﻿VENEZUELAN ORNITHOLOGY — FRIEDMANN AND SMITH 413 



ponds. Toward the end of the wet season the mesa is covered with 

 many temporary ponds, some of considerable size. Often these are 

 semipermanent bodies of water, disappearing completely only during 

 the driest years. 



In this area conditions are not favorable for the formation of top- 

 soil. Since the surface soil is in effect the essentially unaltered geo- 

 logical outcrop, the vegetation it supports is remarkably distinctive. 

 A map of the exposed strata gives an excellent idea of the extent of 

 the major habitats and of the local distribution of the birds character- 

 istic of these habitats, since the surface soil is relatively unmodified by 

 humus and since the area studied does not vary greatly either in 

 respect to altitude or local weather conditions. Within the area the 

 two outcrops are: (1) Mesa (Quaternary-Pleistocene) composed of 

 pebble, cobble, and boulder gravels, originating mainly from coalescing 

 alluvial fans due to the rapid eroding of Cretaceous and Tertiary rocks 

 of the mountains. The surface of this formation tends to remain 

 intact owing to the presence of resistant iron-oxide-cemented capping 

 layers. (2) Sacacual-Las Piedras (Pliocene), a series of nonmarine 

 claystones, siltstones, sandstones, and some pebbly beds. 



The sketch map (fig. 46) shows the approximate extent of the 

 Sacacual-Las Piedras outcrops and of that portion of the mesa forma- 

 tion outcrop forming the Eastern Venezuelan Mesa (200-meter con- 

 tour line). Actually, the mesa formation outcrop continues eastward 

 to the coast, but the progressively lower altitude and the increase of 

 recent alluvium deposits presumably change the nature of the vegeta- 

 tion enough to effect changes in the avifauna of that region. The limits 

 of the savanna climax, as described in this report, correspond to those 

 of the Eastern Venezuela Mesa. 



While not shown on the sketch map, it should be remembered that 

 the Sacacual-Las Piedras formation, with the consequent deciduous 

 seasonal woods, is exposed wherever the rivers have cut through the 

 mesa cap. The soil of this mesa, low in phosphorus and nitrogen 

 content, will hardly support a more profuse vegetation, even in the 

 vicinity of water, unless it be the addition of the moriche palm 

 (Mauritia flexuosa) . 



The extent of the deciduous seasonal woods climax of the Sacacual- 

 Las Piedras formation is somewhat less certain, but from personal ob- 

 servation and careful questioning the junior author believes it con- 

 tinues throughout the extent of the outcrop. 



It is apparent, therefore, that the area occupies a central position in 

 respect to habitats studied and that the influence of other life zones 

 on the distribution of the avifauna is minimized. The great excep- 

 tions to this are the Amana and Guarapiche Rivers flood plains in the 

 northeast corner of the area. Although these two rivers cut through 

 the mesa to the Sacacual-Las Piedras formation to more or less the 



