Zoogeographical notes on the «nonforest» lowland bird faunas of northwestern South America

Abstract

The fauna of the unforested lowlands of Venezuela and Colombia is closely related to that of the non-forest regions of Brazil and eastern Bolivia. Endemic genera are very few, and the number of endemic species is comparatively small. The dry intermontane valleys of the Colombian Andes were populated from the Caribbean lowlands to the north. Endemic forms of these valleys have reached the subspecies level, and some are markedly different. The faunal exchange between the Colombian and Central American open-country fauna was rendered difficult even during the dry climatic periods of the Pleistocene, due to partial flooding of the northern Colombian plains. The fauna of the arid Pacific coast of Ecuador and Peru has a great number of endemic genera and species. Some relations to the Brazilian non-forest fauna via the upper Marañón valley and dry pockets along the eastern base of the Peruvian Andes are evident in this fauna. It is concluded that part of the Brazilian non-forest fauna surrounded the Amazonian forest in the east (along the Atlantic coast) and in the west (along the base of the Peruvian Andes to reach the upper Marañón valley) during dry climatic periods of the past, when the distribution of the forests was more restricted. A connection between the Colombian–Venezuelan non-forest fauna and the arid Pacific fauna of Ecuador and Peru was prohibited by the Chocó forests (and the Chocó Refuge) along the Pacific coast of western Colombia. These forests formed a barrier to the non-forest fauna ever since they developed during the early Pleistocene uplift of the Colombian Andes.