Bulletin - United States National Museum - si-pddr - Smithsonian ...

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 Tropical,
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 Paraguay
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 appeared
to be within the lower limit of the Tropical Zone, though