Eavesdropping (8 page)

I have discussed two perceptual targets, a sole individual and a dyad, or pair of individuals. The flow of information in these cases can either be
passive
, inasmuch as personal facts are “given off” because the actor is unaware (or does not care) that he is being
observed; or
active
, where information is “given” or donated by the actor to particular recipients, as in a dominance or courtship display.

This active-passive distinction refers to the sender. Where the receiver is concerned, personal information can be acquired
openly
or with
stealth
. Under the leaves, animals take steps to minimize or conceal certain activities, or to render them difficult to interpret. This makes it necessary for others to observe them
strategically
, or to interpret what they have seen and heard in a way that is socially shrewd. It is here that
theft
enters the picture.

The fact is that in the wild, animals constantly attempt to
outsmart
each other. One animal acts, hoping—if animals can hope—that no one will see him; another watches, in an effort to discover what it is that the actor wishes to conceal; then the eavesdropper reacts, hoping his reaction will pass unnoticed.

In studies conducted off the coast of Canada and Alaska, cetologists have discovered something interesting. Killer whales that feed on seals make fewer pulsed calls than whales that feed on fish. The reason, it is thought, is that the whales are vaguely aware that seals have better hearing than fish—which they do—and that any seals that are eavesdropping will be alerted by the calls and immediately swim for cover.
³⁰

In at least six avian species there is evidence for a
quiet song
, one that functions like human whispering. In one of the species, blackbirds, it’s called “twitter” song. This song has a number of acoustic features that limit its transmission, being higher-pitched, quieter, and more directional than ordinary song. Twitter song is sung by highly aroused males that are approaching or interacting with a conspecific at close range. In one of the classic conflations of sex and dominance, females are courted with twitter song and males are threatened with it. Female blackbirds also have a quiet song of their own. Known as the “copulation trill,” this song is acoustically different from the male twitter and is obviously used under different circumstances. Both twitters and copulation trills,
according to Torben Dabelsteen and his colleagues, are used when blackbirds have “a distinct need for privacy.”
³¹
These adjustments have the effect of preventing eavesdropping in others, but in some respects their use seems to be more furtive, perhaps “sneakier,” than eavesdropping itself. Why should efforts to prevent the theft of personal information involve
more
stealth than attempts to steal it?

For one thing, animal eavesdroppers rarely need to maneuver into position. Under the leaves, signals tend to carry. Animals often find themselves positioned to receive without any special maneuvering. But they still need to know what eavesdropping can tell them
about others
—this requires interpretive skill, a strategic mind. They also must deduce what their eavesdropping tells other animals
about them
. This means anticipating how some number of individuals will react if they have seen them—or not seen them—doing certain things. In fighting fish there is evidence that males who lose a fight are less likely, later, to court a female that was around at the time—and therefore was in a position to have witnessed their defeat—than one that was elsewhere.
³²

What about the females? Were the male losers right to assume that any females in the audience would actually have rejected them? I’m not sure the relevant experiment has been carried out with fighting fish, but in chickadees there is evidence that females who have seen their mate lose a song contest subsequently “divorce” him—researchers actually use that word—and cast about for some other male.
³³

It is adaptive, of course, for animals to conceal their interest in anything they would rather not share with others. When females become interested in a male, they may avoid detection by others of their sex, whose pulses may be similarly quickened at the sight. It also may not benefit a male to be seen approaching a female, for this may arouse the interest of other male suitors. This can be troublesome even if competitors find out what is happening later on. Marc Hauser noted that primates sometimes suppress a copulation cry
when others might hear them—like suppressing an orgasmic scream when visiting the in-laws.
³⁴

Perhaps one of the better ways to conceal possession of a valuable resource is to make off with it. In chimpanzees a male will occasionally form a consortship with a female and remove her from the group for a period of time. Jane Goodall wrote about one chimp, “Leakey,” who tried to abduct two females simultaneously (he ended up with neither). In extreme cases, consortships continue for several months. But the motive usually has more to do with the avoidance of hassle by sexual rivals than it does with romance—frequently, the females are browbeaten into compliance.
³⁵

By leaving the scene, chimps avoid interference and achieve successful sex, with no doubt about paternity. Since they also avoid detection when approaching food, and seek seclusion in their nocturnal nesting patterns, it will be tempting to ask, at some point, if what we are seeing in our closest evolutionary relatives is simply isolation or something that approaches what we call
privacy
. We will devote a great deal of thought to this later because fully fledged privacy, when it emerged in human societies, posed a whole new set of challenges and opportunities.

In the meantime, we have an “internal” issue that is nearly as important as privacy, and just as relevant to the acquisition of personal information by theft. This is deception, a cognitive aptitude that supports the ability of various species to play some form of hide and seek.

Consider the western scrub-jay, a species that stores food in hidden caches. These birds know when they are being watched. They continually relocate food that they have hidden previously if another jay is watching, relaxing these efforts if a barrier is placed between the cacher and the observer. They also hide food in faraway places if they can see that they are being monitored by another jay.
³⁶
Jays who customarily steal food themselves go to unusual lengths to hide their food, doing more to conceal it than an honest jay.
³⁷

The jays’ reaction to barriers raises questions about the role of secrecy and privacy in the animal kingdom, and the ability of animals to infer knowledge in other animals from acts of selective attention. This issue comes to the fore in the higher primates. Chimpanzees routinely follow each other’s gaze, and know what other animals can and cannot see. Implicitly, they appear to recognize that if another animal sees something, he has some awareness of that thing.

They use this information in devising strategies for acquiring food.
³⁸
When foraging, chimps prefer to approach food that is hidden from view, even if that means approaching it circuitously,
³⁹
and they also prefer invisible or silent approaches over ones that are transparent or audible.
⁴⁰
In an experiment by Juliane Bräuer and her colleagues, subordinate chimpanzees approached a banana that a dominant chimp was not in a position to see, in preference to one that was in the dominant animal’s line of vision.
⁴¹
These kinds of findings make chimps seem “sneaky” but of course they are merely behaving intelligently in competitive circumstances, and their goal, if they could be said to have a goal, is merely to get the food they need without being attacked.

Do any of these animals know what others are
thinking
? Under the right circumstances, chimps may be able to generate a crude inference or two, but it would be daring to assume that jays and fish can do this. Yet all these species seem to be aware, on some level, of the information that
would
be received by an eavesdropper
if
they were behaving in certain ways at the time that the eavesdropping occurred. We may underestimate the intelligence of animals if we ignore their ability to steal and conceal personal information.
⁴²
But the link between intelligence and deception is even more compelling, and more tangible. I mentioned earlier that in birds, scrounging species—kleptoparasites—have large brains for their body size. Chimpanzees may be more deceptive than any of the other higher mammals, and they also have very large brains for their body size. We humans are clearly the best liars in the animal
kingdom—even such laudable things as diplomacy and civility require “white lies”—and when adjustments are made for body size, we have the largest brains of all, especially in the cortical regions where acts of deception originate. We will discuss this further in a while, but there is another issue to consider before we take up the evolution of eavesdropping. It’s the size of animal groups.

To defend themselves against predators, solitary animals have to be vigilant. They must constantly swivel their heads like periscopes. This makes it hard to look for food, build nests, have sex, rear infants, and do anything at all in an undistracted manner. Clearly, something has to suffer under such an arrangement. Dik-diks and iguanas deal with this by outsourcing a portion of their vigilance to heterospecifics, as we have seen, and this surely makes good sense if one lives in a place where there happen to be airborne sentinels with a shared predator and a built-in disposition to issue audible warnings. But if no such species exists, and there are conspecifics nearby, would it not be wise to keep eyes and ears focused on
them
?

A century and a half ago the English geneticist Francis Galton spent some time observing wild oxen in the deserts of South Africa. These beasts, he noticed, tended to huddle together very tightly. They never gave any indication that they
liked
each other, but when something happened to separate them, the oxen became agitated. Galton surmised that herding reduces the probability of surprise attack. “To live gregariously,” he wrote, “is to be a fibre in a vast sentient web.” Merely by living in close proximity to others, Galton wrote, one becomes “the possessor of faculties always awake, of eyes that see in all directions, of ears and nostrils that explore a broad belt of air.”
⁴³

Galton’s idea has occasioned a great deal of research. A century later enough evidence had accumulated to justify a conclusion, and
it was that individual vigilance and probability of attack do indeed decline as group size increases.
⁴⁴
But there is a hitch, a serious hitch.

In apes and monkeys, groups have a typical size, ranging from as few as four to as many as twenty-five, and size matters. Groups—like dinner parties—can become too big, at least for certain purposes. If groups enlarge past the point of optimal monitoring efficiency, the new members can do little to provide additional protection, and just by existing they ramp up the competition for available resources.

Animals in larger groups interact more often than they do in smaller groups,
⁴⁵
and this increases the chance of friction. There is also more competition in larger groups. In primates, there is a constant struggle for power, and battles are fought over everything, especially food.
⁴⁶
Where groups have enlarged, the threat of predation was replaced, to some extent, by new fears of attack by conspecifics and, more ominously, members of one’s own social group. There is plenty of evidence that large-group apes are physically aggressive, even homicidal, particularly in the context of competition.
⁴⁷
The competition within primate groups “is so intense and potentially costly to reproductive success,” according to Brian Hare, who led much of the research on chimpanzee deception, “that it has been a challenge for behavioral ecologists to develop theories of why primates might live in groups at all.”
⁴⁸

With so much danger posed by one’s associates, it would not be surprising if group expansion caused a shift of attention from the periphery of an occupied space—the area
around
a group, the outer line of defense against predators—to the
center
of that space, literally the inner circle, and it appears that this is exactly what happened. Where
vigilance
had been the ancient and primary means of investigation, there was an evolutionary tilt toward
eavesdropping
.

There is no shortage of evidence that competition engenders eavesdropping. In one of the more elegant demonstrations, squirrel
monkeys—who live in large groups that are characterized by cliques, subgroups, and dominance hierarchies—were compared to cotton-top tamarins, which live in more egalitarian family groups known for cooperation, sharing, and relative peacefulness. The investigators found that the more competitive squirrel monkeys, as anticipated, devoted significantly more attention to other group members than the tamarins did.
⁴⁹

Within-group competition can create a tension between eavesdropping and vigilance. The time that animals devote to eavesdropping upon “their own kind” takes away from the time spent looking out for predators. There are some human issues here. Police departments that once were dedicated to crime fighting now must deal with terrorism as well.

When I have told friends that I was writing a book about eavesdropping, the men nodded, often without comment, but a number of women spontaneously declared—sometimes blushing—
“You must be writing about
me!” There are intriguing “gender” distinctions in our species, and we will take a good look at them in the chapters that follow. But it makes sense to look first at sex differences in the eavesdropping of other species. These will alert us to possible trends in the history of human eavesdropping, trends that go back nearly a thousand years.