Raptor es of South America. 
353 
destructor, Sw.) which perhaps more than any other species may 
be considered a forest bird, always follows the banks of rivers. 
By dividing all these birds into three classes, and considering the 
number of species which inhabit, Jirst, the wooded lands which we 
have just described; secondly, the arid plains merely covered with 
small bushes ; and finally, the mountains ; the amount of species in 
the wooded plains will be thirty-three, that is, more than three- 
fourths of the whole species observed ; in the arid plains it will be 
nineteen, that is, less than the half of that number, and sixteen, or 
rather more than a third, for the mountains. It will be understood 
that these numbers include the species which continually pass from 
one locality to another. 
From all these observations it follows that the number of species 
decrease proportionally as we advance from the warm regions to the 
pole, or as we ascend from the low-lying lands of the tropics to the 
summit of the Andes : and nearly for the same reason, they like- 
wise diminish in their passage from wooded tracks to plains, and 
from plains to mountains. The following little table affords, in a 
condensed form, a comparative scale of this system of decrease in 
the number of species. 
ZONES. 
G 
O ^ 
. <K 
C 
fc 
OF LATITUDE. 
( Scale ofdegrees) 
0.8 
6 % 
* & 
OF ELEVATION. 
Above the level of the sea 
(to 15 of latitude.) 
<~ 02 
.s 
6 8 
* & 
OF HABITATION. 
According to the na- 
ture of the country. 
j 
2J yj 
1st, 
From 11 to 28 
28 
From to 5,000 feet. 
28 
Woody places, marsh- 
es, natural waters. 
33 
2d, 
From 28 to 34 
19 
From 5,000 to 11, 000 f. 
9 
Arid& shrubby plains 
19 
3d, 
From 34 to 45 
17 
Upwards of 11, 000 feet. 
9 
Elevated mountains 
16 
It may be asked why the greatest number of rapacious birds in- 
habit warm regions, and particularly places in which marshes occur 
and detached tufts of wood. The reason is, that the majority of 
South American birds of prey do not feed solely on small birds and 
quadrupeds, like the greater part of European species, but likewise 
on land and aquatic reptiles which abound in such situations, as 
well as on fishes and even insects. In America the falcons are the 
only Raptores which habitually pursue birds and mammiferee ; all 
the others eat animals of every description ; a circumstance which 
made Azara * suppose that the American birds of prey might share 
the characteristic indolence of the inhabitants of this quarter of the 
world. They are in reality much less active than those of Europe, 
with the exception of the Falconidae, which every where exhibit 
* Voyages dans I'Amerique Meridionale, Tom. iii. p. 5. 
