22 University of California Publications in Zoology. (Vou. 5 
mountain slopes, were noted at this watering place. Among mam- 
mals we noted the desert jackrabbit, Arizona cottontail, antelope 
chipmunk, Merriam kangaroo rat, desert wood rat, Arizona grass- 
hopper mouse, Stephens white-footed mouse, long-tailed pocket 
mouse, and western bat. The rough-scaled lizard, fence lizard, 
and pallid rattlesnake were conspicuous reptiles. 
GENERAL CONSIDERATIONS. 
Birp PopuLATION AND Its Mopiryina INFLUENCES. 
In the coastal lowlands of southern California a condition 
manifests itself which has been commented upon several times, 
but which as far as I am aware has not been explained. I refer 
to the almost universal exodus in July of many of the birds of 
the ‘‘summer-vyisitant’’ category, which have bred and raised 
broods during April, May, and June. Such birds as the Bullock 
oriole, lazuli bunting, Parkman wren, California yellow warbler, 
black-headed grosbeak, and many others to a more or less extent, 
become scarce, or disappear altogether, towards the end of July. 
Even such ‘“‘resident’’ species as the California bushtit, Cali- 
fornia jay, black phoebe, Anna hummingbird, and others, are 
reduced in numbers, although they appear again in early winter. 
The reason for this early summer exodus seems plain: The 
months from July to October constitute the winter season at the 
lower altitudes in southern California as far as food supply is 
concerned. Everything becomes excessively dry; among plants 
most annuals have died, and the perennials have ceased active 
growth; insects become relatively rare, except along watercourses. 
The May bird population, which is abundant, cannot continue to 
be supported after this ‘‘winter’’ season sets in, and the result 
is, they must move elsewhere. 
This condition is without a parallel in eastern North Amer- 
ica; at least I have been unable to find recorded mention of it, if 
it exists. 
But where do our birds go? My three summer’s work in the 
San Bernardino mountains determined this to my own satisfac- 
tion. My field note-book, under date of August 2, 1906, contains 
