1917.] Chapman, Distribution of Bird-life in Colombia. 139 



species in the sub tropics as compared with eighty-two in the tropics. Many 



species of this last-named group, it is true, are scrub haunters, nevertheless, 



' their abundance in heavy tropical forests is shown by the fact that Miller 



secured twenty-four species in the Amazonian Fauna in a month's collecting. 



As might be expected, few true Finches inhabit the Subtropical Zone, 

 but the Tanager-Finches of the genus Atlapetes are almost restricted to it. 

 The Bucconidse are represented by the only one of the eighteen tropical 

 species which ranges upward to the subtropics; the Motmots by but one, 

 whUe the Galbuhdte appear to be wholly absent. 



Satisfactory data are wanting for a study of the origin of the bird-life 

 of the Subtropical Zone. Our work in Colombia merely touched a portion 

 of the vast area in which field studies and' carefully labeled collections must 

 be made before one can treat of the zone as a whole, and, as before stated, 

 its life is too uniform to permit of conclusions being based on the study of a 

 part. 



It appears, however, that so far as birds are concerned, the Tropical 

 Zone differs from the Temperate and Paramo Zones in two important 

 respects — one of which is the corollary of the other. First, the Subtropical 

 Zone, latitudinally, does not extend beyond the limits of the Tropical Zone 

 with which, when altitude permits, from Bolivia to Mexico, it is practically 

 coterminous. Second, the Subtropical Zone, as a faunal area, does not 

 descend to sea-level. Consequently it follows that the Subtropical Zone 

 is always an altitudinal zone, and it also follows that its life, as a whole, 

 was derived from the tropics. 



To what extent the altitude of the Subtropical Zone is affected by lati- 

 tude, I am not as yet prepared to say. Brachyspiza capensis peruviana, a 

 species of the Subtropical and Temperate Zones, is found at sea- level on the 

 Island of Curasao. It descends the Rio Negro east of Bogota to Quetame 

 (alt. 4500 ft.) but was wanting at Buena Vista. It, however, occurs at 

 Caicara on the Orinoco. This species is really most characteristic of the 

 Temperate Zone, but is also common in the arid subtropics. Its further 

 descent to the Tropical Zone forms, therefore, an exception to the rule that 

 the life of any zone is derived from a lower level. 



Assuming that species found in all three ranges must have had a com- 

 mon point of origin south of the latitude where these ranges leave the 

 Ecuadorian Andes, it is interesting to ascertain the results following their 

 isolation. In most instances when there is appreciable racial variation, 

 two races develop, one of which is found in the East Andean Fauna, the 

 other in the West Andean Fauna. Where only one race is evolved it is 

 generally found in the East Andean Fauna, while the West Andean form 

 resembles that inhabiting western Ecuador. In some few instances the 



