EFFECT OF LIGHT INTENSITY ON ACTIVITY PATTERNS OF PATAGONIAN LEAF-EARED MICE,PHYLLOTIS XANTHOPYGUS

Abstract

The effect of light intensity on activity was investigated in a study of captive leaf-eared mice, Phyllotis xanthopygus. This nocturnal mouse lives in rocky outcrops but forages in open areas with little vegetative cover. Primary predators are raptors and canids, all of which are expected to have increased hunting success under higher levels of moonlight. Because of this correlation between light intensity and predation risk, we predicted that increased light intensity during the dark period would result in decreased nocturnal activity. Data were collected continuously for 3 days under varying light intensities and were analyzed using cosinor analysis to estimate parameters describing the activity rhythm (mesor, amplitude, and acrophase). Number of diurnal activity bouts increased after exposure to light intensities similar to full moonlight (3.0 lux). Total activity of mice in middle (1.5 lux) and high (3.0 lux) light treatments was depressed as evinced by significantly lower mesor and amplitude estimates compared with those of mice in control conditions (0.0 lux). The acrophase also was significantly different between the control and the 2 treatment groups.