76 Annals of the Carnegie Museum. 



can be fairly sure, therefore, that there is at least a narrow strip of 

 Humid Tropical Zone forest extending around the northern end of the 

 Eastern Andes, as suspected by Dr. Chapman, which would probably 

 suffice to carry the forms of this zone in from the east. We have no 

 certain knowledge of the birds of this narrow strip, however, beyond 

 a list of seventeen species given for Manaure by Simons, some of which 

 may have come from the forest zone.^" 



Of the twenty- four species given by Dr. Chapman as characterizing 

 the Humid Cauca-Magdalena Fauna (i.e., not found elsewhere) no 

 less than nine have penetrated to the Santa Marta region. (These 

 are in addition to the forms already specified as having entered this 

 Fauna from either side.) (See Figure 3.) As recently ascertained 

 by the junior author, there is every indication of a direct connection 

 existing between the humid forest areas of the Santa Marta region- 

 on the one hand and those of the middle Magdalena and the western 

 slope of the Eastern Andes on the other, which would of course readily 

 account for the intrusion of so many characteristic and semi-charac- 

 teristic Humid Cauca-Magdalena forms in the Santa Marta region. 

 Such a connection would of course destroy the continuity of the Arid 

 Tropical, and would oblige us to suppose either that certain forms of 

 that zone had in fact been able to cross the intervening unsuitable 

 humid belt to establish themselves in the available areas beyond, or 

 else that their dispersion was effected prior to the change in condi- 

 tions which permitted the Humid Tropical forms to enter. We are 

 inclined to favor the latter view, while at the same time admitting that 

 unsuitable habitat may not necessarily be an absolute barrier against 

 the dispersal of species in the Tropical Zone. This is probably par- 

 ticularly true in the case of birds, which are able to traverse great 

 distances with such comparative ease. The evidence derived from a 

 study of the present distribution of the forms of the Tropical Zone in 

 the Santa Marta region goes to show that the Arid Tropical Venezuelan 



16 The species represented are as follows : Ictinia plumbea, Falco sparverius 

 isahellinus, Pteroglossus torguatus nuchalis, Ramphastos ambiguus abbreviatus , 

 Ramphastos piscivorus brevicarinatus, Chlorostilbon russatus, Chalybura buf- 

 fonii aneicauda, Sittaso-mus sylvioides levisf, Dendroclncla lafresnayei lafres- 

 nayeij Chiroxiphia lanceolata, Muscivora tyrannus,^ Myiodynastes THaculatus 

 maculatus, Onychorhynchus mexicanus fraterculus, Tersina viridis occidentalis, 

 Basileuterus delattrii mesochrysus, Cyanerpes cyaneus, and Cassidix oryzi- 

 vora violea. 



