BIRDS OF ARGENTINA, PARAGUAY, URUGUAY, AND CHILE 15 

 LIFE ZONES 



After some hesitation on the part of the author there has been 

 inchided in this report a brief sketch of the life zones of the region 

 traversed, a treatment that is necessarily tentative, since it is based 

 on an amount of work in the field wholly inadequate when the great 

 extent of territory included is considered. The limits assigned to 

 the various divisions are thus merely suggestive. Attempt is made 

 only to call attention to major zonal divisions as they appear to an 

 eye trained to such observations in North America. Definite limits 

 and characteristics may be given only with extensive data that may 

 change some of the inferences presented at this place. 



Doctor Dabbene in his Ornitologia Argentina (pp. 169-182) for 

 the whole of Argentina has outlined five major faunas of somewhat 

 different significance than the zones here outlined. Mr. Peters in 

 his recent paper on the summer birds of northern Patagonia (pp. 

 281-283) has found three life zones indicated in the Territory of 

 Rio Negro, which, beginning with the lowest, he numbers Zones 1, 

 2, and 3. 



In the present instance four zones only are considered, the Tropi- 

 cal, Lower, and Upper Austral, and Temperate. Though the term 

 Austral as applied to a life zone was originated jto designate a region 

 in the Northern Hemisphere it may without violence be utilized for 

 the corresponding zone south of the Equator, since in reality it sig- 

 nifies an area adjacent to the Tropics. It is considered preferable 

 to use an established name rather than coin a neAV one. The zone 

 above the two divisions of the Austral is termed the Temperate in 

 accordance with established usage of Goldman, Chapman, Todd, and 

 others in regions near the Equator. 



TUOPICAI. ZONE 



If, as seems logical from experience in other parts of the New 

 World, we adopt the occurrence of frost as marking the southern 

 limit of the Tropical Zone, then the southern Chaco, north to the 

 Rio Pilcomayo in Chaco and Formosa is not tropical, since heavy 

 frosts are of regular occurrence there. In passing up the Rio Para- 

 guay from Asuncion a large-leaved Cecropia^ a tropical tree, was 

 first recorded near the little village of Curuzu-Chica, while the mango 

 tree was first observed a short distance above, at Antioquiera. This 

 appeared to be the limit of dilute Tropical Zone along the Paraguay, 

 though even at this point bananas appeared to have been slightly 

 touched by frost. The winter of 1920, however, had been unusual 

 for severity of cold. Puerto Pinasco and the Chaco behind it ap- 

 peared to be within the lower limit of the Tropical Zone, though 



