2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I50 



through the order that includes the shorebirds, gulls, and their 

 allies. A general account of personal field work, with a review of 

 the studies of other ornithologists, and general discussions of the 

 avifauna will be left for the end. 



It may be sufficient here to outline briefly the character of the 

 isthmus as included in the present political boundaries of the Republic 

 of Panama. The entire Caribbean slope and eastern Darien on the 

 Pacific side are the regions of heaviest rainfall. In the northwest, 

 in the Province of Bocas del Toro, there is no marked break in 

 precipitation for any lengthy period throughout the year. The 

 Pacific slope, from the Costa Rican boundary eastward, has a definite 

 dry season, mainly between the latter part of December and the 

 middle or end of April. Because of this difference the denser forest 

 areas are found on the north and in Darien, where originally tree 

 growth was continuous. On the Pacific side there are extensive 

 areas of open savannas. And forest where found is more open and 

 in part deciduous, so that many trees lose their leaves in dry season. 

 These were the original conditions, now extensively modified over 

 great areas that have been cleared for agricultural use. These 

 changes are most marked from the western boundary in Chiriqui 

 east through the Province of Panama, where most of the original 

 forest cover is gone, and are proceeding rapidly elsewhere. The 

 main areas that still are primitive lie on the Caribbean drainage in 

 the inland mountain and hill area of interior Bocas del Toro, over 

 the interior hills of San Bias, and on the Pacific side on the 

 mountains and hills of the interior from the eastern end of the 

 Province of Panama through Darien. 



The isthmus in the main is in the Tropical Zone, with subtropical 

 zone forest in the mountain regions of the western half. Additional 

 areas of the latter zone of lesser extent are found along the central 

 spine of the Azuero Peninsula, and in the mountains near the 

 Colombian boundary. Limited Temperate Zone conditions extend 

 across the top of the Chiriqui volcano and on some of the higher 

 ridges to the east in Chiriqui and Veraguas. 



THE LIST OF BIRDS 



Each family is introduced by a brief general statement on the 

 group as a whole throughout its entire range. This is followed, where 

 necessary, by a key to the species that have been recorded in 

 Panama, based on the most evident characters of color, size, and 

 form. While this may be of assistance in naming birds in Hfe, it is 



