Predation risk influences differentially the foraging decisions of rod
ent species with different morphologies (body size and locomotion type
), Explanations for different foraging patterns have been derived larg
ely from the behavior of heteromyid rodents, and there is a lack of in
formation regarding the behavior of other rodent groups with different
morphologies. Nevertheless, the explanations are thought to be applic
able to other groups. In order to study the generality of hypotheses a
bout the effect of morphology on foraging ecology, I investigated the
foraging decisions of Chilean sigmodontine rodents (Muridae) in the la
boratory, experimentally manipulating nocturnal illumination (a surrog
ate of predation risk) and food distribution. Three coexisting rodent
species from the Chilean matorral were compared: two quadrupeds, one w
ith large body size (Phyllotis darwini) and another with small body si
ze (Abrothrix olivaceus), and one small species with bipedal escape be
havior (Oligoryzomys longicaudatus). The species did not differ in pat
ch utilization and food consumption in response to different food dist
ributions. However, there was an overall significant effect of illumin
ation on food consumption. When illumination was higher, A. olivaceus
and P. darwini increased food transportation to the refuge and decreas
ed patch consumption and total food consumption. They also increased s
ignificantly the number of trips between food patch and refuge. P. dar
wini showed the most cautious foraging behavior. O. longicaudatus was
insensitive to different conditions of illumination. It is argued that
a large body size and quadrupedal locomotion seem to confer higher se
nsitivity to nocturnal illumination. Bipedality may confer less vulner
ability to predation, and quadrupedal species show facultative central
-place foraging, diminishing a possible greater vulnerability to poten
tial risk, Former explanations for different foraging behaviors under
the risk of predation may not be as general as previously assumed. Thi
s study emphasizes the need to consider the particular features of the
system under investigation.