28 University of California Publications in Zoology. |Vou.5 
eround being gleaned over again and again, the birds resort to 
any other possible food source. 
A means of tiding over the season of greatest stress (in other 
words, of raising the number of birds which ean survive) is the 
storing up of energy during the preceding season of plenty. The 
majority of Audubon warblers in October and November, when 
they first appear around Pasadena, are excessively fat, and those 
taken at Bluff lake the first of September were already very fat. 
If the winter mortality of warblers were as great over other 
similarly wooded areas as it has been at times in my own door- 
yard in Pasadena, I have figured that in one season there were 
1280 deaths within the limits of this city alone. Most of these 
dead birds are promptly picked up by cats, so that they are not 
noticeable for long. 
We begin to see, then, what becomes of the bulk of the yearly 
increase. Of course there are other factors, such as enemies 
amone both birds and mammals: but these I deem of small ae- 
count (except locally) as a fundamental cause of death; for I 
thoroughly believe that it is the slowest, least alert bird in sight 
that is caught by the cat or hawk. And this bird is the one whose 
vitality is at a low ebb, and this is not liable to be a well-fed bird. 
There must be much variation in the individual ability of birds 
to secure an adequate living when food is searee. “And, by the 
process of natural elimination, it must be that species are be- 
coming more and more intensely developed in their food-getting 
ability, along the line of greatest advantage. 
SOME PLANTS OF THE REGION. 
The observer of animals must familiarize himself to some 
extent with the flora of the region in which he works. For the 
distribution and habits of practically all vertebrates, as well as 
of the lower animals, are so dependent on certain plants which 
are part of their environment that to pay attention to the ani- 
mals alone really means a very incomplete understanding of 
them. Neither should the botanist ignore the fauna of a region. 
The list of plants here presented ineludes only a very small 
