that anticipates further energy needs; heavy predawn feed-
ing presumably enabled the rats to last through the corre-
spondingly longer daylight hours during the summer. Rats,
however, can abandon nocturnality altogether when subject
to heavy predation. Fenn and Macdonald (1995) found that
a population of rats in a rubbish tip that was regularly vis-
ited by foxes at night reverted to a diurnal activity pattern.
Foraging behavior in rats is typically described as the
outcome of conflicting motivations between curiosity (neo-
philia)andcaution(neophobia,meaning “fear of the new”).
Being omnivorous is an undeniable asset when colonizing
new environments; rats are typically faced with a wide va-
riety of foods, some of which are palatable and others poi-
sonous. This feeding behavior results in conflicting selec-
tive pressures, known as “the omnivore’s paradox” (Rozin
1976) i.e., the benefits of exploiting new food sources ver-
sus the cost of being harmed by them. Rats have evolved
several mechanisms that help them in diet selection. (1) Rats
have developed the capacity to make the association be-
tween what they eat and how they feel several hours after-
ward (“long delay learning”; Garcia et al. 1966) thus en-
abling them to assess the metabolic consequences of the
food that they ingest, therefore avoiding poisonous items.
(2) Rats may be physiologically adapted to survive the oc-
casional mistake: recent findings concerning the rapid evo-
lution of enzymes responsible for metabolic detoxification
in rats (Rat Genome Sequencing Project Consortium 2004),
cytochrome P450 (Danielson 2002) may highlight a hith-
erto underestimated weapon in its armory to survive the
omnivore’s paradox. (3) Rats can learn from other individ-
uals in the colony. A large body of evidence (mainly from
the laboratory) indicates that feeding preferencesare so-
cially transmitted (reviewed in Galef, chap. 18 this volume).
Young juveniles follow their mother during her foraging
sorties, but food preferences can also be influenced at an
earlier age by their mother’s milk, as well as when adults by
the smell emanating from other individuals in the colony.
Rats are more likely to try new foods if they smell them on a
healthy individual— the “Demonstrator Effect”—(see Ber-
doy 1994 for evidence in a wild rat colony). While there is
no evidence that food aversionscan be socially transmitted,
a rat is more likely to avoid a novel food if, following in-
gestion, it finds itself in the presence of an individual that
is ill—“The Poisoned Partner Effect.” (4) Rats are cautious
(neophobic). In contrast to mice, which are generally re-
garded as neophilic, rats are often described as among the
most neophobic of mammals (fig. 32.4). Neophobia varies
between rat species (Cowan 1977), between wild and labo-
ratory strains where it has been partially bred out (Mitchell
1976; see also Berdoy 2002), and in the wild between pop-
ulations (Brunton and Macdonald 1996; Brunton, Mac-
donald, and Buckle, 1993; Quy et al 1992;). Neophobia
also varies between individuals (Cavigelli and McClintock
2003), and can be modulated by social factors (see Galef,
chap. 18 this volume).
House mice are also mainly nocturnal, though they of-
ten feed in daylight hours (Rowe 1981). House mice also
shift their activity rhythms and times of feeding depending
on season and climate. Much of the work on wild house
mice concerns their effects as commensals in terms of con-
sumption of and damage to grain stores (Rowe et al. 1963;
Jackson 1977; Stoddard 1979; Stenseth et al. 2003). The
issue of transmission of food preferences, so thoroughly
explored in rats by Galef and colleagues (Galef, chap. 18
this volume), has not been examined as comprehensively
in house mice, although they also show social transfer of in-
formation (Valsecchi et al. 1996; Choleris et al. 1997). Un-
like rats, house mice are typically described as neophilic384 Chapter Thirty-Two
Figure 32.3 Because rats are small, brown, nocturnal, and difficult to mark,
most detailed behavioral data of wild rats have been recorded in large outdoor
enclosures, such as this one near Oxford (UK) where rat colonies can be pre-
sented with problems that they would normally encounter in the wild, such as a
diverse and multigenerational environment and a dispersed food supply. Photo
by M. Berdoy.