CALIFORNIA SHRIKE 173 



taken. However, samples of the stomach contents of gambeli in win- 

 ter show it never takes as much as TO percent of vertebrate food. Both 

 Judd and Beal and McAtee have mentioned the fact that gaDibeli 

 seems to take fewer birds and mammals than do t]ie eastern races of 

 the species. This is believed to be dne to a more constant supply of 

 insects throughout the year in the range of gamljell in California. 

 Beal and McAtee estimate that vertebrate food during the entire year 

 amounts to onlj^ 12 percent in the western races, principally ganibeli. 



In the San Joaquin Valley of California small rodents occur in the 

 stomachs of shrikes more commonly late in summer than in winter. 

 At this season there is a flux in the populations of Reithrodontomys 

 and Perognathus in California. Specimens of gambeli taken about 

 alfalfa fields, grainfields, and orchards usually have captured no mice. 

 Contrasted with these conditions are those found in areas in the San 

 Joaquin Valley where the sparse native brusli is undisturbed, more 

 small rodents having been taken by the shrikes in these localities. 



Birds, chiefly small passerines, at no time comprise more than 15 

 percent of the food. 



Li regions where reptiles are common, these animals may amount to 

 7 or 8 percent of the diet. Some of the forms recorded as eaten or 

 impaled are : Ufa sp., Scelo'ponis sp., Cnemidophonis tessellatus, 

 Phrynosoma^ Gerrhonotus^ Diadophis, and ThamnopMs. Snakes as 

 long as 18 inches may be successfully attacked. 



Among the insects, the Orthoptera are variously estimated as con- 

 stituting 30 percent to 75 percent of the total food. The higher per- 

 centages recorded for insects of this order occur at the times of year 

 when grasshoppers increase to plague proportions. Bryant (1912) 

 concluded that grasshoppers at Los Banos, Calif., reached an abmi- 

 dance of 20 to 30 per square j^ard during a plague in July 1912. At 

 such times California shrikes were found to eat 47 percent of grass- 

 hoppers alone. Aside from the many species of grasshoppers and 

 locusts preyed upon by Lanius ludovicianus should be mentioned the 

 Gryllidae and Stenopelmatus. In California, Stenopelmatus is eaten 

 particularly during the rainy season when it may be encountered fre- 

 quently in fields or pasturelands. 



Members of the Coleoptera comprise only 20 percent of the bulk of 

 the food but are represented by a large number of individual animals. 

 Of the 20 percent, the Carabidae contribute 7 percent. 



In summarizing the factors that govern the kinds of food eaten by 

 shrikes, I should mention first the factor of the size of prey. Animals 

 too small to compensate for the energy expended by a shrike in procur- 

 ing them mark tho, lower limit of size. The maximum size of prey is 

 determined by the limits of the powers of the shrike to overtake and 

 kill large-sized animals. When large animals are available, these per- 



