimens combined in various degrees 

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

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

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

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

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

 with the demonstrable evidence of the power of climatic influence, seems to furnish 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 tlio line of junction of the respective habitats of two 

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

 the forms in question. Bnt the real objection to the theory— granting the possil,ility of 

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

 difterent forms occur also at differeiit points in latitude, between which each successive 

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

 supposed to account for the gradual change. Furthermore, a differentiation is now 

 icnoNvn 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 given 

 character under certain specitio climatic conditions. If the theory of hybridity ho urged 

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

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

 has to support: and yet there seems to be little butter evidence in its behalf in cases 

 where the intergrading forms happen to be difl'erently situated in respect to longitude." 



For my own part, I am strongly inclined to endorse this view, though I do not d-ny 

 thiit there is much to be said against it. No weak argument, indeed, is comprehended 

 in the statement, that if C. auratiis and mexieanus 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 moditicatiou 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 Splujraineus variiis and ruber — it is merely pushed tu a further extreme, and appeals 

 in stronger light, because of the greater amount of differentiation snffered. Such being 

 my view, I may be justly accused of incon.sistency in not formally reducing C. mexieanus 

 to C. anratus var. mexieanus ; and I would say, that such an action may yet be deemed 

 advisable, or even prove necessary. But our nomenclature is merely a matter of con- 

 venience, of little more significance than the index of a book ; the present case is 

 unique in some respects; and, especially, the hypothesis of hybridity is not yet actually 

 disproven. 



lu Xortbern Dakota, beyoDd tbe Missouri water-sbed, the true C. 

 anratus occurs, without the slightest admixture of mexieanus, at least 

 lour hundred miles west of the iled Eiver — much further west than the 

 point on, the Missouri region where the gradation commences, ^^ hi/bridus^' 

 having been noted even from Kansas, and being the pievailing Missouri 

 form. 



COLAPTES MEXIOANUS, Sw. 



Bed-shafted Woodpecker; Mexican Flicker. 



Pious cafei; Gm., Svst. Nat.i,.ltd6, 431 — LAiHy Ind^,Qrn. ii, 1790, 242 (supposed to be 

 from Cape of Good/S9'fi%ea JbyM/C/tlSO/?® ' ' ^ vi 



