104 Annals of the Carnegie Museum. 



have already been developed. Probably its peculiarities and char- 

 acteristics may entitle it to rank as a distinct faunal area. 



The Subtropical Zone is entirely a humid forest association, and 

 its bird-life is therefore of a more uniform character than that of the 

 Tropical. Its lower altitudinal limit depends primarily upon the level 

 of atmospheric condensation, which is ordinarily about 4.500 feet, 

 but may be much lower as a result of local conditions, while its upper 

 boundary is at an elevation of approximately 9,000 feet. Where forest 

 is absent this zone, as such, is omitted, its place being taken by the 

 zones immediately above and below respectively, certain species of 

 each extending their usual range to fill the gap. In the Santa Marta 

 region the Subtropical Zone, while entirely homogeneous, is much re- 

 duced, so far as number of species is concerned, when compared with 

 adjacent regions. A careful analysis and comparison of its fauna 

 discloses the fact that it has little directly to do with the same zone 

 as it exists in the Eastern Andes, but is in fact very closely related to 

 the Subtropical Zone of the Venezuelan Andes and coast range. This 

 close relationship implies that the Sierra Nevada must once have 

 been joined with these latter ranges, and that the connection has since 

 been interrupted. The indications are that the Dutch West Indies 

 and other islands along the coast are the remnants of this submerged 

 and broken down mountain chain, which once sufficed to carry the 

 fauna of the Subtropical Zone into the Sierra Nevada from farther 

 east. From the comparatively small number of Subtropical forms 

 occurring in the Sierra Nevada we infer that the range in question 

 must have stood at the western extremity of the original chain, and 

 that its fauna must have been derived almost entirely by latitudinal 

 extension, since we find that by far the larger part of the Subtropical 

 forms are more or less closely related to those of the Venezuelan 

 Andes, and more remotely to those of the Eastern Andes of Colombia. 

 Unfortunately we do not know just when the coast chain of moun- 

 tains was broken up ; could this be determined, we would have a 

 geological clue to the evolution in time of the Subtropical fauna. 

 We do know, however, that it could not have been until after the 

 rise of the Venezuelan Andes and the establishment of a connection 

 therewith sufficient to permit the passage of many alticoline species. 

 This naturally opens up the whole question of the genesis and dis- 

 persion of the fauna of the Subtropical Zone. We find no positive 



