1^13] Grinnell-Swarth : Birds and Mammals of San Jacinto 383 



BOREAL FAUNA OF SAX JACINTO PEAK COMPARED 



WITH THAT OF OTHER MOUNTAINS OF 



SOUTHERN CALIFORNIA 



Although the Boreal zone of the San Jacinto area is sharply 

 cut off on all sides, and is thus completely isolated at the present 

 time from other areas of similar fauna, there is good reason to 

 suppose that during a more or less remote period, of cooler cli- 

 mate, there was zonal continuity with the adjacent ranges and 

 these in turn with the vast Boreal area believed to have once 

 prevailed over the Great Basin region and to have included the 

 Sierra Nevada. Changes in topography so modified meteorologi- 

 cal conditions that the zones of life of necessity retreated north- 

 wards and upwards until restricted to the higher elevations now 

 distantly separated from one another. 



The mammals and birds of the high mountains of southern 

 California in every case are either identical with, or show close 

 relationship to. forms now existing in the Sierra Nevada. 



In reviewing the Boreal biota as found to occur on San 

 Jacinto Peak, the first thing to attract particular attention was 

 the relative paucity of types as compared with the number of 

 types in the San Bernardino Mountains previously studied (Grin- 

 nell. 1908). As shown in the accompanying table there are seven 

 distinctly Boreal mammals and twenty-eight Boreal birds on the 

 San Bernardinos, while there are but five mammals and twenty- 

 two birds of like zonal restriction on the San Jacintos. Only 

 one (Mush la arizonensis) , out of the whole number belonging 

 to the San Jacintos. lias not been found on the San Bernardinos, 

 and the probabilities point towards its existence there also. 

 Otherwise all of the San Jacinto species are found on the other 

 mountain mass. These relative conditions are closely paralleled 

 in a study of the plants of the two areas (see Hall. 1902, pp. 47. 



48). 



This disparity in Boreal representation appeared to be with- 

 out explanation, until it occurred to us that there might be some 

 correlation between size of the areas concerned and numbers of 



