1917.] Chapman, Distribution oj Bird-life in Colombia. 23 



As a natural consequence the region is, as a rule, densely forested from 

 the very margin of the sea to the summit of the Western Andes. Buena- 

 ventura lies at the head of the bay of the same name, some fourteen miles 

 from the sea. The shores here are lined with mangroves, and numerous 

 small streams and estuaries make a network of mangrove-bordered water- 

 ways. 



Buenaventura to Caldas. — Shortly after leaving Buenaventura, on the 

 railway to Caldas, one reaches higher ground and enters the true coastal 

 forest. The trees are not of great height but the growth is luxuriant in the 

 extreme, the floor of the forest as well as limbs of trees being covered with 

 vegetation, making progress off trails or clearings impossible without the 

 aid of a machete. Richardson, who collected in this coastal forest at San 

 Jose and Cisneros, considered it the most difficult ground to work he had 

 encountered in a field experience of twenty-five years in the tropics. The 

 density of the vegetation limits one's radius of action and makes it difficult 

 to shoot birds as weU as to find them when shot; the high degree of humid- 

 ity prevents them from drying properly, while the abundance of mosquitoes, 

 as well as of other insect pests, makes the region extremely trying and 

 unhealthful. Both Richardson and his native assistant suffered severely 

 from fevers acquired in this low coast region, the avifauna of which is still 

 far from exhausted. 



The Caldas Basin. — -A short distance east of Cisneros, and some 1500 

 feet above it, the railroad, still following the shores of the Dagua, passes 

 through a narrow canon worn by the river, and emerges in a surprisingly arid 

 basin or pocket in which lies the settlement of Caldas (alt. 2560 feet). The 

 floor of the valley, and at least lower slopes of the hUls by which it is sur- 

 rounded, are covered with short grasses with occasional stands of low cac- 

 tus, acacia-like trees and agaves. The abrupt change in climate, indicated 

 by the striking difference in the vegetation of Cisneros and Caldas, is evi- 

 dently due to the presence of a ridge at the western border of the Caldas 

 Valley of sufficient height to protect the area lying east of it from the pre- 

 vailing western winds and, consequently, from receiving a share of the 

 moisture they carry. A part of this moisture is given up as the air-currents 

 strike the Pacific slope of the ridge which borders the Caldas basin on the 

 west, with the resulting heavy rainfall of the western slope. In passing over 

 or pouring down into the valley at Caldas, the temperature of the air is 

 doubtless raised rather than lowered and its moisture-carrying capacity 

 correspondingly increased. Consequently, further condensation does not 

 occur imtil the higher mountains to the east are reached, and with the 

 increase in rainfall the forests reappear. 



This treeless depression or valley on the Pacific slope of the Western 



