1908] Grinnell—Biota of the San Bernardino Mountains. 25 
very rough estimates of their numbers in the region under con- 
sideration: golden eagle, 8; Williamson sapsucker, 180; Pacific 
nighthawk, 360; calliope hummingbird, 360; gray flycatcher, 
3760; Clarke nuteracker, 250; Cassin purple finch, 6000; Sierra 
juneo, 10,000; Stephens “fox sparrow, 680; Cassin vireo, 4480; 
Audubon warbler, 10,000; American dipper, 24; Sierra creeper, 
840: mountain chickadee, 8000; ashy kinglet, 50; Townsend soli- 
taire, 360; Sierra hermit thrush, 360; western robin, 650: western 
bluebird, 4000. 
Some birds, such as nuthatches and chickadees, raise broods 
of six young; others, like gray flyeatchers, warblers, fox sparrows, 
and juneos, raise four young; still others, such as wood pewees, 
only three; and others like hummingbirds and nighthawks, only 
two. Takine all this into consideration, and also the accidents 
and fatalities on the one hand, and the probability of there being 
two broods in a season with juncos and some other species on the 
other, I believe a very conservative estimate would place the full- 
erown young-of-the-year appearing up to the end of the breeding 
season, at an equal number to the adults. In other words. the 
population will have at least doubled by the middle of July, 
when there will therefore be nearly one million birds in the re- 
gion. Now, if we take into consideration the vast hordes of July 
invaders from elsewhere, spoken of above, I should consider the 
population -to have then consisted at the very minimum of two 
million individual birds. And yet there appeared to be a boun- 
tiful food supply at all times during the summer, enough to 
support easily a still larger population. Now what becomes of 
this population ? 
It is almost needless to recall that the aggregate population 
probably remains constant from year to year. For some species 
may be increasing, some decreasing, while others remain in a 
stationary status; and then, of course, the entire population may 
dwindle below the average during unfavorable years (dry years 
or when forest fires ravage the region), or it may swell during 
series of propitious years. But we ean take the average from 
all this as a maintained constant population. In the area under 
consideration, take the above estimate as 491,520 breeding birds 
at the time of least population, or in round numbers half a mil- 
