The Lion's Roar: More than Just Hot Air
by Jon Grinnell

Music filled the still night air. Somewhere out in the darkness of the plains below us lions roared, first one, then another, and finally a third, forming a raw chorus of overlapping, repetitive bellows. Closer, a night bird called, its sharp notes punctuating the end of the lion roars, while faintly in the distance a family of jackals howled and yipped. The night had awakened, and its creatures were proclaiming themselves to the world.

We stood near our parked vehicles on the slopes of Lion Kopje on the southern edge of Tanzania's Serengeti National Park, and looked north across the short-grass plains toward the edge of the woodlands twenty-some miles away. Lion Kopje ("kop-ee") was so named because on maps the arrangement of the granite boulders jutting from the hilltop looks like the paw print of a giant cat. It is near the heart of the Gol United pride's range. Three members of this pride roared again on the plains below us, and we listened to hear if any of the neighboring prides would answer. On a still night the sound of lions roaring can carry five miles or more and can serve as an acoustic signpost, proclaiming for all who would hear that these lions are owners of this land. Instead of a distant reply, though, the deep voice of a male lion rose from the rocks 50 yards behind us: "aaaouu, aaaouu, aaaouu," over and over, and loud enough to make the metal body panels of our vehicles vibrate sympathetically.

After some searching in the moonlight with our binoculars, we could just make out a solitary male climbing down the boulders and onto the grassy slope. He roared again as he walked toward our vehicles, and we watched, through the phosphorescent green world of night-vision goggles, as he strode regally past us, a short 20 yards away. It was Norm, one of the two males resident in the Gol United pride, roaring in response to the familiar sounds of his pridemates. He gave us a quick, suspicious glance, then disappeared down onto the plains, moving toward the Gol Uniteds below.

As I stood listening after Norm disappeared, I imagined the landscape of sound available to an informed listener. Did Norm know those were his pride companions roaring down below him, or did he think he was going to meet a challenger in his territory? Can wandering males listen to the nightly declarations of others and know which will attack if approached too closely? Can listeners tell male from female roars and the numbers of each? Can hopeful males listen to the roars of a female and tell if she's calling "come hither" or shouting "get lost"? These questions passed through my mind as I looked down on the darkened plains that had swallowed up Norm and where I knew other lions waited. With Karen McComb, an animal communication researcher from Sussex University in England, I spent the next two years working out the answers to some of these vexing questions. Some are still unanswered, known only to the lions themselves.

Probably the sound most of us associate with lions is the snarl of the MGM lion, a deep, dangerous sound accompanied by lots of teeth. But lion roars are really sequences of three distinct types of "elements." They start soft and low with moan-like "prelude" elements, escalate into high-energy "roar" elements that begin at a frequency of about 240 Hz and drop to around 120 Hz, the "aaaouu" of Norm, then end with "grunts"--staccato "huh, huh, huh"s. Being staccato, with sharp beginnings and endings, grunts make the caller easy to locate, and may have evolved for that function. The roar elements, containing the most energy, would have the potential for telling the most about the animal--its age, condition, size, and the like. I and my students are looking into that possibility now by analyzing recordings of Serengeti lions. But whatever patterns we find will have to be confirmed by the only true experts on roaring--the lions themselves.

The lions in the Serengeti are among the most intensively studied wild animals in the world. Since 1966, when George Schaller first began observing them, researchers have more or less continuously documented their lives, and have learned a good deal about the intricacies of lion society and reproductive biology. Since 1979, the research has been overseen by Craig Packer and Anne Pusey of the University of Minnesota, and it was with their support that I went to the Serengeti as a graduate student to find out why lions put so much energy into roaring. And energy they do put in! Norm could shake our cars from 30 yards away, be heard five miles away, and do this over and over again throughout the night. Why should he work so hard at being heard?

Lion Natural History

Lions are unusual in the extent of their social behaviors and are by far the most social of cats. Both males and females form cooperative groups. The females live in "prides" of related individuals and occupy a traditional territory that's handed down from one generation to the next. Males form "coalitions" that enter prides from elsewhere. Both males and females roar, and both sexes show extensive cooperation in territorial defense, hunting, and cub rearing. Females are born into prides in which they typically remain for their entire lives (though prides do occasionally split), and different prides compete with each other in territorial disputes. Males leave their natal prides when they become sexually mature at three to four years of age, or when a new male coalition moves into the pride, whichever comes first. Once out of the natal pride, male lions wander far and wide in search of food, females, and male companions, until they are old enough and have joined a large enough coalition to be able to take over a pride of their own and become "resident." (Photo by Marta Youth.)

The reproductive success of a male lion--as measured by the number of surviving offspring--depends primarily on his ability to gain and maintain access to a pride of females--the longer a male can remain with a pride, the more offspring he will be able to sire. But males on average are able to hold onto a pride for only two to three years, just the minimum amount of time to successfully rear one cohort of cubs. Most coalitions are evicted from their pride by a larger rival coalition. Once evicted, male groups are rarely able to become resident in a pride again. Competition for residence in a pride can be very intense, with larger groups dominating smaller ones in aggressive encounters, much like rival street gangs fighting over turf, only in this case the lions are fighting not for territory but for the females on it. The best predictor of success for a male is thus the size of his coalition; larger coalitions gain residence sooner, remain resident longer, and thus have more surviving cubs per male than do smaller coalitions. It's necessary, therefore, for a wandering male or pair of males to find companions.

Ownership

You might think that nomadic males in search of companions would roar to advertise themselves to other nomads. In fact, this doesn't seem to be the case. With the help of Karen, I observed males from seven different nomadic coalitions (often formed of just a single male) for from six to 48 hours straight, starting at night when they would be likely to roar. In 13 nights, we never heard a nomadic male roar. In contrast, when we followed resident males in 12 different coalitions, they roared at least once, and usually many times in 20 out of the 24 nights we spent with them. Additional observations also demonstrated that resident males only roar when they are on their own territory. So the first thing we can say about roaring in males is that it is a display of ownership that is only given by residents on their own territory. (This is probably true for females as well, although in their case they are born into territory ownership, and if they split from their natal pride will still roar to defend a subset of the original pride range.)

However, otherwise nomadic males do roar when they join up with a solitary female during her estrous period. (A solitary female is either the last survivor of her pride, or has left the pride for one reason or another.) I regularly spotted male lions on the plains during the wet season, probably following the migratory wildebeest and zebra, and they would associate with a solitary female until the herds moved on. While thus temporarily resident they would roar. But perhaps they knew that single females typically are unable to raise cubs to adulthood, for when the herds left, so did the males.

Infanticide

Without resident males or other females to help with protection, a female's cubs are vulnerable. When new males enter a pride they kill all the cubs too small to escape them. This is advantageous for the males because it ends a mother's investment in her cubs and brings her back into estrus on average eight months sooner than if she cared for her cubs until they became independent. Infanticide is decidedly not advantageous for females, however, and they have evolved a number of counter-strategies to avoid it. In fact, infanticide may be the driving force behind female sociality. Traditionally, lion grouping was explained by the advantages of cooperative hunting. However, studies by Craig Packer, Anne Pusey, and David Scheel demonstrated that groups of two or more females are far better at defending their cubs from potentially infanticidal males than are singletons, but are not better at hunting. In addition to forming groups capable of physically attacking strange males, females can minimize the risk of infanticide by moving away from the roars of strange males, and by avoiding new males that associate with other females in the pride.

Part of the work that Karen and I did together was to investigate the role of roaring in infanticide avoidance. We had seen that females and males roared to advertise their territory ownership to rivals of the same sex, and to recruit aid from distant companions. When Norm responded to the roars of the Gol Uniteds, he was both advertising his ownership of the roaring females, and communicating his location to the females out on the plains. But females with cubs are faced with a dilemma. Roaring may be a cheap alternative to fighting same-sex intruders, but if non-resident males are attracted to female roars, by roaring she could be luring males in to kill her cubs. We tested this idea with playback experiments.

Playback experiments involve playing the recorded roar of one lion (or more) over a loudspeaker to another lion (or group of lions). During our nightly watches we had amassed a veritable library of lion roars, so now we played some back to test our hypothesis. For each experiment, we placed the loudspeaker in some brushy cover 650 feet from our subject, wound out about 330 feet of speaker cable to position our vehicle away from the speaker, and at dusk played the roar sequence at a volume calibrated to be realistic (about 115 decibels at one meter). Then we videotaped the lion's response from the safety of our car, and analyzed his behavior from the tape. To test whether non-resident males were attracted to female, but not male, roars, we played the roar sequences of male and female lions to these males. Our first results showed convincingly that non-resident males would indeed approach the roars of females, but never those of males. Now we could test something more interesting: Can females, by roaring as a group, keep potentially infanticidal males from approaching them? We played both one- and three-female roars to non-resident males and found that these males were indeed far more likely to approach one female roaring than a trio. So it appears that by banding together, females benefit not only by being better able to defend their cubs in direct encounters with potentially infanticidal males, but also because by roaring together they minimize the chance that these encounters will occur at all.

Attracting Mates

However, females aren't always roaring "get lost" at potential suitors. As part of my research I tranquilized a number of male lions to take blood samples and to attach radio collars to aid in relocating them. Once, I immobilized a male in consort with an estrous female. I hadn't seen the two mating before this, but after the male was fast asleep the female decided it was time, and walked sinuously by his sleeping form, back and forth, her tail lashing her receptive scent under his nose. When after a few minutes of this he still hadn't responded, she walked off--one can only guess at her thoughts--and started roaring, even though it was midday and a highly unusual time for a lion to roar. She continued roaring until the male awoke from his drugged sleep and rejoined her. Why did she roar? Probably the simplest explanation is that since she was in estrus and her first male had lost all interest in her, she meant to attract a new one.

While roaring can attract males when females want them, females have more tricks for getting the males they want to sire and protect their cubs. Female lions, it turns out, may be good at inciting competition between male coalitions. It would be to a female's advantage to get as large a male coalition into her pride as possible, for a large coalition will tend to stay with the pride longer than a smaller one, and thus a female's cubs are more likely to have time to grow to adulthood safely. One way a female can incite competition between different coalitions is by sneaking off to mate with outside males when she comes into estrus. If she mates with non-resident males they will believe they are territory owners, start roaring, and draw the wrath of the true residents down upon them. If the new males are in a larger coalition than the old, a takeover may occur and the old males be driven off. In either case the female is likely to end up with the larger coalition. As long as her cubs are big enough to avoid the new males, she has little to lose. The only risk is that she could get pregnant by a male that is subsequently driven off, only to have her cubs, when they're born, killed by the eventual resident males. She minimizes this risk through a peculiarity of her fertility cycle: When mating with an unfamiliar male a female typically won't conceive for three months--plenty of time for the different coalitions to work out who stays and who goes!

Territoriality

With females possibly scheming against them, and rival males always ready to step into their shoes, resident males must be constantly vigilant to keep strange males out of the pride territory. Because males are resident with a pride for such a short period of time--two to three years on average--and rarely get a second chance at residence (and thus at reproductive success), it is worth it for them literally to fight to the death to defend their females and cubs. However, if there are cheaper ways to keep intruders out than fighting every one that wanders through, that's even better. Roaring is well suited to that function: it can be heard for miles, it proclaims the caller as a territory owner, and it informs the listener of the caller's sex and location. But there is a problem with roaring to keep rivals away--the problem of honesty.

Spoken intentions are notoriously unreliable. Most of us have experienced how easy it is to lie with words and tones of voices--types of vocal "signals." The problem with using words to convey information that must be believed, and with using vocal signals in general, is that they are too easily falsified. They are what researchers call "conventional" signals, meaning there is nothing to guarantee their honesty. In contrast, "assessment" signals are those such as body size or beards that tell something about an individual that cannot be faked. Thus to really convince a rival to stay away, a lion should use an assessment signal. He should (and often does) show up to demonstrate to the interloper how capable he, the legitimate owner, really is. After all, owner or not, any lion could proclaim himself one by roaring, and just because he roars doesn't mean that he really will attack an intruder. Or does it?

There are two ways that a conventional signal such as roaring can be made honest. The first is to convey information that cannot be faked--a password, for example; the second is to constantly call the bluff of liars. Lions seem to do both. As mentioned earlier, it's the size of the coalition that best determines the outcome of aggressive encounters between male groups: three will defeat two, four will defeat three, and so on. Members of a coalition often roar in group choruses in such a way that makes it obvious that they are roaring together and not in competition with each other. One lion will start the roar sequence; part-way through his companions will join in, usually one at a time; and the male that began the chorus will often end it as well, almost always contributing more grunt elements than do his companions. A consequence of this structure is the honest advertisement of group size: A group chorus cannot be imitated by an individual or by a smaller group, and is unlikely to be produced accidentally by roaring competitors.

Male lions also call the bluff of any roaring would-be resident. If an intruder roars inside an owner's territory, he is confronted, escorted away, or attacked. I confirmed the generality of this through a series of 40-some playback experiments in which I broadcast strange male roars to residents within their territory. In almost every case, the owner aggressively approached the speaker, looked around for the intruder, and only then started roaring himself. Since the entire genetic future of a male depends upon his remaining resident with a pride long enough for cubs he has sired to survive, it's in his interest to respond to intruders every time. If he ignores a challenge once and new males supplant him in the pride, all his offspring will be killed. So a resident male keeps his declaration of ownership and intent to defend the pride honest by consistently challenging any intruder that disregards his roar.

Battle-scarred Norm undoubtedly knew those were his pride females calling from the plains. Perhaps he could also hear which males from the neighboring prides were close to his territory that night, which female roaring by herself was in estrus, which females were simply looking for their companions, and where his partner Snag was from his voice in the darkness. As an observer eavesdropping into this acoustic world, I could make out only a tiny part of all that was proclaimed and heard. Warnings, welcomes, mate attraction and repulsion, declarations of ownership and of group size--they were all broadcast through the darkness that night on Lion Kopje. Resident lions roared and nomadic males made their way silently around them, jackals and hyenas proclaimed their own messages to the listening night, and I climbed into the back of my truck, happy to sleep in a world where wild things still roar.

Jon Grinnell is an assistant professor of biology at The College of Wooster in Wooster, Ohio. When not sorting out the functions of lion roars, he also studies the vocalizations of other animals such as red squirrels and eastern chipmunks.

(ZooGoer 26(3) 1997. Copyright 1997 Friends of the National Zoo. All rights reserved.)



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