THE NEOTROPICAL REGION 



The notably distinct Neotropical Region embraces all of South and Central Amer- 

 ica, the West Indies, and the southern part of Mexico as far north as the limit of 

 the tropical forest. The diversity of its bird fauna is unequaled by that of any other 

 zoogeographical region, and no other exhibits so marked a degree of endemism. Only 

 the Australian Region is older in point of continuous isolation and, as might be ex- 

 pected, the endemic fauna of each includes a preponderance of generalized, or "more 

 primitive" types of birds whose ancestral forms evolved long before the less ancient 

 Regions became completely isolated. 



Two orders of birds, the Rheiformes (rheas) and Tinamiformes (tinamous), as 

 well as some twenty-seven families, are entirely restricted to the Neotropical Region. 

 Several additional families, notably hummingbirds, cotingas, flycatchers, troupials 

 and tanagers, are essentially Neotropical in origin and distribution, although represen- 

 tatives of each now occur in North America as well. It is not to be supposed, of course, 

 that each of these endemic groups is represented throughout the Region. On the con- 

 trary, the present-day distribution of birds at family level varies considerably, just as 

 does the distribution of genera and species within a single family. 



Many endemic Neotropical families are notably widespread, but some, like the 

 palm-chats and todies of the West Indies, the oil-birds of Trinidad and northern South 

 America, and the seed-snipe and cariamas, to mention a few, occupy relatively limited 

 ranges. Others, like the sharp-bills (Oxyruncidae), have a discontinuous range, an 

 explanation of which must be sought in the past. The diverse patterns of distribution 

 found within a single zoogeographical region stem largely from the variables of isola- 

 tion within the region. Isolation of one kind or another is a prerequisite of differentia- 

 tion among birds. There may be isolation in time as well as in space, or a combination 

 of the two. Thus the time and place of origin, even more than present ecological condi- 

 tions, determine the distributional pattern of many birds. 



The Neotropical Region is notably diverse in habitat conditions. It extends over 

 many degrees of latitude, embracing both lowlands and mountain ranges, and deserts 

 as well as humid jungles. Within it may be recognized several Subregions, each more 

 or less clearly defined and characterized by endemic species, genera, or even families 

 of birds. The most distinctive Subregion is the Antillean, which includes most of the 

 islands of the ^Vest Indies. Many birds of Nearctic origin are found in this Subregion, 

 but its fauna is nevertheless much more closely related to that of Central and South 

 America, as shown by the preponderance of families common to both. Two families of 

 birds, the palm-chats and the todies, as well as numerous genera and species, occur 

 only in the West Indies. Other less clearly defined Subregions are the Central Ameri- 

 can, Amazonian, Brazilian, and Patagonian. 



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