Ear Covering

Wild animals in captivity often exhibit behaviors not seen in the wild.  These are referred to as abnormal, undesirable, or stereotypical behaviors.  Captive great apes (orangutans, gorillas, chimpanzees, bonobos) share a variety of these behaviors, mainly regurgitation and reingestion of food (R&R) and coprophagy (eating feces), which really gross out the public.  Joe's R&R at Denver would often clear out the entire viewing area (which I appreciated)!  Coprophagy can lead to "fecal art," as the ape spreads out the feces to search for yummy undigested bits. Mountain gorillas sometimes exhibit coprophagy when confined to their nests while it rains, so this behavior doesn't officially classify as abnormal for gorillas. 

I view abnormal behaviors as adaptations to captive life.  For example, captive bears often pace in their exhibits, which reflects their tendency to patrol their large territories in the wild.  If you or I want more food, we can go to the kitchen or supermarket; captive apes cannot, but they can provide food for themselves via R&R and coprophagy.  Some captive gorillas also pluck their hair and nibble on the follicle at the base of the hair.  This may provide some sort of nutrition, but it is usually viewed as a way for a bored or stressed animal to self-stimulate.

While collecting behavior data on Maguba in Denver, I noticed that she sometimes would hunker down and cover her ears with her wrists, even resting in this position (photo at right).  This was in response to certain noises or when she seemed frightened or uncertain.  Once she covered her ears repeatedly as she was trying to touch silverback Joe, suggesting frustration.     

After I inquired on the internet and in various newsletters, I discovered that some members of all the great ape species exhibit ear covering.  (It has also been observed in humans, a fifth type of great ape.)  However, it appears to be particularly prevalent in captive gorillas, so in 1989 I began collecting data on ear covering by gorillas.  Gorilla field researchers told me that they had not observed this behavior in the wild (although it has been observed in African sanctuaries - see below), so ear covering does qualify as an abnormal behavior. My data set now includes the following:      

Zoo gorillas who cover their ears:  68 females, 31 males = 99.  Some of these gorillas have lived in multiple zoos.     

Zoos housing ear-covering gorillas:  77.  I have personally observed ear covering at 10 of these zoos. 

Countries where these zoos are located:  18.

Gorillas housed in African sanctuaries:  4 females, 3 sanctuaries, 2 countries.   

I asked respondents in what type of situations the ear covering tended to occur. The most common external events are loud/unusual noise, being shifted between rooms, conflict in the group, transfer to another group/zoo, loss of a group member, being separated from the group. For me, the most poignant is loss.  Six individuals began to cover their ears following the death of their mother or father.  Transfer and separation also underscore the importance for a gorilla of other group members.     

If you have visited zoos, I'm sure you have noticed how noisy the public can be. If glass separates the gorillas from the public, this reduces the noise level, but doesn't eliminate it.  One gorilla covered her ears less frequently after a sign was installed asking the public to watch quietly.       

I wondered how ear covering might change after a female gives birth and is busy with her baby (photos below).  Female gorillas with infants experience more respect and attention from the silverback and other group members, and their social status usually rises.  I did hear about three females who either stopped or decreased ear covering after giving birth.  Two females began to use their baby's hand(s) to cover their ears (photo below), and another female sometimes held her baby up to her ear!     

Respondents also mentioned the following internal states:  uncertainty, insecurity, frustration, anticipation, boredom, fear.  The most common response was that ear covering occurred when the individual was stressed.  The majority of these stress answers came from zoo keepers, who are the most familiar with the gorillas' moods.  A few gorillas who cover their ears also exhibit other stereotypic behaviors, such as hand waving, tongue wagging, or walking backward.     

Ear covering can include a variety of postures (see photos below), using a hand, wrist, finger, or shoulder.  A gorilla also might cover its ear with an object - an interesting intersection of ear covering and tool use, two of my areas of interest.

Someone once said to me - of course the gorilla would cover its ears when there is a loud noise. But if that's true, why does only one group member cover her/his ears?  For the most part, all group members are subjected to the same environmental stressors, so why don't they all cover their ears?  

Some of the gorillas in my data set were housed with another ear-covering gorilla, and thus could have learned the behavior.  The question remains - why didn't all group members begin to cover their ears?  Behaviors are usually only copied by individuals for whom the behavior is appealing or would be useful.     

Over half of the 103 gorillas in my data set are closely related to another ear-covering gorilla (parent/offspring, full/half sibling).  This certainly raises the possibility of a genetic component and inheritance of, for example, personality traits or sensitive hearing.  Over half of these related gorillas did not have the opportunity to observe and learn this behavior from their relative, due to not being housed together, supporting the genetic hypothesis.   

This brings up another potential variable.  Although this situation has improved, some captive female gorillas are not interested in or capable of raising their babies.  Therefore, some infant gorillas are raised by humans, which can result in behavior deficits.  However, in my data set more ear-covering gorillas were raised by their mothers than by humans.     

My conclusion is that ear covering provides a way for some gorillas to adapt to captive life by symbolically hiding from stressors.  Unlike gorillas in the wild, there is no other way for them to escape.  A major challenge of life in captivity is the inability of the animal to control its environment.  Ear covering can be a sign that all is not well with that individual.  Since not all gorillas exhibit this behavior, ear covering provides a way for caretakers to assess the psychological well-being of a captive gorilla.