. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 206 Bulletin Museum of Comparative Zoology, Vol. 141, No. 5 Cesar Depression Uppe^ Maranon Xolmis fumigata superspecies X. pernix X. fumigata I RTo Apurimac'^ \^'^^*S&h^ ' ^^^^ Bolivia Fig. 12. Geographical distribution of the Xolmis fumigata superspecies. Xolmis pernix is isolated from the nearest popula- tion of X. fumigata by the Cesar Depression. The Venezuelan isolate of X. fumigata, isolated from Colombian populations by the Rio Torbes Valley, is clearly differentiated morphologically, whereas t
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 206 Bulletin Museum of Comparative Zoology, Vol. 141, No. 5 Cesar Depression Uppe^ Maranon Xolmis fumigata superspecies X. pernix X. fumigata I RTo Apurimac'^ \^'^^*S&h^ ' ^^^^ Bolivia Fig. 12. Geographical distribution of the Xolmis fumigata superspecies. Xolmis pernix is isolated from the nearest popula- tion of X. fumigata by the Cesar Depression. The Venezuelan isolate of X. fumigata, isolated from Colombian populations by the Rio Torbes Valley, is clearly differentiated morphologically, whereas the Peruvian isolates, separated from one another by the Upper Maranon, are not, or are less well marked. X. tuscorufa does not seem to occur northwest of the Rio Apurimac. several occasions" around Quito, Ecuador, but in spite of numerous hours of field \\ ork in apparently suitable habitats around Quito and elsewhere along the Andes, I was never able to even glimpse it. Examination of series of specimens from the entire range of the species revealed that there is practically no geographical variation in size (as measured by wing- length), and only minor variation in color. The only discontinuous variation occurs from Venezuela to northeastern Colombia. Birds from the Andes of Tachira (west of the Rio Torbes Valley), of Merida, and of Trujillo can be considered as an isolate (see Fig. 12) (subspecifically separated as lugubm) distinguishable from other popu- lations of Venezuela and northern Colom- bia by having the crissum ochraceous instead of sooty and concolor with the rest of the underparts. I suppose that the transition from ochraceous to dark sooty brown takes place across the dry valley of the Rio Torbes (see Fig. 12), an important barrier for Andean species, as I pointed out elsewhere (Vuilleumier, 1969a, 1969b). The birds from southern Ecuador and northern and central Peru appear to be geographical!)' isolated from one another by the valley of the upper Rio Maran
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