Sylvatic Plague Studies, IX. Studies of the Microclimate of the California Ground Squirrel Burrow and Its Relation to Seasonal Changes in the Flea Population

Abstract

This study was instituted to learn more about the environment of fleas that infest the California ground squirrel Citellus beecheyi (Richardson). Two primary objectives were: (1) to study the relationship of burrow temperature to flea infestations of the squirrels and (2) to learn the temperatures that fleas of this important rodent reservoir of sylvatic plague are naturally exposed to during the immature stages of their life cycle and while they are off the host during their adult stage. Citellus beecheyi was chosen for the study because of its well-demonstrated importance in the maintenance of plague in the western part of the United States. -The microclimate of rodent burrows has been studied before, but usually the principal interest in the studies was not centered on the influence of these conditions on flea populations. The microclimate of the kangaroo rat in the hot, dry Arizona desert during the hottest season (Schmidt Nielsen and Schmidt Nielsen 1950) and of several desert animals in southwestern United States (Vorhies 1945) and the temperatures of gerbil burrows in the sandy semi-desert between the lower parts of the Volga and Ural Rivers (Rall 1939) have been described. Storer (1933) gave the dimensions of some burrows in California and described the colonial systems, and Linsdale (1946), in his excellent work on the natural history of this squirrel, discussed at some