1917.] Chapman, Distribution of Bird-life in Colombia. 109 



It is not probable that the environment difFers appreciably from the densely 

 forested region lying at the eastern base of the Andes; but that this humid 

 Pacific coastal region is isolated from other regions of essentially similar 

 character is evident. 



To the south, the arid coasts of Peru and northern Chile extend far 

 below the limits of the Tropical Zone. To the east the Andes form an 

 evidently impassable bulwark three zones high, the upper two of which are 

 largely or wholly devoid of forest growth. To the west, lies the Pacific 

 Ocean and, consequently, under existing topographic conditions, these 

 luxuriant coastal forests of northern Ecuador and western Colombia can 

 have received their life only from the north. 



That some of their forms have entered it from this direction is obvious; 

 but they are to be found among the fifty races which represent widely 

 distributed and chiefly Amazonian species. Examples are Cymhilaimus 

 lineatus fasciatus, Myrmoiherula surinamensis pacifica, Tityra semifasciata 

 esmeraldce, Stelgidopteryx r.. uropygialis, Basileuterics fulvicauda, Arremon e. 

 occidentalis, and other birds which have what may be called a completed 

 distribution, that is, occupy all the territory in which they might be expected 

 to occur. 



Once having reached the forested, lower Cauca-Magdalena district, in 

 which they are all represented, there is nothing to prevent these species 

 from ranging southward to western Ecuador through the Colombian coastal 

 forests. 



We cannot, however, regard this Cauca-Magdalena district as the gate- 

 way into the Colombian-Pacific Fauna for those west coast species which 

 are unknown in the Cauca-Magdalena Fauna. Many of these, as has been 

 said, advance westward and northward into Central America and it may be 

 suggested that the autocthonous Colombian-Pacific forms have originated 

 in Central America, since access from other areas seems to be impossible 

 under existing conditions. 



Possibly some of them may have been so derived, but the fact that a 

 large part of them are unknown north of eastern Panama prohibits a belief 

 in their northern origin. Even those species which like Neo-nwrphus sahini 

 and Selinidera spectahilis are found as far north as Nicaragua, assuredly 

 cannot be considered to have entered the Colombian-Pacific Fauna from the 

 north. Both belong to Amazonian groups, and both, in South America, are 

 known west of the Andes only in the humid coast region; neither having 

 been recorded from the lower Cauca-Magdalena district or from western 

 Venezuela. Other species fall into this same class, that is, they are repre- 

 sented in the Colombian-Pacific Fauna and also east of the Andes, but at the 

 north their ranges are apparently not connected. A list of certain species 



