OBSERVATION OF PLACENTOPHAGIA 549
to determine at this point whether those switches
were a result of the procedure that occurred in the
interval between Tests 1 and 2 or whether those rats
belonged to the extremely small group whose behav-
ior toward placenta is inconsistent (Kristal & Graber,
1976).
DISCUSSION
Virgin rats were given the opportunity to observe
rats that were giving birth, rats that were eating
donor placenta, or rats that were eating chow. Dur-
ing the observation session, the observer rats could
smell, see, and eat donor placenta or merely smell
and see it. The baseline response to the test chamber
and to the presence of other rats was also deter-
mined. The results indicated that: (1) having other
rats present, and being in the chamber, when pla-
centa was available produced a high incidence of pla-
Centophagia during the observation session; (2) when
placenta was available during the observation ses-
sion, observing parturition (and therefore placento-
phagia) or placentophagia alone, produced signif-
icantly more conversions of nonplacentophages to
placentophages than did observing a rat eating chow;
(3) the number of conversions produced by observing
a rat eating chow was not greater than that produced
by the baseline condition (rat only); (4) neither ob-
serving a rat giving birth nor observing a rat eating
donor placenta, whether or not placenta was avail-
able for the observer rat to eat, was effective in alter-
ing the rate at which the observer rat was induced to
behave maternally by constant exposure to pups; and
(5) concaveation did not produce a significant in-
crease in the proportion of placentophages beyond
that produced by the observation procedure.
The effects of the procedure on placentophagia
could be interpreted as a result of one or more of
three main processes: social facilitation—an increase
in some characteristic of a response (in this case, the
likelihood of a response) because of the presence of
other individuals (Dewsbury, 1978; Zajonc, 1965);
observational or exposure learning—the social trans-
mission of an acquired behavior (Galef, 1976, 1977;
Hall, 1980); or sensitization or desensitization to a
stimulus, brought about by constant or repeated ex-
posure to the stimulus (Kristal, 1980; Rosenblatt
et al., 1979). Although the present study was not
undertaken specifically to select among these pro-
cesses, but rather to demonstrate the existence of an
effect, some conclusions about the three processes
can be drawn.
None of the groups in the no-access condition, in-
cluding the baseline group, were susceptible to the
effects of social facilitation, since they could not en-
gage in placentophagia when other rats were present.
(We assumed that the effect of the novel chamber
was minimal, since placentophagia tests are often
conducted in novel environments in our laboratory
with little or no effect.) Furthermore, since the base-
line group observed stimulus rats that were not eating
anything, exposure learning was probably not taking
place. However, placenta was present, and the sight
and smell of it could have been having an effect on
the subject, but the results indicated otherwise; no
baseline-group nonplacentophages were converted
into placentophages by this experience. In the other
no-access groups, the combination of the presence of
placenta (for desensitization) and the stimuli for ex-
posure learning of placentophagia was insufficient
to convert a significant proportion of nonplacento-
phages to placentophages.
The baseline∕access group had the stimuli for de-
sensitization (the presence of placenta) and the stim-
ulus for social facilitation (an audience), but not the
stimulus for exposure learning. Although social facil-
itation was sufficient to cause a high proportion of
rats to eat during the observation session, desensi-
tization coupled with eating produced by social fa-
cilitation were not sufficient to cause those eaters
to become placentophages permanently; most did not
eat on the subsequent placentophagia test. Access-
group rats exposed to stimulus rats that were eating
something or giving birth were receiving the stimuli
for desensitization (all three groups), for social facil-
itation (all three groups), and for exposure learning
of placentophagia (part∕access and plac∕access groups
only). Since the part∕access and plac∕access groups
showed the greatest increase in proportion of pla-
centophages after the observation session, it seems
that exposure learning does have an effect when the
behavior observed can be practiced during the expo-
sure, and that some behaviors (e.g., placentophagia
in nonplacentophagic virgin rats) require social facil-
itation for initiation. That socially facilitated rats eat
placenta but do not necessarily become permanently
Placentophagic may partly explain why nonplacento-
phages eat placenta during parturition, yet unlike
virgin nonplacentophages that become placentopha-
gic after a stressful experience, do not necessarily
eat placenta when tested subsequently (Kristal, 1980;
Kristal & Graber, 1976; Kristalet al., 1981).
REFERENCES
Birch, H. G. Sources of order in the maternal behavior of animals.
American Journal of Orthopsychiatry, 1956, 14, 1-84.
Cosnier, J., & Couturier, C. Comportement maternal provoque
chez les rattes adultes castrees. Compte Rendu des Seances de
la Sociiti de Biologie, 1966,160, 789-791.
Dewsbury, D. A. Comparative animal behavior. New York:
McGraw-Hill, 1978.
Dixon, W. J., & Massey, F. J. Introduction to statistical analy-
sis. NewYork: McGraw-Hill, 1969.
Galef, B. G., Jr. Social transmission of acquired behavior: A