Date of Award:
Master of Science (MS)
Department name when degree awarded
David F. Balph
David F. Balph
A. W. Stokes
F. H. Wagner
This study documents the timing of seasonal events and associated changes in body weights of Uinta ground squirrels (Spermophilus armatus) that live at three different altitudes. The investigation provides detailed field data for biologists investigating circannual rhythms and hibernation in the laboratory.
Ground squirrels aroused and subsequently emerged from hibernation in an overlapping sequence: adult males first, followed by adult females, yearling females and yearling males. Within limits some climatic condition(s) delayed emergence and increased the overlap in emergence sequence. The duration of seasonal activities above ground averaged about 90 days for adult and yearling squirrels. Juveniles were active above ground for 60-70 days. Each summer, adult males and adult and yearling females immerged into estivation-hibernation about the same date. Yearling males immerged later and juveniles immerged last.
Adult and yearling squirrels gained body weight rapidly except for brief periods during reproduction. Males began to gain weight after the breeding season. Female weights started to increase immediately after emergence but leveled off during lactation. Juveniles gained weight steadily after emergence from the natal burrow. Mean body weights of squirrels leveled off late in the active season.
Seasonal activities and changes in body weights of Uinta ground squirrels were shifted back 6 weeks in time at higher elevations.
The annual cycle of Uinta ground squirrels appeared to be the result of an interaction between an endogenous timing mechanism and the immediate environmental conditions. Arousal from hibernation occurred about the same date each year and was probably under endogenous control. After arousal, exogenous factors acted to shorten or lengthen subsequent phases in the annual cycle. Later arousal of squirrels at high altitudes indicated that endogenous timing mechanisms of the species are entrained to the environmental conditions encountered at the respective altitudes.
Knopf, Fred L., "Annual Periodicity in a Free-Living Hibernator, the Uinta Ground Squirrel" (1973). All Graduate Theses and Dissertations, Spring 1920 to Summer 2023. 1497.
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