USE OF THE MAP 
Tue four Life Zones indicated on the accompanying 
map are those mentioned in the data given under the 
headings Geographical Distribution and Breeding Range. 
They represent climatic conditions of temperature in the 
regions indicated. The ‘‘ Boreal”’ extends from the tree- 
less, snowclad summits, far above the timber-line down 
through the coniferous forests. Next in coldness is the 
b 
‘¢ Transition,’ which begins at the Yellowpines, overlap- 
ping the Boreal a little, and containing some species of 
oaks, buckbrush, manzanita, and some sagebrush. Lying 
between the Transition and the almost tropical heat of 
the ‘‘ Lower Sonoran” is the ‘* Upper Sonoran,” where 
we find the juniper, oaks, piNon pines, and sagebrush. 
Last of all, the **‘ Lower Sonoran’ 
’ 
is the warmest. In it 
lie the hot valleys and desert regions of California, and 
here flourish the live oaks and mesquites. Many Cali- 
fornia birds migrate from one to another of these zones 
during the breeding season, as the birds of the Eastern 
United States migrate north and south. This changing 
from lower to higher altitude, or the reverse, is termed 
vertical migration. 
