102 Annals of the Carnegie Museum. 



all the life-zones and permitting latitudinal extension of range to have 

 taken place at a lower level than would be possible under present 

 climatic conditions. 



Summary and Conclusion. 



The bird-life of the Santa Marta region, considered from the dis- 

 tributional standpoint, falls naturally into four primary divisions or 

 zones, which are coordinate with those represented in the Andean re- 

 gion of Colombia. These life-zones are the Tropical, Subtropical, 

 Temperate, and Paramo. The Tropical Zone alone has terminal coni- 

 nections on either hand, being continuous with this zone as represented 

 in adjacent parts, while all the zones above the Tropical are here 

 strictly altitudinal, and entirely isolated from the corresponding zones 

 elsewhere. They may be considered as faunal islands, and show in 

 their depauperate fauna one of the recognized characteristics of 

 islands. The diminution in the number of forms observed in ascend- 

 ing the mountain slopes appears to be greater and more abrupt in the 

 Santa Marta region than in the Colombian Andes, which circumstaiice 

 tends to add to the general impression that we are dealing with a fauna 

 of insular character. Each life-zone may be regarded as a composite 

 of the various elements, or species, which go to make it up, or as an 

 association or assemblage of forms having approximately the same 

 general , range. The limits of any given zone, therefore, are as 

 sharply or as loosely defined as the range of the various species which 

 characterize 'it. We find that on the north slope of the Sierra Nevada 

 de Santa Marta, owing to local conditions which involve the govern- 

 ing factors of temperature and humidity, there is a tendency toward a 

 general lowering of the life-zones, causing a certain amount of over- 

 lapping in the ranges of some species which otherwise would not be 

 found together. 



The Tropical Zone comprises by far the larger part of the area of 

 the region as a whole and comprehends more than three-fourths of its 

 bird-life. Its fauna is exceedingly diverse in character, including as 

 it does representatives of families and groups having widely different 

 habits and haunts. It may be divided roughly into two belts, based 

 on altitude, a Littoral or Lower Tropical and a Piedmont or Upper 

 Tropical. Of these the Littoral possesses the larger number of 

 species, while the Piedmont has few species peculiar to itself, being 



