16 



BULLETIN 133, UNITED STATES NATIONAL MUSEUM 



even here it did not seem to me that the typical tropics had been 

 reached. From this point the line limiting the Tropical Zone may 

 swing down in the west into the lowlands of Salta and Jujuy, and 

 in the east to include part of the Territory of Misiones. As the land 

 through the interior is comparatively level, transition between Tropi- 

 cal and the succeeding zone is very gradual. The folloAving forms of 

 birds taken at Puerto Pinasco were not secured farther south. Some 

 of them, however, are recorded for eastern Salta, Jujuy, or for 

 Misiones : 



Heterospisias merldionalis meridion- 



alis. 

 Pyrrhura frontalis chiripepe. 

 Trogonurus variegatus hehni. 

 Dendrocolaptes picumnus. 

 Lepidocolaptes angustirostris cer- 



thiolus. 



SyrMllaxis albilora. 

 Troglodytes musculus niusculus. 

 Turdus albicollis. 

 Basileutcrus hypoleucus. 

 Basileuterus flaveolus. 

 Myospiza humeralis humeralis. 



LOWER AUSTRAL Z0NE3 



A moderate climate, one where frost may occur regularly but snow 

 only casually, characterizes the greater part of the level sections of 

 eastern and northern Argentina, extending south to the valley of the 

 Rio Negro and on the north including Uruguay and a portion of 

 southern Paraguay. As the zone that succeeds the Tropical belt it 

 may be called the Lower Austral Zone. Though varied in its char- 

 acteristics, it is readily divisible into at least two sections — one arid 

 and the other humid. The level eastern pampas lie within the humid 

 section of this zone, which includes also the Argentine Chaco. To- 

 ward the interior there is a gradual decrease in amount of annual 

 rainfall, with a corresponding transition to a condition of aridity 

 characterized by broad, dry plains grown with scattered scrub of 

 calden (Prosopis nigra), piquillin {Gondalia lineata), or perhaps 

 broad areas covered with creosote bush {Covillea divaricafa), atri- 

 plex {Atriplex Imnpa and A. crenatlfolia), and others. This zone 

 'covers the broad flats of eastern Mendoza to the base of the moun- 

 tains, where it penetrates among the winding valleys into the foot- 

 hills to about 1,200 meters altitude (in that latitude) and extends in 

 the interior from Santiago del Estero and La Rioja south to the 

 valleys of the Rio Colorado and Rio Negro in northern Patagonia. 

 It corresponds to Peters' Zone 1 in Patagonia, which, according to 

 him, prevails in the Territory of Rio Negro below " 1,000 to 1,500 

 feet," and extends up the valley of the Rio Limay to a point between 

 Paso Limay and Senillosa. It is also the zone of central Chile. 



The Lower Austral Zone is characterized by the following breed- 

 ing; birds: 



