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



castaneiceps (found in the forests on the west slopes below Andalucia), 

 Myiotriccus o. phcenicurus, Tanagra chilensis, and Schistochlamys air a. 



It should be added that our work has been done about the borders of 

 this upper Magdalena district. Of the fauna of the floor of the valley, I 

 feel that we have still much to learn. 



The second southward extending arm of the Cauca-Magdalena Fauna 

 enters the Cauca Valley from Antioquia and reaches almost to Popayan. 

 It seems highly inaccurate to speak of so fertile a district as the Cauca 

 Valley as arid, nevertheless, in the light of our present knowledge, it must 

 be ranked as an arid branch of the Cauca-Magdalena Fauna. 



The marshes and bayous of the Cauca River support a variety of aquatic 

 and palustrine species unknown to the dryer upper Magdalena, but aside 

 from this difference there is a marked similarity in the Tropical Zone life 

 of each. 



There is more forest growth in the Cauca than in the upper Magdalena 

 Valley, in spite of widespread deforestation. Localities like those visited 

 by Allen and Miller at Rio Frio, and the country through which we passed 

 about Guengiie, seem well-adapted to the needs of forest-haunting species; 

 nevertheless, we have thus far failed to find in the Cauca Valley a single 

 representative of the families Momotidae, Trogonidce, Galbulidw or Biic- 

 conidce, and but one species of Ramphastidce, the widely distributed Aulaco- 

 rhynchus hcBmatopygms. 



Possibly the comparatively limited amount of forest-growth may account 

 for the apparent absence of those species of these groups which inhabit the 

 lower Cauca region, and might therefore be expected to occur in the Cauca 

 Valley. But it is evident that its isolation, and the fact that the Tropical 

 Zone enters it at the north where it is separated from the forests of the lower 

 Cauca by long stretches of treeless, truly arid country, are all factors which 

 must be taken into consideration in accounting for its apparently limited 

 life. That this life is actually limited I believe to be a fact, but I also 

 believe that further collecting in the forests of the valley will result in the 

 discovery of species which have not thus far been taken there. 



In spite, therefore, of the physical differences between the upper Mag- 

 dalena and Cauca Valleys, their land-bird life is much the same. In both 

 instances it has been derived indirectly from east of the Andes by a current 

 which appears to. have flowed northward around the end of the Eastern 

 Andes, and thence southward up to the heads of the valleys. 



The upper Magdalena, being far more accessible geographically, and 

 having a narrower belt of humid tropical forest at its mouth, has received 

 the greatest number of species. The following common birds for example, 

 of the upper Magdalena are as yet unknown from the Cauca Valley: Broto- 



