<p>Recent chronobiological studies highlight the lifestyle-dependent variation and plasticity of mammalian circadian rhythms, underscoring the need for investigations in natural habitats. Here, we analyzed daily activity patterns of free-living yellow ground squirrels (<i>Spermophilus fulvus</i>) using telemetry. We decomposed their motor activity (rest/motion) and aboveground activity (in a burrow/on the surface) by combining data from light sensors and accelerometers. We confirmed that <i>S. fulvus</i> remains immobile underground during sunrise and sunset light transitions and at night. It remains unclear which environmental cues they use to synchronize their biological clocks. All squirrels exhibited decreases in both motor and aboveground activity duration as the season progressed. Circadian activity patterns were similar between the sexes but varied with age. Juveniles displayed longer aboveground and motor activity than adults, likely owing to greater energetic needs. On cooler days, motor activity declined and aboveground presence shortened, whereas on very hot days motor activity was not suppressed. Rain shifted the timing of aboveground activity and increased time spent underground during the daytime. Weather conditions increased variability of the light–dark and rest–activity rhythms in <i>S. fulvus</i>, thereby potentially affecting the entrainment of its internal clocks. In adult individuals, the decrease in aboveground activity began before day length shortened and was not associated with seasonal decreases in photoperiod or ambient temperature. We suggest that, while weather-driven shifts in the light-dark regime may disrupt circadian rhythmicity, photoperiod is unlikely the primary driver of pre-hibernation activity changes—a finding that warrants future investigation.</p>