Annual and Season Weight Changes in a Thirteen-Lined Ground Squirrel Population, Itasca State Park, Minnesota

The ecology of the thirteen-lined ground squirrel (Citellus tridecemlineotus) has been under investigation since 1954 on the grounds of the University of Minnesota Forestry and Biological Station located in Itasca State Park, Minnesota. Over the 11-year period, data have been collected on individuals of this small, relatively isolated, population. Studies of population dynamics, movements, activity patterns, and weights have been stressed, chiefly during the three summer months of June, July, and August. In 1964, the senior author carried out field work for the entire season from April 30 to September 14