An Ornithological Comedy of Errors: Catharus occidentalis and C. Frantzii

Abstract

Anyone who has critically identified thousands of birds in museums has surely found a number of misidentifications and added his share, but these are mainly at the subspecific level. Errors at the specific level are less common, and the case presented here is unique in my experience-the only one where a bird's. supposed geographic variation is actually based, to a significant degree, on specimens of another species! For years contradictory and irreconcilable statements about Catharus haye plagued us. Controversy has raged about the birds. of Omiltemi, Guerrero, Mexico, whence Ridgway long ago (1907) recognized two sym-patric species; one of the forms involved he had named C. /rantzii omil-temensis. Soon after Hellmayr (1934) had questioned Ridgway's judgment , Griscom (1937) reaffirmed and strengthened it, pointing out that "the real, fundamental specific characters. .. are (1) the wholly yellow mandible in/rantzii, whereas the terminal half of the mandible. is blackish in occidentalis; (2) the inner webs of the bases of the remiges in occiden-talis are abruptly buffy, forming a distinct buffy patch at the base of the spread wing, which is otherwise grayish on the under surface. These differences are much less pronounced in immature specimens." Later I (Phillips, 1962a: 362-364) added minor characters useful in Jalisco, where I had discovered C. /rantzii and collected both species together. Finally, Rowley discovered important differences in their biology (Rowley and Orr, 1964). Meanwhile unfortunate errors by Ridgway himself had started the idea that only one variable species is involved. A mixed series. identified (in some cases erroneously) as C. occidentalis in the U.S. National Museum led Hellmayr (1934: 468) to synonymize o.miltemensis because he had "before me three topotypes from Omilteme collected by Nelson and Gold-man in May, 1903-one of them, an adult female, shot on the same day (May 19) as the type-which differ nowise from Jalisco specimens. The buffy basis [sic] to the inner web of the remiges, upon whose absence 605 The Auk, 86: 605-623. October, 1969