xx LIFE ZONES 



MOUNT SAN JACINTO 



Because of the sharply contrasted desert and Pacific slopes 

 Mount San Jacinto offers exceptional opportunities for the study 

 of Life Zones. (See map.) From the northeast rim there is an 

 abrupt drop of 8000 feet to the Colorado Desert. Here all six 

 Zones from Lower Sonoran to Arctic-Alpine are crowded into the 

 " extraordinarily narrow air-line distance of three miles." "The 

 four upper Zones are almost in superposition. There is probably 

 no other place in North America where the Alpine and Sonoran 

 floras are in such close proximity as they are on San Jacinto 

 Mountain. This is the most southern latitude at which plants of 

 the Arctic- Alpine Zone are known to occur in North America." 

 (Hall.) The mountain is remarkably accessible from the south 

 and the ascent is easily made. A further attraction to the region 

 for students is found in the extensive biological reports on its 

 birds, mammals, reptiles, and flora. 



It is obviously more difficult to assign birds to a particular Life 

 Zone than is the case with plants or even with mammals. Birds 

 which are fairly local during the breeding-season are usually 

 widely scattered when the young are fledged. 



Some birds have a very wide range at all seasons. Thus 

 " White-throated Swifts are found from desert areas to the sum- 

 mit of the San Jacintos. Ash-throated Flycatchers, abundant 

 migrants through the region, breed commonly from the base of 

 the mountains at least as high as 6000 feet." On the other hand, 

 some species occupy such a narrow range that they may be lim- 

 ited to a single plant association: "The Crissal Thrasher of the 

 mesquite belt; Hutton Vireo in the live oak; Gray Vireo in the 

 Greasewood (Adenostema)." 



Investigation of the effect of humidity on distribution of birds 

 of the San Jacinto area shows: 



A. Species occurring regularly on both the Pacific and desert 

 slopes; for example, Arizona Hooded Oriole and Phainopepla. 



B. Species sharply defined in range on either side, such as the 

 Scott Oriole, Crissal Thrasher, and Verdin on the desert slope, and 

 the California Jay, Pallid Wren-tit, and Plain Titmouse on the 

 Pacific slope. 



