Optimum illumination for ground squirrel activity

The locomotor activity of four antelope ground squirrels was monitored in an activity-wheel enclosure at illuminance levels from 1.1 to 30000 lux and color temperatures from 1950 to 2860°K. The time spent running, speed of running, and length of non-stop running sessions were found to be sensitive to ambient light conditions. Time showed the greatest dependence and appears to peak between 1300 and 17000 lux, the latter value corresponding roughly to light conditions attained within 30 minutes after natural sunrise and before sunset. Running speed was influenced least but in the most highly consistent manner, appearing to peak between 2600 and 17000 lux. Session lengths were quite variable and showed the most complex changes with light level. The overall findings suggest that the squirrels also were influenced by color temperature. There were large individual differences in various aspects of the responses.