Vol. XXVIII 

 1911 



J Grinnell, Range of the Mockingbird in California. 299 



berry-eating birds such as Western Bluebirds, Cedarbirds, and 

 Solitaires, all these being species which summer in the Transition 

 or Canadian zones. 



The Mockingbird is clearly very sensitive to temperature. It 

 must have warm summers, and warm winters as well. It is thus 

 similar in its demands to the orange tree. The popular notion 

 that it is by preference a bird of the orange grove, is based upon a 

 coincidence in the ecologic requirements of the bird and the plant, 

 and upon something more. While it does not appear that the 

 Mockingbird depends at all on the citrus tree for food, yet it is a 

 significant thing that the dense, stiff-twigged foliage of the orange 

 is most nearly like that of the small live-oak of the wash. And both 

 these trees are preferred above all others as sites for the nests of 

 the bird. 



While the Mockingbird of California is not a regularly migratory 

 species in any true sense, it is of interest to recognize the local and 

 partial seasonal movement in west central California. There 

 is an exodus in small numbers from the San Joaquin Valley into 

 the coast belt for the winter, when the former area is colder than 

 the latter; and the movement reverses in the spring when the 

 former is hotter than the latter. There is thus a longitudinal 

 shifting back and forth, though this involves only a fraction of the 

 population of the interior valley; this residual seasonal movement 

 is apparently due to shifting temperature conditions, again reflect- 

 ing the sharply defined temperature requirements of the bird. 



Summary. — The Mockingbird is essentially a non-migratory 

 species. It is restricted to a relatively small range in California 

 because of its evident extreme sensitiveness to temperature. It 

 adheres not merely to a zone of high summer temperature as do 

 many other non-migratory birds, but to a small portion of that zone 

 which also possesses a high winter temperature, above that of 

 severe frost. This combination of suitable summer and winter 

 conditions is found in the Lower Sonoran zone, in the San Diegan 

 district of southern California (northwest to Santa Barbara), and 

 in the bed of the San Joaquin Valley. Even in these restricted 

 belts the Mockingbird exhibits still further preferences dependent 

 upon plant association. It happens that the cultivated citrus 

 orchard satisfies the bird's predilections as regards the native asso- 



