Vocal Communication

People have always been eager to find things that set them apart from animals and made them NOT animals. Most of these things have turned out to not be true. Especially according to the older literature, only we are bipedal, are hunters, use tools, and have a high degree of parental investment. Only we have the large brains and the long period of infant care. These all turn out to be quantitative rather than qualitative differences. They're not absolute- just tendencies. Nonhuman primates do stand bipedally, they do hunt, and plenty of monogamous species have extensive male parental care. In fact in some species, males are more involved in parenting than in most human societies. Our brains are bigger but not that much bigger than some of the great apes. As far as tools go, chimps use tools; they have certain sticks for fishing for ants and termites, and they have special rocks that they use for cracking nuts- hammers and anvils. Although the extent of our technology is greater than other primates, the things that sets us apart the most is our use of language.

Other primates do use vocal communication, but our language is again a qualitative difference. It almost seems like it developed all of a sudden which is pretty unlikely. Primates vocalize quite a bit, but they don't do too much vocal interchanges, while we have conversations a lot. One of the most important features about human language is that it's open-ended; we can continue to learn vocalizations indefinitely and we have a grammar which lets us string the words together in a certain way and lets us make up new sentences that have never ever been said before but are still comprehensible for anyone who knows the language.

Unsuspected complexity in primate vocal communication

Although language is different from animal calls, things aren't as clearcut as we had previously thought. There are several dichotomies which were thought to separate human language from animal noises.

Early theories re: primate vocalizations

Reflexive vs voluntary
Animal communication signals are involuntary or reflexive- they can't control their response when presented with a stimulus.

Affective vs representational
Human language can be representational. We can refer to things which are outside of ourselves or distant in space and time, while animal communication is generally thought to be representative only of the animal's internal state. So an animal can vocalize about being frightened or about being about to attack, but can't represent external events or objects.

Genetically determined vs learned
Human signals are learned but animals' are not- they're just genetically determined. Clear example- birdsongs.

So human language isand animal sounds are
learnedgenetically determined
symbolicaffective (emotional)

This all was accepted for many years until it became possible to study animals' vocal signals more quantitatively- we weren't able to do that until the development of the spectrograph. That allowed scientists to look at the fine structure of sounds, and to compare and measure them. When people began doing that, the picture began to get more complicated. Steven Green was studying Japanese macaques and the first clue that things were complicated was his study.

Japanese Macaque coos

The coo is a common short-range vocalization between group members. It didn't seem to be restricted to any particular situation, but was just a noise that they made sometimes. He looked at spectrograms of the coos, divided them into different types, and realized that certain types happened during certain circumstances. This suggested that primate repertoires might be bigger than we had thought- and also that their calls were more context-specific than we had thought, which raised possibility that they might also be more representational than we had thought.

Now we'll go through each of the three dichotomies and look at the evidence for and against each.

Reflexive vs Voluntary

The first big break came when we found a species which had a lot more control over its vocalizations than we had previously thought. Peter Marler and his associates looked at chicken vocalizations and they looked at rooster alarm calls. They set up experimental conditions with the rooster and one other chicken, scared the rooster, and noted whether the frequency of alarm calls changed depending on who the other chicken was. When no one was there, they didn't do the call as much; when their mate was there, they did the alarm call more; and when another female was there, it was even more. If the calls were just reflexive, then you'd expect the frequency to be the same no matter who was around. They also did a similar study with a food call called "tidbitting", and found that if other males were present then roosters didn't do tidbitting, but they did when females were around.

In primates, there was plenty of anecdotal evidence showing that vocalizations were voluntary. For instance, this story from Goodall. Early during her study she used to provision the chimps by putting out bananas. Figan was an adolescent at this time. She gave him some bananas, he got all excited and began to jump around and hoot excitedly, and the older chimps came and took the bananas away from him. Later on, she again gave him some bananas, and he got excited and jumped around but he didn't make a sound. This time, he got to keep the bananas.

Also, when chimps go on border patrols and its' dangerous 'cause they might run into males from the other community, they get really quiet. They won't vocalize at all, suggesting that they are controlling their vocal behavior.

The first quantitative evidence on this was from John Mitani studying pant-hoots; the frequency of a chimpanzee's pant-hoots depends on who is nearby; he found that if a male's ally was nearby, then the male was more likely to call. This is more evidence that it's voluntary.

Affective vs Representational

Do calls only represent the caller's emotional state or do they represent outside things?

Vervet monkey alarm calls are the classic piece of evidence. They were seen to have different alarm calls for different predators- one for snakes, one for large terrestrial predators, and one for aerial predators. Seyfarth and Cheney recorded alarm calls, analyzed them, showed that they really were different, and did playback experiments which showed that monkeys actually behaved differently depending on the alarm call and would behave appropriately. If they heard a snake call, they would stand up on their hind legs and look around. If it was an eagle call, they would run down from the trees into the bushes. If it was a cat call, they'd run up into trees. Since these were playback experiments, they knew the monkeys weren't just responding because of the presence of the predator. They also were worried that maybe the monkeys were just responding to the level of arousal in the call, so they modified the calls, making them louder and longer (the usual parameters that are affected by increased excitement), but the monkeys still acted the same.

Another bit of work was done on rhesus macaques by Carl Bazulis. (Sp?) He looked not at alarm calls but at the screams that they use to call for help. Remember that the rank of a female or juvenile depends on the rank of its relatives. This is because the relatives will help in a fight. This guy looked at the screams they give when fighting and asking for help, and he found that there are five distinct types of screams. He found it wasn't just a matter of how aroused or how excited the individual was, but that the call gave clues as to the type of fight the animal is in- whether the opponent is a relative, is of higher or lower rank, and how severe a fight it is. So again, the calls seem to be pretty representational; they give information about things external to the caller.

Then they did playback experiments of the same calls when there were no fights going on. Of course they found that the individual's mother responded pretty quickly, but they also noticed that the other macaques, when they heard the sound, didn't turn towards the monkey whose call was being played back, but turned and looked at the mother! So that showed that the monkeys not only knew who was calling, but knew who its mother was.

Genetically Determined vs Learned

Most of what we know about learning in animal vocalizations is from studies on songbirds. The first clear evidence that birds learned their vocalizations was the demonstration of dialects in birdsongs; when you look at birds over a geographical range, you find that they have slightly different calls. They learn from hearing what the birds around them sound like, so they develop distinct dialects in different places. Also, there have been experiments in raising birds in isolation or raising them after they've been deafened, and they don't develop normal sounds. It has been documented how they do it- birds have a 'sensitive period' when they're nestlings during which they listen to the adult songs but don't sing. Then, after fledging, they'll begin practicing a 'subsong' which still doesn't sound normal but will eventually become tuned until it's a song that sounds like the one they heard when they were in the nest. If they don't hear their species' song during their sensitive period, then they don't learn it properly.

Looking for similar things in primates just hasn't worked. For instance, in squirrel monkeys, there have been studies done on individuals raised in isolation who nevertheless make normal squirrel monkey sounds when they're only 6 days old. Similarly detailed studies haven't been done on other species, however. Also, there hasn't been too much evidence of dialects in primates, but recently there was some evidence from Snowdon studying marmosets, saying that they had dialects.

There is also evidence now of dialects in chimps, discovered by John Mitani. He recorded chimp pant-hoots from Gombe and Mahale, and he found that when he did detailed structural measurements, he could statistically differentiate the differences. They were subtle and there haven't been follow-up measurements, so people are still taking chimpanzee dialects with a grain of salt. John Mitani also found that male chimps who hang around together tend to sound more like each other and the chimps who were the most variable in the structure of their panthoots were ones who hung around with the least number of same individuals. He calls this is 'fratboy' effect- guys who all hang out together sound alike.

Basically, however, there isn't a lot of learning involved in the production of vocalizations. However, they do learn how to use vocalizations and how to respond to them properly. For this, we go back to alarm calls in vervets. They looked at actual alarm calls in the wild, recording who gave what alarm call and what stimulated it. They broke it down by age and they found that infants give all three types of alarm calls but all at the wrong times. If an infant sees anything in the sky, it'll give eagle alarm calls- a falling leaf, a pigeon etc. As they grow older, they begin to make the calls more appropriately- only at birds, then only at large birds, then finally only at raptors. They seem to learn how to respond by looking at what others are doing. So there is learning involved in how to interpret and use sounds, but not in how to make the sounds.


So we will summarize where the field stands right now, but you must remember that it's all changing fairly rapidly as we're learning about it. It seems pretty clear that primate vocalizations are more voluntary than we thought, and more representational. Most species have never been studied, nor most calls, so we don't know exactly how representational they are. As far as learning goes, there seems to be some, but there doesn't seem to be substantial learning in the production of the sounds, which is a real gap between primates and humans. There is also no evidence of a grammar for primates.

This is also a bit puzzling because of the studies that have been done with teaching chimps and gorillas human languages like ASL, from which it's clear that they can learn a large vocabulary when the language is gestural but not when it's vocal. The question of grammar hasn't been studied directly, so there's not evidence for it or against it really. Based on how little we know about most species and most calls, we don't know whether they're representational and affective.

Basically, we have a lot to learn about primate vocalizations.