126 PROCEEDINGS OF THE ACADEMY OF 



are hastily prepared by persons of little skill in such matters, and are more or 

 less deteriorated by packing and transportation. 



The first question upon which we propose to treat is the line to be drawn 

 distinguishing " species " from " varieties." I do not, however, intend to dis- 

 cuss at any length this difficult and perplexing point, but only as it touches 

 more directly upon the birds to be noticed, and in the case of several of them 

 it may possibly well be left (as the matter now stands) entirely to one's dis- 

 crimination, whether he is to regard them as valid "species" or subordinate 

 " varieties." 



Now we must and do admit a certain extent of variation, influenced by dif- 

 ferent agencies, as age, season, and locality, when the cause of such variations 

 can be thus satisfactorily explained. It does not follow, however, that, be- 

 cause we have a series connecting by a gradual transition two extremes, we 

 are to consider the whole as one species, the discrepancies indicating different 

 varieties. The difference between these extreme examples is often too great 

 to admit of this ; and when we have traced a species through all its variations 

 to a certain point where the discrepancy from the typical style is too great 

 and uniform to be accounted for by any physical cause, it becomes us as nat- 

 uralists to assign to such extreme conditions a specific rank. What more 

 can we do ? and what is more in accordance with the laws of nature ? There- 

 fore we cannot do better than to accept as valid these representative forms, 

 when they can be assigned distinctive habitats; and where they are substan- 

 tiated by a sufficiency of specimens, to such we may allow a reasonable ex- 

 tent of vuriation, not, however, beyond the limit controlled by physical 

 causes. 



We find that in all cases where individuals occur which apparently connect 

 the approaching extremes of two well defined representative forms, that such 

 are almost always from localities inhabited by each, or from the region where 

 their respective habitats overlap. It is under such circumstances that we 

 must a.dm[t ht/bridization among birds, and abundant evidence can be adduced 

 that such hydridization does occur between congeneric species, and that it is 

 not only occasional but general ; indeed an instance will hardly be found 

 where, by collecting in the region where an eastern species and its western 

 representative are found together, the collector will not obtain hybrid speci- 

 mens. Such has been the case with myself respecting several species, as well 

 as with nearly all others who have made ornithological collections in the 

 West. 



What more conclusive evidence of hybridization need we have than an ex- 

 amination of the numerous examples of such a condition of Colaptes from the 

 upper Missouri region, where the ranges of eastern C. auratus and western C. 

 mexicanus adjoin. In this instance we have specimens showing as gradual 

 transition between the two extremes as in any other instance where hybridi- 

 zation is usually less evident, because the species are more obscurely colored 

 and the pattern less sharply defined. If we are to consider the C. auraius as 

 one extreme of a single species, the C. mexicanus^ its representative of the op- 

 posite side of the continent, the other, Colaptes chrysoides, another " sport," and 

 the hybrid specimens from intervening ground the connecting links, all 

 merely variations accruing from changes that might be wrought by longitudi- 

 nal distribution, etc., we may as well give up the idea of species in birds, and 

 in fact their study in detail entirely. 



Besides the case of Colaptes we have other abundant proof of hybridization 

 in specimens which combine the character of an eastern species and its west- 

 ern representative, or two closely allied species, or even two of different gen- 

 era. Of this category I may mention the following couplets, which are repre- 

 sented in individuals in the Smithsonian collection : Fims villosus and 1'. har- 

 riiii — P. pubescens and P. gairdneri — Sphyrapicus ruber and S. nuchalis — 

 Chrysomiiris mexicana and C. psaltria — Zonotrichia leucophrys and Z. gambelli 

 — Junco oregonus and J . caniceps — J. oregonus and J. hycmalin — I'ipilo ery- 

 throphthalmus and F. arcticus — Agelaius phoeniceus and A. gubernator — Stur- 



[June, 



