Effect of light intensity on activity patterns of patagonian leaf-eared mice, Phyllotis xanthopygus

The effect of light intensity on activity was investigated in a study of ca ptive leaf-eared mice, Phyllotis xanthopygus. This nocturnal mouse lives in rocky outcrops but forages in open areas with little vegetative cover. Pri mary predators are raptors and canids, all of which are expected to have in creased hunting success under higher levels of moonlight. Because of this c orrelation between light intensity and predation risk, we predicted that in creased light intensity during the dark period would result in decreased no cturnal activity. Data were collected continuously for 3 days under varying light intensities and were analyzed using cosinor analysis to estimate par ameters describing the activity rhythm (mesor, amplitude, and acrophase). N umber of diurnal activity bouts increased after exposure to light intensiti es 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 sig nificantly lower mesor and amplitude estimates compared with those of mice in control conditions (0.0 lux). The acrophase also was significantly diffe rent between the control and the 2 treatment groups.