1915 2) 
DISTRIBUTIONAL AREAS 
Close study of the life of any geographic area of large extent invariably 
shows that, in dealing with the ranges of the included species, certain more or 
less definite subdivisions may be usefully recognized. In other words, instead 
of homogeneity in faunal composition, we find marked change from place to 
place; and this change manifests itself in the exclusive presence, in a given por- 
tion of the territory, of certain species, and in the absence of other species, pres- 
ent in contiguous portions of the territory. There is usually conspicuous agree- 
ment in the occurrence of a goodly proportion of the entire complement of spe- 
cies, and this makes possible the characterization of minor areas relatively uni- 
form within themselves. These latter are found to be separated by narrow 
marginal strips of country where species drop out and others come in, and where, 
in the case of subspecies, intergradation of forms takes place. 
Each species or subspecies has a definite range, in which it is normally 
abundant. It is the fact of approximate coincidence in the ranges of several or 
many species that makes it possible to definitely characterize distributional areas. 
These may be of varying rank, according as a greater or less percent of the total 
complement of species is peculiar to each. A good parallel is afforded, in illus- 
tration, by the manner in which characters are used in establishing systematic 
groups; relatively few characters distinguish species and subspecies; progress- 
ively more justify successively higher groups. 
No such proportional treatment as just suggested has as yet been applied 
in the attempt to divide California into zoogeographic areas. Data in hand, 
while seemingly great in quantity, are still not sufficient to afford satisfactory 
basis for statistical analysis. But enough are apparent upon comparatively 
superficial examination to warrant the schemes here employed. These schemes 
are not an innovation; they have grown up gradually, contributed to from 
various sources and by various students, and are therefore believed to express 
somewhere near the facts. 
A major grouping of species geographically is by life zones, in accordance 
with the system advocated by C. Hart Merriam. The ranges of most of the 
land birds given in the present paper are defined primarily in terms of life 
