Q&A: Why Cy is Missing a Finger and Other Notes on Chimpanzee Aggression

Recently, we invited you to submit your questions. Joshua wanted to know: Why does Cy have only three fingers and a thumb on his left hand?

The short answer?

As far as we’ve been told, Rayne bit off or severely injured the third digit of Cy’s left hand at some point during their time at their previous home in California. As to why she did it (if the accusations are indeed true), we need to step back a bit.

Chimpanzees can be incredibly aggressive. And I don’t mean traumatized research chimpanzees can be aggressive or chimpanzees kept in captivity can be aggressive. I mean that natural selection has endowed all chimpanzees, to varying degrees, with a capacity for aggression and a tendency to utilize it to achieve certain ends. In other words, it’s a normal part of being a social chimpanzee—a tiny fraction of their overall behavior, to be sure, but an important one.

When discussing aggression in chimps, we typically differentiate between intergroup and intragroup aggression. Intergroup aggression, or the violence directed at chimpanzees in other communities, has the distinction of being far more lethal. These attacks, often the result of stealthy raids into neighboring communities, are understood to be part of an evolutionary strategy to guard or gain access to territory (and thus resources such as food or potential mates). Intragroup aggression, on the other hand, tends to be a way that chimpanzees—particularly late adolescent and adult males—determine rank or status within the community. Lethal aggression does occur within communities (often in the form of infanticide or the overthrow of the alpha male) but at about half the rate of that between groups.

It’s almost impossible to describe to someone who doesn’t work with chimps just how violent chimpanzee fights can be. Their strength, speed, and agility are literally superhuman. Their screams and cries are deafening. And they can be seemingly ruthless, quite often ganging up on more vulnerable chimps. While their muscular arms and legs are used to grapple and pin, their ultimate weapons of choice are their large teeth and powerful jaws, which open wide enough to accommodate most any body part of an intended victim—though they usually select ears, fingers, toes, and, in cases of more extreme violence, genitalia.

Life for captive chimpanzees is very different from that of their wild counterparts. They don’t have the same kind of territories to defend, nor do they have the potential to acquire new resources by raiding and killing. But natural selection doesn’t typically endow us with knowledge of why we behave the way we do; instead we’re simply primed to behave in ways that tended to benefit our ancestors (humans are no exception to this). And captive chimpanzees are often presented with situations that stoke those very same intergroup prejudices—most notably, during social introductions. When we are integrating groups—or even riskier, adding a single chimpanzee to an established group—we have to overcome that same hostility toward outsiders that drives wild chimpanzees to attack and kill their neighbors. And this is where we may see the most severe forms of aggression. At CSNW, it once lead to a conflict in which one participant, Honey B, had to have her toe amputated, and another, Burrito, had to be castrated due to the severity of the wound to his scrotum. Neither injury was lethal, though in Burrito’s case it was largely because of timely veterinary intervention. In a way you could say that we’re fortunate, because chimpanzees have died in similar circumstances at many accredited zoos and sanctuaries. These are the stories that don’t always make it to social media, but instead are shared by keepers and caregivers over drinks at a conference hotel bar, finding comfort in others that understand what it is like to work in this crazy field.

More often, we are witnessing the almost commonplace kind of aggression that serves to establish rank, form coalitions, and settle scores. Chimps, like humans, are status-seekers. Status may come with tangible benefits, but status itself is an intrinsic benefit, one that is apparently worth fighting for. Because this form of aggression serves to clarify relative dominance, we tend to see somewhat less of it in stable groups and more in groups that are newly formed, lacking a strong leader, or undergoing a leadership transition. It also appears to be more common in groups with unusual compositions (in terms of age, sex, etc.) or ones with chimps that lack social experience. Regardless, wherever there are two or more chimpanzees, there will be at least the occasional fight. One study at an accredited zoo found that their chimpanzees were wounded in fights ten times per year on average. Thankfully, along with their superhuman fighting abilities, chimps possess a superhuman ability to heal and an equally superhuman tolerance for pain.

Jamie’s group has been together for over 18 years now. You’d think that they would have achieved some level of stability after all this time. But they epitomize the problem with a lack of leadership and atypical rearing. When they arrived from the lab, we did a quick inventory of missing ears and digits: Negra was missing half an ear, Annie’s ear was torn almost in two, Burrito was missing a fingertip, Missy was missing most of a pinky, and Jody was missing toes (though at least one was said to have been severed by a guillotine cage door). Those are just the ones I can think of off the top of my head. We do the same inventory of every group that we rescue, and relatively few adult chimpanzees arrive at sanctuary with all ears and digits fully intact—unless they, like George, lived largely alone.

We’ve done our fair share of repairs and amputations here at the sanctuary, beyond those of Burrito and Honey B. One morning, the chimp house was perfectly still until a shriek erupted from Front Room 4. We looked over to see Burrito fleeing and Foxie sitting there in shock, a chunk of her ear laying on the bench beside her.

There’s a trap that I try to steer people clear of (and one that I have to try to avoid myself), which is to assume that every action that a chimpanzee takes is part of a grand Machiavellian drama; that each squabble is a deft maneuver towards some strategic aim. Did Burrito bite Foxie’s ear off because he wanted to outrank her? Was he trying to form an alliance with Jamie, who has positioned herself as Foxie’s chief antagonist? Possibly. That kind of thing certainly happens. But again, we have to bear in mind that the algorithm of natural selection has in many cases done most of the calculations for us in advance, and has left us with some rather dumb emotions to carry out all the work. Status might ultimately bring more food and more mating opportunities, but we start fights because we’re pissed. We overcompensate because we’re insecure. We anger others because we are socially inept. We gang up on the weak because we crave power. We ostracize those who are different because we want to belong. In other words, we can describe chimpanzee behavior in terms of ultimate causes, but as socially savvy as chimps are—and they are very savvy—the proximate cause for any given fight or injury is likely that they are bundles of emotions, both noble and ignoble, with the strength of several humans and teeth like railroad spikes.

As for Cy’s finger, I certainly don’t know what happened, but knowing him now, I’d be willing to place a bet: Rayne was going after someone she was mad at and Cy was injured trying to stop the fight. That’s the other thing about chimp fights, at least in captivity—they rarely end as they began and the chimp with the most injuries was probably not involved at the start.