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The Behavior System 131

behaviors are activated in turn, which produces a sequence of distinguishable motor acts.
For instance, one behavior may be responsible for eating while the others are responsible for
bringing the animal near food. In this case, eating is the consummatory behavior because
it serves to directly satiate the affiliated hunger drive when active. It is the last behavior
activated in a sequence simply because once the drive is satiated, the motivation for engaging
in the eating behavior is no longer present. This frees the animal’s resources to tend to other
needs. The other behaviors in the group are called appetitive behaviors. The appetitive
behaviors represent separate behavioral strategies for bringing the animal to a relationship
with its environment where it can directly activate the desired consummatory behavior.
Lorenz considered the consummatory behavior to constitute the “goal” of the preceding
appetitive behaviors. The appetitive behaviors “seek out” the appropriate releaser that will
ultimately result in the desired consummatory behavior.
Given that each behavior group is composed of competing behaviors, a mechanism is
needed to arbitrate between them. For appropriately persistent behavior, the arbitration
mechanism should have some “inertia” term which allows the currently active behavior
enough time to achieve its goal. If the active behavior’s rate of progress is too slow, however,
it should eventually allow other behaviors to become active. Some behaviors (such as
feeding) might have a higher priority than other behaviors (such as preening), yet sometimes
it is important for the preening behavior to be preferentially activated. Hence, the creature
must perform “time-sharing,” where lower priority activities are given a chance to execute
despite the presence of a higher priority activity.
Behavior Hierarchies
Tinbergen’s hierarchy of behavior centers (an example is shown in figure 9.1) is a more
general explanation of behavioral choice that incorporates many of the ideas mentioned
above (Tinbergen, 1951). It accounts for behavioral sequences that link appetitive behaviors
to the desired consummatory behavior. It also factors in both perceptual and internal factors
in behavior selection.
In Tinbergen’s hierarchy, the nodes stand for behavior centers and the links symbolize
transfer of energy between nodes. Behaviors are categorized according to function (i.e.,
which biological need it serves). Each class of behavior is given a separate hierarchy. For
instance, behaviors such as feeding, defending territory, procreation, etc., are placed at the
pinnacle of their respective hierarchies. These top-level centers must be “motivated” by a
form of energy—i.e., drive factors. Figure 9.1 is Tinbergen’s proposed model to explain the
procreating behavior of the male stickleback fish.
Activation energy is specific to an entire category of behavior (its respective hierarchy)
and can “flow” down the hierarchy to motivate the behavior centers (groups of behaviors).
Paths from the top-level center pass the energy to subordinate centers, but only if the correct