Proceedings of the Vertebrate Pest Conference

As early as 1918, populations of the Oregon ground squirrel (Citellus oregonus Merriam) were reported to be increasing in northeastern California, presumably because of "the extensive clearing of the sagebrush and seeding of these clearings to grain and hay." Populations of this locally important field rodent have continued to increase since that time with the further development of agriculture. Observations of the author during the past quarter of a century indicate that ground squirrels in the most intensively farmed areas are changing their habits, and they may be evolving into an ecotype markedly dissimilar to that which existed in the pristine environment.