a OTs 
Pt BIOLOGICAL FOURNAL. 
Vou. I. ‘NOVEMBER, 1890. No. 9. 
: THE GEOGRAPHICAL DISTRIBUTION OF LAND ) BIRDS 
3 IN CALIFORNIA. 
[With Plate IX.] 
II. THE BOREAL PROVINCE. 
BY CHARLES A. KEELER. 
In considering in detail the avifaunal regions of California, the 
areas of the Boreal Province will first claim our attention. The 
Boreal Province of pre-glacial times was doubtless confined to a 
region far north of California, whence it was pushed southward by 
the ice, encroaching, probably, on the more tropical forms of life 
which then inhabited the country. When the cold abated the more 
plastic northern forms became acclimated to a warmer region, and 
now form a part of the Sonoran Province, while the more stable 
_ genera or species followed the receding ice northward or to a higher 
altitude in the same latitude. Accordingly we find in California 
that the Boreal forms have become stranded on our two mountain 
ranges. Although the Boreal Province may be naturally. divided 
into two areas, one occupying each of the mountain chains, it bears 
the unmistakable stamp of unity, which indicates that the two areas 
have been differentiated in recent geological time; apparently in 
e post-glacial period. We find many characteristic Boreal species 
common to both areas, as, for example, the California pygmy OW? 
Jarris’s | woodpecker, olive-sided flycatcher, Cassin’s vireo and 
ern creeper. Then there are a number of forms found in both — 
in which there is merely a varietal difference. Among these 
1ay be mentioned the two varieties of the mountain partridge—one 
cu in in the Coast Range and the other in the Sierra Nevada 
ntain ‘There are, nevertheless, quite a number of species 
