Measuring daily and seasonal patterns of activity is useful for understanding the ecological and evolutionary drivers of behavior. We used collar-mounted light loggers to examine how nest attendance in arboreal squirrels and aboveground activity in semifossorial ground squirrels are affected by weather-driven changes in thermoregulatory conditions. Activity of lactating red squirrels (Tamiasciurus hudsonicus) had a diurnal pattern showing 3 daily peaks of activity with time spent outside the nest increasing with increasing ambient temperature, but decreasing with increasing relative humidity and wind. Despite the persistence of daylight during midsummer in the arctic environment, female arctic ground squirrels (Urocitellus parryii) also exhibited diurnal activity patterns with time spent above ground each day decreasing in response to precipitation but increasing with increasing ambient temperature and incident solar radiation. On cooler days, ground squirrels exhibited a unimodal activity pattern. However, on warm days, ground squirrels spent less time above ground when solar radiation and ambient temperature were both at their daily maxima, which resulted in a bimodal activity pattern. Our results highlight the utility of light loggers as a cost-effective means of addressing questions related to foraging behavior, parental care, thermoregulation, energetics, and timing of activity in arboreal and semifossorial small mammals.