46 Motivation
defensive behavior may fall into a single category of preda-
tory imminence (e.g., freezing). However, the expression of
some behaviors (e.g., flight) may actually reflect several dif-
ferent components of defensive behavior that fall into differ-
ent categories.
Preencounter Defensive Behaviors
Animals display preencounter defensive behaviors in situa-
tions where a predator may be present but that predator has
not yet been detected.
Meal-Pattern Adjustment. A rat may be at higher risk
from predators when it leaves its burrow to forage for food.
One strategy that diminishes this threat is to reduce the num-
ber of foraging excursions by increasing the size of the meal
consumed on each trip. Indeed, when rats are housed in an en-
vironment that requires them to traverse a shock grid to for-
age for food, they modify the size and frequency of meals
taken in relation to shock density. Specifically, with increas-
ing shock density, rats take fewer, but larger, meals (Fanselow
et al., 1988).
Dark Preference. Rodents have a preference for dark
places. This behavior presumably has a defensive purpose
because rodents are less likely to be detected by predators
when they occupy a dark location (e.g., Valle, 1970). Rodents
may engage in this behavior in both preencounter and post-
encounter defensive situations.
Thigmotaxis. Rodents have a tendency to stay near
walls. This behavior contributes to successful defense be-
cause it limits the threat of attack from behind and because it
may also reduce the animal’s visibility (e.g., Valle, 1970).
Rodents may engage in this behavior in both preencounter
and postencounter defensive situations.
Burying. Rodents bury threatening objects when mate-
rials such as wood chip bedding or wooden blocks are avail-
able. For example, rats bury a metal rod that delivers shock to
the animal (Pinel & Treit, 1978). The specific purpose of this
behavior is disputed. Some investigators suggest that burying
is fear response akin to defensive attack of the shock prod
(Pinel & Treit, 1978). Other investigators have offered alter-
native explanations that describe burying as a manifestation
of preemptive nest maintenance directed at protecting the an-
imal from further attack (Fanselow, Sigmundi, & Williams,
1987). An interesting property of burying is that this behavior
typically emerges only after rats have engaged in other de-
fensive behaviors: Most rats freeze and flee before engaging
in burying. Thus, burying is not prominent when predatory
imminence is relatively high. It is also often directed at exits
as much as the shock source (Modaresi, 1982). Thus, it seems
likely that burying is a preencounter nest-maintenance be-
havior in rats. However, in some species, such as ground
squirrels, it represents a higher imminence nest-defense be-
havior (Coss & Owings, 1978).Stretch Approach. Stretch-approach behavior is promi-
nent when a rodent encounters a localizable noxious object,
such as a shock prod. In this situation, the level of predatory
imminence is ambiguous, and this behavior may be thought
of as a cautious exploratory behavior employed to collect in-
formation about potential threats. This elaborate behavioral
sequencebegins with the rat advancing slowly towards the aversive object
in a low, stretched posture. As it advances, the rat periodically
stops and leans forward towards the object [in a manner that]
carries the rat into the vicinity of the aversive test object, from
where it is able to sniff it, palpate it with its vibrissae, and occa-
sionally contact it with its nose. (Pinel & Mana, 1989, p. 143)Rodents exhibit stretch-attend to potential predators
(Goldthwaite, Coss, & Owings, 1990), to areas of the test ap-
paratus in which they have received shock (Van der Poel,
1979), and to objects that have been the source of an electric
shock (Pinel, Mana, & Ward 1989). Pinel and Mana (1989)
suggested that this behavior functions to provide information
about the potentially hazardous object or location and that ol-
factory and tactile information via the vibrissae are important
elements of this information gathering.Leaving and Entering the Burrow. Rats often display
stretch-approach behavior if there is some potential danger in
the environment. Alternatively, if the rat has already left the
burrow but remains nearby, a slight increase in predatory im-
minence will cause retreat to the burrow. This action is one
form of flight. Such retreats to the burrow may be accompa-
nied by freezing within the burrow (Blanchard & Blanchard,
1989). However, if the animal is far from the burrow, or the
increase in predatory imminence is greater, the animal will
enter a different stage of behavior, postencounter defense.Postencounter Defensive BehaviorsRodents engage in postencounter defensive behaviors when
preencounter defenses have failed and a threat has been de-
tected in the environment.Freezing. Frightened rats display freezing behavior.
This defensive behavior is prominent in but not exclusive to