24 AMMAL LIFE IS THE YOSEMITE 



mark. Occasionally the bird could be identified only a-s to its general 

 grouping, as "hawk." Species of very close resemblance were sometimes 

 grouped together in a joint entry; for example, the crowned sparrows 

 (Zonotrichia). The plus sign indicated that more were present than the 

 actual number entered : the birds could not be counted with certainty ; 

 flocking birds, for instance, frequently could not be counted accurately. 



At the close of the day or of the period of observation, we were accus- 

 tomed to transfer our censuses from the field sheet (more or less scribi)led. 

 in lead pencil) to our permanent notebooks. If but few species of birds 

 had been seen, these were entered seriatim with numbers of each observed, 

 and comments ; if a goodly census had been secured we entered the results 

 in more formal, tabular style, on special sheets printed for this pur- 

 pose (fig, 3). In either case, record was kept of exact time involved, 

 approximate distance covered, nature of territory traversed, and weather 

 conditions. 



Totals were computed, both of species and individuals. Comparisons 

 of these totals for different parts of the Yosemite region and for different 

 seasons have brought forth some interesting conclusions. Outstanding 

 among these generalizations are the following: The greatest bird popu- 

 lation, both summer and winter, is found in the Upper Sonoran Zone. Next 

 come the Lower Sonoran and Canadian zones. The Transition Zone ha-s 

 a fairly large population in summer, but its population drops far down 

 in winter. The Hudsonian has the sparsest summer population, except, 

 of course, for the Alpine-Arctic. The winter population below the snow 

 line consists more largely of seed and berry eaters than of insect feeders ; 

 the summer population everywhere contains a predominating proportion 

 of insect-eating birds. 



"We present below a series of censuses, selected from the more than 

 250 in our notebooks. The censuses given are chosen to illustrate, first, 

 the nature of the avifauna in various representative parts of the Yosemite 

 section, and, second, the marked changes in bird life taking place in 

 Yosemite Valley from season to season through the year. 



The series of censuses given for Yosemite Valley is more complete than 

 for any other station in the section. It begins at the height of the nesting 

 season with two censuses on se])arate days in two different parts of the 

 Valley, embracing widely different sorts of habitats (associations) an<l 

 consequently unlike assemblages of birds. The decline of song and general 

 activity at the end of the nesting sea.son is indicated in the census of 

 July 30. That for October 25 shows replacement of the summer visitants 

 by winter invaders. The censuses of December 10 and February 2i) show 

 how completely the Valley is deserted by birds with the advent of the 

 midwinter snows; there are scarcely one-fourth as many birds present 



