Life History of the Cascade Golden-Mantled Ground Squirrel (Spermophilus saturatus)

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Abstract
The life history of the Cascade golden-mantled ground squirrel, Spermophilus saturatus, was studied in a mixed habitat of forest and open meadow in Washington State from June 1980 to October 1982. Adult males and females emerged from hibernation in early May, yearling females in late May, and yearling males in early June. Time of emergence did not differ between habitats. Juveniles emerged from natal burrows from mid to late July in the meadow and from late July to early August in the forest. Adults and yearlings entered hibernation up to 45 days before juveniles. At least 51% of an individuals' time aboveground from May to September was spent sitting. Compared to ground squirrels in the forest, those in the meadow spent more of their foraging time eating (55% versus 42%), and had longer feeding bouts (53.2 versus 26.5 s) and shorter searching bouts (20.6 versus 33.6 s). Sixty-three percent of yearling females and 10% of yearling males were reproductively mature. Juveniles born in meadow habitat and that were recaptured 2 or more months after emergence moved farther than those in the forest (231.0 versus 54.8 m). Up to 60% of the residents in either habitat immigrated to the area from another location. Each age class weighed up to 15% more and adults and yearlings gained weight at a faster rate in the meadow than in the forest. These differences were not related to age structure, sex ratio, genotype, or time of emergence in the two habitats and most likely represented phenotypic response to food availability.