Data for Circadian activity in a folivorous ground squirrel: questions of entrainment and weather effects

Most studies regarding mammalian circadian rhythms have been focused on nocturnal rodents under laboratory conditions, with only a few papers on diurnal species. 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 S. fulvus remains immobile underground at sunrise and sunset light transitions and at night, suggesting that its cycles of light exposure are self-imposed. All squirrels exhibited a decrease in both motor and aboveground activity duration as the season progressed. It remains unclear which environmental cues they use to synchronize their biological clocks. Circadian activity patterns were similar between the sexes but varied with age. Juvenile squirrels displayed longer durations of aboveground and motor activity than adults did, likely owing to higher energetic needs. On cooler days, motor activity declined, while aboveground activity patterns seemed to be unaffected by ambient temperatures. On rainy days, both the onset and offset of aboveground activity shifted toward the evening, and squirrels spent more time 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. We propose that weather-driven shifts in activity of these folivorous rodents are related to their limited ability to cache food, and that generally, food caching by burrowing mammals modulates the effects of weather on their daily rhythms.