86 University of California Publications in Geology [V 0L - 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 nights 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 

 group, though no more maritime and no more capable a flier 

 than the cathartic! vultures. It might be suggested as a dis- 

 tinction between these two eases 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 



20 Coues, E., Key to N. Am. Birds (ed. 5; 1903), vol. 2. 



