BIRDS OF SOUTHERN VERACRUZ — WETMORE 223 



Across the higher sections of Cerro de Tuxtla and Volcan San 

 Martin there is a small area that belongs with the Subtropical Zone, 

 though these elevated portions are too small in total extent to sup- 

 port an extensive avifauna characteristic of this higher zone. The 

 Subtropical element here must be considered a remnant or fragment 

 from the cooler climatic conditions of the Pleistocene, preserved at 

 its present rather low elevation through the fact of the extensive cloud 

 banks with accompanying rains that cover the mountain peaks for 

 much of the time with the modification of temperature that they 

 bring. The northern location of the mountain mass between latitudes 

 18° and 19° N. must also be considered a contributing factor in this 

 preservation, as also must its isolation by lowlands and the conse- 

 quent full exposure of the higher slopes to cold winds. The list of 

 birds that may be considered as of Subtropical affinity is as follows : 



Oreopeleia lawrencii carrikeri 

 Campylopterus hemileucurus hemileucurus 

 Pampa pampa excellens 

 Aulocorhynchus prasinus prasinus 

 Lepidocolaptes aflinis afflnis 

 Xenicopsoides montanus variegaticeps 

 Empidonax flavescens imperturbatus 

 Turdus assimilis leucauchen 

 Myadestes unicolor unicolor 

 Catharus mexicanus mexicanus 

 Hyioborus miniatus molochinus 

 Basilcuterus culicivorus culicivorus 

 Basileuterns belli scitulus 

 Piranga leucoptcra leucoptera 

 Chlorospingus ophthalmicus ophthalmicus 

 Atlapetes apertus 



From a survey of the complete list of these mountain birds, the im- 

 pression comes to me that the Subtropical elements, here near the 

 northern limit of their latitudinal range, tend to descend lower than 

 in the mountains of Central America, either regularly or casually, so 

 that the demarcation of the Subtropical area from the Tropical Zone 

 is less distinct than usual. This is reasonable when we consider that 

 we are here in the northern sector of the Tropical area and that those 

 elements of a subtropical nature that are found are undoubtedly af- 

 fected by the prolonged period of heavy rains, which bring lowered 

 temperatures, and by the constant sweep of cold storms from the north 

 from November to the end of March, the "northers" of the Texas 

 plains, in Mexico called nortes. Some species of the higher-zone ele- 

 ment in the Sierra de Tuxtla range down to between 2,000 and 3,000 

 feet elevation, though in Central America to the south the same types 

 of birds occur only at much higher levels. In the section on migration 

 in the present paper, it is remarked that stragglers of such high- 



