10 PACIFIC COAST AVIFAUNA No. 11 
zones, and the extent of these distributional units, as represented within the 
boundaries of California, is shown roughly on the map, plate I. The cross-see- 
tional profiles given on plate II serve to convey some interesting suggestions as 
to the effect of altitude and distance from the sea upon the ranges of the various 
animals severally concerned. 
Of lesser rank are faunal and subfaunal areas, using the term ‘‘faunal’’ in 
a restricted or special sense. These areas, as the writer conceives of them, are 
naturally subdivisions of life zones, so that each faunal unit consists of a divi- 
sion of one life zone. The system of nomenclature for faunal units ought logically 
to indicate their relationships accordingly ; but it does not. As a matter of prae- 
tical necessity in most cases, divisions of two or even more adjacent zones are 
lumped together under one faunal name (compare plates I and IIT). 
It is natural to try to find some underlying causative factor to account for 
the two types of distributional behavior involved in the two schemes, of life 
zones and faunal areas. Study of the maps, of conditions in the field, and of 
statements of distribution concerning our birds and other vertebrate animals 
has forcibly suggested that adjacent zones are demarked from one another by 
increase or decrease of temperature beyond in each case certain critical points. 
Thus, in ascending a mountain, such as San Jacinto Peak, while there is little 
doubt but that there is a uniform gradient in temperature from warm to cold, 
one is impressed with the fact of zonation,—the existence of belts of life suc- 
cessively passed through, broadly uniform, with narrow intervening bands of 
blending. 
The great topographic diversity in California, together with the presence 
of the sea with the cool air-currents moving in a prevailingly eastward direction 
from it, are factors which may be readily cited as accounting for the intricate 
pattern of the life zones as shown on the map of this state. It is not necessary to 
specify precise temperatures, in degrees, as delimiting zones (and this has not 
yet been attempted critically by any one for California), in order to comprehend 
what the writer believes to be trne—that temperature is the most important sin- 
ele one of the several factors controlling the ranges of our birds. How this con- 
trol is exerted upon each species concerned is a problem as yet incompletely 
solved, but it seemingly has in many eases to do with the period and processes 
of reproduction. 
Broadly speaking, we may recognize two main zonal contingents in the ver- 
tebrate life of California, Boreal, or northern, and Austral, or southern. Because 
of the dominance here, in effect upon temperature, of altitude over latitude, we 
might explain the situation more clearly to the inexperinced by speaking of the 
animal life of the cool mountains as compared with the animal life of the warm 
valleys. The contrasted differences are enormous, as even a cursory survey will ; 
suffice to show. No close observer will deny that the critical factor here is that 
of temperature. 
By considering the whole of North America we are able to readily justify 
zonal subdivision a step, and only one step, farther, as indicated in the following 
brief synopsis of life zones. 
