86 University of California Publications in Geology [Vou-7 
of palaeontological study is the raptorial subdivision embracing 
the New World vultures. The exclusive possession by the 
Americas of so marked a group of large and strong-flying birds 
as the Cathartidae and the total absence there of any form of 
the true Vulturidae, which occupy the same bionomic position 
in the Old World, is one of the striking phenomena in animal 
distribution. Aside from the fact that the group is so well 
defined, there being no Recent forms showing transition between 
it and the other raptorine subdivisions, we find it not poor in 
species and it is widely distributed in the western hemisphere. 
There are endemic to the New World no less than five distinct 
cathartine genera—a goodly number for a group, the smallest 
member of which approaches in size the largest eagles. All are 
birds capable of long-sustained flights and they are unsurpassed 
in their ability to meet the emergencies of changed elevation 
and shifting air currents that would prove disturbing to less 
perfect fliers. This very factor may, by insuring them against 
being driven astray by storms, bring about a distribution more 
in accord with their own needs or inclinations. 
As an instructive comparison in the matter of distribution 
one might consider the short-eared owl (Asio flammeus). This 
bird is almost cosmopolitan, occurring unmodified over both 
hemispheres and even in such isolated islands as the Hawaiian 
eroup, though no more maritime and no more capable a flier 
than the cathartid vultures. It might be suggested as a dis- 
tinction between these two cases that the vultures are non- 
migratory and are confined to the tropics, and would, therefore, 
have no tendency to wander, would not be exposed to the danger 
of scattering by storms and would always be separated from the 
other continents by the widest parts of the ocean basins. An 
examination of the ranges and the habits of the existing species 
will, however, prove the fallacy of such views. Cathartes aura 
is migratory or not as occasion demands. It is resident to 40° N 
latitude and thence northward it becomes migratory, being 
starved out in winter. Its habitual range extends from 55° N 
latitude to Tierra del Fuego and the Falkland Islands on the 
south.*° 
20 Coues, E., Key to N. Am. Birds (ed. 5; 1908), vol. 2. 
