138 Bulletin American Museum of Natural History. [Vol. XXXVI, 



on the Pacific slope of the Andes, and, on the Atlantic slope, to eastern 

 Bolivia, where Miller and Boyle found its southern end between the Yungas 

 of Cochabamba and the mountains above Santa Cruz. 



Throughout approximately 2500 miles of its length, that is, from Vene- 

 zuela to Bolivia, the bird-life of this zone is so remarkably uniform in charac- 

 ter that, as with the Amazonian and Orinocan elements in the Colombia 

 fauna, one cannot arbitrarily segregate any part of it and study it satisfac- 

 torily to the exclusion of the rest. 



Our field work is now chiefly directed toward the acquisition of adequate 

 collections of the birds and mammals of this exceptionally interesting zone 

 of life, and until our work is completed, it will be impossible to speak of the 

 zone as a whole or of its altitudinal boundaries outside of Colombia. A 

 study of the northward extension of the Subtropical Zone into Costa Rica 

 reveals what may be termed a ' zoological fault' in Panama, while a compari- 

 son of the Costa Rican representatives of Colombian species with those 

 recorded from the Santa Marta group gives some significant results which 

 will be presented later. 



Data are unfortunately lacking for a satisfactory comparison of the 

 Subtropical Zone bird-life of the Andes with that of the mountains of south- 

 ern Venezuela, the Guianas, and southeastern Brazil. 



The birds of the Subtropical Zone, as might he expected, are almost 

 exclusively forest-dwellers; the Green Jay {Xanihourd) is found about 

 forest-borders and is one of the few Subtropical species inhabiting semi- 

 arid places. The Dipper {Cinclus) and Torrent Duck (Merganetta) , while 

 confined to mountain streams, do not require that the shores be forested. 

 But exceptions of this kind are rare. Tanagers are the most numerous in 

 species as well as in individuals, the family Tanagridse being the only one 

 which, in Colombia, has more species in the Subtropical Zone than in the 

 Tropical Zone. The Thrushes, while far less numerous in species, have 

 almost as large a proportionate representation. Guans, Trogons, Capites, 

 Toucans, Dendrocolaptids, Cotingas and Wrens are all characteristic of 

 the Subtropical Zone and, in the Colombian Andes, have about half as 

 many species in it as in the Tropical Zone. The Flycatchers are about 

 one-half as numerous in the sub tropics as in the tropics. Families of forest- 

 inhabiting Tropical Zone birds which have a comparatively poor representa- 

 tion in the Subtropical Zone ^ are the Pigeons, Parrots, Woodpeckers and 

 Orioles, of which there are about four times as many species in the tropics 

 as in the subtropics, and Formicarians, of which we found only seventeen 



1 It should be understood that these statements refer only to the results obtained by us in the 

 Colombian Andes. 



