Jay Flock, © Steve Summers
in stable social groups requires a range of cognitive abilities,
including recognizing group members, tracking their social status,
and inferring relationships among them (Kummer et al., 1997; de
Waal & Tyack, 2003). Because the number of possible pairs of
individuals ("dyads") increases rapidly with group size,
members of large social groups cannot rely only on their own interactions
with other individuals to make relationship judgments. Transitive
reasoning should, therefore, be particularly important for social
species (Seyfarth & Cheney, 2003), but its use in making social
judgments had never been demonstrated in animals. Our experiment
Bond, Kamil & Balda 2004)
showed that highly social pinyon jays (Gymnorhinus cyanocephalus)
can draw sophisticated inferences about their own dominance status
relative to that of strangers simply by observing the stranger's
interactions with other, known individuals. These results provide
the first clear demonstration that animals use transitive inference
in social settings.
We captured sixteen adult male pinyon jays in northern Arizona and
housed them in individual cages in our animal care facility. For
this experiment, they were kept mildly hungry by controlling their
daily feedings. They were divided into three groups, two of six
birds each and one of four birds. Although some of the jays may
have known other members of their own group from the wild, the separate
groups were generally strangers to one another. To determine dominance,
we used a series of staged encounters between pairs of individuals.
The two birds were put into a plexiglas chamber with three compartments,
separated by opaque and transparent dividers (see illustration below).
At the start, each bird was placed by himself in one of the end
compartments with all of the dividers lowered. The central compartment
was baited with a single peanut (in the shell) that was glued to
a shelf to prevent either of the birds from carrying it away. After
10 seconds, the opaque dividers were lifted, so that the birds could
see each another and notice the presence of the peanut. After an
additional 10 seconds, the transparent dividers were also lifted,
giving the birds simultaneous access to the central chamber. Their
behavior for the next 5 minutes was recorded on digital videotape.
We repeated these encounter sessions six times for each dyad.
determined the dominance relationships for all pairs within each
of the three groups based on the frequencies of five types of behavior
during the encounter sessions -- one dominant display (Stare At)
and four submissive displays (Look Away, Crouch, Chin-up, and Beg;
Marzluff & Balda, 1992; Balda, 2002). Based on a subset of dyads
in which the dominance relationship was clear and consistent even
at the first encounter, we developed two measures, one of dominance
and the other of subordinance, that were weighted sums of the frequencies
of the five behaviors. The
difference between dominance and subordinance for a given individual
was an indication of its relative social status. Based on differences
in social status between individuals in all dyads in the sixth and
final encounter, we constructed dominance hierarchies for each of
the three groups and coded the bird designations accordingly. In
all three cases, the hierarchy was linear and fully transitive (Group
Group 2: 1>2>3>4>5>6,
and Group 3: P>Q>R>S).
For 62% of the dyads, stable dominance status was established by
the first or second encounter. Where both birds were low ranking,
however, the process often took much longer.
within-group dominance relationships had been established, we selected
eight of the 32 possible cross-group dyads and determined their
dominance relationships using the same staged encounter procedure.
These provided us with a basis for making predictions about relative
dominance across groups. To test the ability to draw social inferences,
we designated a set of birds as "observers," and allowed
them to watch a series of three-minute encounters between two other
birds. For each observer, all encounters involved a specific individual
from another group (the "demonstrator"). In each case,
the demonstrator was a stranger to the observer, but our cross-group
dominance tests indicated that the demonstrator should dominate
the observer if they were placed together in the encounter chamber.
On each of three consecutive days, observers watched their demonstrator
both lose an encounter with one opponent and win an encounter with
another. We used this balanced series of winning and losing encounters
to make sure that the observer would be making transitive inferences,
rather than simply responding to having seen another animal consistently
win or lose (Chase et al. 1994; Hogue et al. 1996; Oliveira et al.
up our encounters in a way that systematically controlled the observer’s
prior knowledge about one of the demonstrator’s opponents. In
experimental (EXP) sessions, the observer had information that would
allow him to make inferences from the demonstrator's wins and losses.
In control (CTL) sessions, the observer had no prior information about
the birds he was watching and could not make meaningful inferences.
During EXP sessions, the demonstrator and one of his opponents were
strangers to the observer, but the opponent that repeatedly lost to
the demonstrator was a familiar bird, one that had repeatedly dominated
the observer in earlier staged encounters. For example, suppose that
cross-group testing had established that B was dominant
to 2. We could then use 3 in an
EXP treatment by allowing him to observe A>B
and B>2 (see below). In this
case, A and B would be strangers
to 3, but the relationship 2>3
would have been established in earlier within-group interactions.
Using transitive reasoning, 3 should expect to be
subordinate to B.
during CTL sessions the demonstrator and both of his opponents were
all strangers to the observer. If 3 were assigned
to the CTL condition, he might watch A>B
and B>C, all strangers to him
(see below). Because he has no prior knowledge on which to base transitive
reasoning, 3 cannot predict his status relative to
the demonstrations, each observer was given test encounters with his
demonstrator (testing, in our example, B vs. 3), and the behavior
of both participants was evaluated for evidence of transitive social
inference. We conducted six sets of EXP and six sets of CTL demonstration
and test encounters, each using different observer/demonstrator dyads.
To avoid biases, dyads were assigned to treatments in a balanced fashion,
so that EXP and CTL dyads had the same average relative social status.
If EXP observers use transitive social inference to predict their
relationship to the demonstrator, they should, at least initially,
show higher levels of submissive behavior than CTL observers. That
prediction proved to be true. During the first minute of the first
test encounter, EXP observers showed submissive levels that were nearly
four times as high as those of CTLs (see below, left panel). Apparently
because of the initial submissive displays of EXP observers, EXP demonstrators
showed higher levels of dominance than CTLs during the second and
third minutes of the first encounter (see below, right panel). The
effects on both the observers and demonstrators were transient; there
were no significant differences in later encounters between the same
than just win/loss information was available to the observer birds.
The demonstration encounters also displayed the size of the disparity
between the demonstrator and his opponents. A strong, aggressive demonstrator
might dominate decisively in his winning contests and at least put
up a good showing in his losing ones. A weaker demonstrator, in contrast,
might barely show superiority in his winning contests and be utterly
submissive in his losing ones. Like critical fans at a prize fight,
observers could conceivably make more subtle, graded assessments of
the demonstrator. They could infer not just the direction of the status
difference between themselves and the demonstrator but how large the
difference probably was. To see whether observers made use of this
information, we calculated the level of dominance behaviors for each
demonstrator relative to both of his opponents and determined the
degree to which it predicted observer submissiveness during the first
test encounter. While there was a strong positive relationship for
EXP observers, there was no such relationship for CTL birds (see below).
This suggests that observers estimated the actual difference in their
dominance status relative to the demonstrator, but only when the losing
opponent was known to them.
agree with our prediction that pinyon jays should use transitive reasoning
to make inferences of relative dominance. Jays that had previously
interacted with one of the birds they observed drew inferences about
their rank relative to the demonstrator and showed a graded, quantitative
response based on their observations. Jays that observed very similar
interactions, but had never interacted directly with any of the birds
they observed, failed to show either effect. The treatment difference
rules out any alternative general explanations, such as badges of
status (Rohwer 1982) or simple motivational responses to seeing another
bird win or lose (Chase et al. 1994, Hogue et al. 1996, Oliveira et
al. 1998). This work constitutes the first demonstration of transitive
inference in social settings, and supports the hypothesis that social
complexity provided a crucial context for the evolution of cognitive
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