ASSESSMENT OF PREDATION RISK VIA ILLUMINATION LEVEL - FACULTATIVE CENTRAL PLACE FORAGING IN THE CRICETID RODENT PHYLLOTIS-DARWINI

It is well known that the risk of predation affects prey decision maki ng. However, few studies have been concerned with the cues used by pre y to assess this risk. Prey animals may use indirect environmental cue s to assess predation hazard since direct evaluation may be dangerous. I studied the assessment of predation risk, manipulated via environme ntal illumination level, and the trade-off between foraging and predat ion hazard avoidance in the nocturnal rodent Phyllotis darwini (Rodent ia: Cricetidae). In experimental arenas I simulated dark and full moon nights (which in nature correlate with low and high predation risk, r espectively) and measured the immediate responses of animals to flyove rs of a raptor model. Second, varying illumination only, I evaluated p atch use, food consumption, central place foraging, and nocturnal vari ation of body weight. During flyover experiments, animals showed signi ficantly more evasive reactions under full moon illumination than in m oonless conditions. In the patch use experiments, rodents significantl y increased their giving-up density and decreased their total food con sumption under moonlight. On dark nights, rodents normally fed in the food patch, but when illumination was high they became central place f oragers in large proportion. Moreover, the body weight of individuals decreased proportionately more during bright nights. These results str ongly suggest that P. darwini uses the level of environmental illumina tion as a cue to the risk of being preyed upon and may sacrifice part of its energy return to avoid risky situations.