Animal Learning & Behavior
1981,9 (4). 545-550
Observing birth and placentophagia affects
placentophagia but not maternal behavior
of virgin rats
MARK B. KRISTAL and J. KEN NISHITA
Slate University of New York at Buffalo, Amherst, New York 14226
To determine whether observing components of periparturitional behavior affects the mani-
festation of those behaviors in virgin rats, virgins selected for nonplacentophagia and for the
absence of spontaneous maternal behavior toward pups were exposed to stimulus rats that were
giving birth, eating donor placenta, or eating lab chow. During observations, subjects could
either eat donor placenta or just see and smell it. The subjects were tested subsequently for
placentophagia and for the rate of onset of pup-induced maternal behavior. The results indi-
cated that: (1) access to placenta in the presence of other rats led to placentophagia; (2) when
such placentophagia occurred in conjunction with exposure to other rats that were giving birth
or eating donor placenta, the subjects became permanent placentophages (otherwise, the sub-
jects reverted and did not eat on subsequent placentophagia tests); (3) none of the observation
conditions, regardless of the availability of placenta during observation, affected the maternal
sensitization latency. The results are discussed in terms of social facilitation, exposure learning,
and desensitization to exteroceptive stimuli.
Most virgin female rats do not eat placenta when
it is made available to them, yet virtually all parturi-
ent rats avidly consume placenta during delivery
(Kristal, 1980; Kristal & Graber, 1976; Kristal, Peters,
Franz, Whitney, Nishita, & Steuer, 1981). Stress-
ful events, including pregnancy, elevate the likeli-
hood of a rat’s eating placenta (placentophagia), al-
though not to the level of behavior observed during
parturition (Kristal et al., 1981). However, these
results were obtained in laboratory situations, which
typically use rats raised from weaning in relative iso-
lation from other rats engaged in normal life activ-
ities. Birch (1956) noted that fact regarding investi-
gations of maternal behavior, and his observation
remains true for most maternal behavior research
(Rosenblatt & Lehrman, 1963; Rosenblatt, Siegel,
& Mayer, 1979; Sturman-Hulbe & Stone, 1929;
Wiesner & Sheard, 1933). The normality of the ma-
ternal behavior exhibited by these relatively isolated
rats was evidence, according to Birch (1956), of the
irrelevance of social experience for the development
of maternal behavior. He added, furthermore, that
research results had shown “that rats are capable of
learning little or nothing from observing the behavior
of other rats” (p. 281).
Birch appears to have overstated the case. The
presence of conspecifics has now been shown to af-
The research was supported, in part, by Grant BNS76-O4316
awarded by NSF to Mark B. Kristal. We wish to thank Seymour
Axelrod for his helpful comments on an earlier version of this
manuscript.
Copyriglit 1982 Psychonomic Society, Inc. f
feet behavior—both indirectly, as in the case of social
facilitation (Dewsbury, 1978; Zajonc, 1965), and
more importantly for this discussion, directly, as in
the case of observational or exposure learning (Galef,
1976; Hall, 1980). The social transmission of infor-
mation seems particularly important when it relates
to feeding (Galef, 1977), and placentophagia is more
an ingestive behavior that is characteristic of ma-
ternal females than it is a maternal behavior, in the
sense of an infant-directed caretaking behavior. The
social environment may also have an effect by pro-
viding an exposure to stimuli which, in itself, is suf-
ficient to produce a gradual change in behavior to-
ward those stimuli. Repeated exposure to donor pla-
centa eventually causes virgins to stop avoiding it
(Kristal, 1980), and constant exposure to pups in-
duces appropriate maternal behavior in nulliparous
rats (see Rosenblatt et al., 1979, for a review).
That placentophagia and pup-directed maternal
behavior emerge apparently undiminished during
parturition in socially isolated laboratory rats may
be evidence of the unimportance of social experi-
ences, as Birch (1956) suggested, but it is not evidence
that social experience has no effect. The factors pro-
moting the full constellation of periparturitional be-
haviors are probably more than supramaximal at
parturition. Testing for the contribution of social ex-
periences may require the use of a preparation in
which the immediate, intense, hormonally based ver-
sion of maternal behavior is absent.
The present study was designed to investigate the
effect of observing parturition and placentophagia,
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