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Hyenas cooperate better than chimps, study finds

Sept. 30, 2009
Courtesy Duke University
and World Science staff

Spot­ted hye­nas may not be smarter than chimp­anzees, but a study in­di­cates the much-maligned, dog-like creat­ures beat out our ape rel­a­tives in co­op­er­a­tive prob­lem-solv­ing tests.

Cap­tive pairs of spot­ted hye­nas that needed to tug two ropes in un­ison to ob­tain some food co­op­er­at­ed suc­cess­fully and learn­ed the ma­neu­vers quickly with no train­ing, re­search­ers said. Ex­pe­ri­enced hye­nas even helped in­ex­pe­ri­enced part­ners do the trick.

A pair of cap­tive hye­nas co­oper­ate to get some food. (Im­age cour­tesy Chris­tine Drea)
Faced with si­m­i­lar tasks, chim­panzees and oth­er pri­ma­tes of­ten re­quire ex­ten­sive train­ing, and coop­era­t­ion may not be easy, said Chris­tine Drea, an ev­o­lu­tion­ary an­thro­po­l­o­gist at Duke Un­ivers­ity in Dur­ham, N.C.

Drea’s re­search, pub­lished on­line in the Oc­to­ber is­sue of the jour­nal An­i­mal Be­hav­ior, sug­gests so­cial car­ni­vores like spot­ted hye­nas that hunt in packs may be good mod­els for in­ves­ti­gat­ing co­op­er­a­tive prob­lem solv­ing and the ev­o­lu­tion of so­cial in­tel­li­gence. 

She per­formed the ex­pe­ri­ments in the mid-1990s but strug­gled to find a jour­nal that was in­ter­est­ed in non-pri­mate so­cial cog­ni­tion. “No one wanted an­y­thing but pri­mate cog­ni­tion stud­ies back then,” Drea said. 

“But what this study shows is that spot­ted hye­nas are more ad­ept at these sorts of coop­era­t­ion and prob­lem-solv­ing stud­ies in the lab than chimps are. There is a nat­u­ral par­al­lel of work­ing to­geth­er for food in the lab­o­r­a­to­ry and group hunt­ing in the wild.”

Drea and co-author Al­lisa N. Cart­er of the Un­ivers­ity of Cal­i­for­nia at Berke­ley ar­ranged to have pairs of spot­ted hye­nas put in a large pen where they faced a choice be­tween two iden­ti­cal plat­forms 10 feet high. Two ropes dan­gled from each plat­form. When both ropes on a plat­form were pulled down hard in un­ison—a si­m­i­lar ac­tion to bring­ing down large prey—a trap door opened and spilled bone chips and a sticky meat­ball.

The double-rope de­sign pre­vented a hy­e­na from solv­ing the task alone, and the choice be­tween two plat­forms en­sured that a pair would not solve ei­ther task by chance.

The first ex­pe­ri­ment sought to de­ter­mine if three pairs of cap­tive hye­nas could solve the task with­out train­ing. “The first pair walked in to the pen and fig­ured it out in less than two min­utes,” Drea said. “My jaw lit­er­ally dropped.”

Drea and Cart­er stud­ied the ac­tions of 13 com­bina­t­ions of hy­e­na pairs and found that they syn­chro­nized their tim­ing on the ropes, re­veal­ing that the an­i­mals un­der­stood the ropes must be tugged in un­ison. They al­so showed that they un­der­stood both ropes had to be on the same plat­form. Af­ter an an­i­mal was ex­perienced, the num­ber of times it pulled on a rope with­out its part­ner pre­s­ent dropped sharp­ly, in­di­cat­ing the an­i­mal un­der­stood its part­ner’s role.

“One thing that was dif­fer­ent about the cap­tive hy­e­nas’ be­hav­ior was that these prob­lems were solved largely in si­lence,” Drea said. Their non-verbal com­mu­nica­t­ion in­clud­ed match­ing gazes and fol­low­ing one anoth­er. “In the wild, they use a vo­cal­iz­a­tion called a whoop when they are hunt­ing to­geth­er.”

Hyenas have an un­pleas­ant re­pu­ta­tion as some­what dirty and cow­ardly sca­ven­gers, though in fact they often hunt live prey as well. Al­though they re­semble dogs, hy­enas are more closely re­lated to mon­gooses and civ­ets.

In sec­ond and third ex­pe­ri­ments, Drea found that so­cial fac­tors af­fect­ed the hye­nas’ per­for­mance in both pos­i­tive and neg­a­tive ways. When an au­di­ence of ex­tra hye­nas was pre­s­ent, ex­perienced an­i­mals solved the task faster. But when dom­i­nant an­i­mals were paired, they per­formed poor­ly, even if they had been suc­cess­ful in pre­vi­ous tri­als with a sub­or­di­nate part­ner.

“When the dom­i­nant fe­males were paired, they did­n’t play nicely to­geth­er,” Drea said. “Their ag­gres­sion to­ward each oth­er led to a fail­ure to coop­erate.”

When an an­i­mal un­fa­mil­iar with the feed­ing plat­forms was paired with a dom­i­nant, ex­perienced an­i­mal, the dom­i­nant an­i­mals switched so­cial roles and sub­mis­sively fol­lowed the lower-ranking, naïve an­i­mal, Drea said. Once the naïve an­i­mal be­came ex­perienced, they switched back.

It was­n’t a big sur­prise that the an­i­mals were strongly in­clined to help each oth­er ob­tain food, said Kay Ho­le­kamp, a zo­ol­o­gist at Mich­i­gan State Un­ivers­ity who stud­ies spot­ted hye­nas.

Re­search­ers have fo­cused on pri­ma­tes for dec­ades with an as­sump­tion that high­er cog­ni­tive func­tion­ing in large-brained an­i­mals should en­a­ble or­gan­ized team­work. But Drea’s study sug­gests so­cial car­ni­vores, in­clud­ing dogs, may be very good at co­op­er­a­tive prob­lem solv­ing, even though their brains are com­par­a­tively smaller.

“I’m not say­ing that spot­ted hye­nas are smarter than chimps,” Drea said. “I’m say­ing that these ex­pe­ri­ments show that they are more hard-wired for so­cial coop­era­t­ion.”

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Spotted hyenas may not be smarter than chimpanzees, but a new study indicates the much-maligned scavengers beat out our ape relatives in cooperative problem-solving tests. Captive pairs of spotted hyenas that needed to tug two ropes in unison to obtain some food cooperated successfully and learned the maneuvers quickly with no training, researchers said. Experienced hyenas even helped inexperienced partners do the trick. When confronted with a similar task, chimpanzees and other primates often require extensive training and cooperation between individuals may not be easy, said Christine Drea, an evolutionary anthropologist at Duke University in Durham, N.C. Drea’s research, published online in the October issue of the journal Animal Behavior, suggests social carnivores like spotted hyenas that hunt in packs may be good models for investigating cooperative problem solving and the evolution of social intelligence. She performed the experiments in the mid-1990s but struggled to find a journal that was interested in non-primate social cognition. “No one wanted anything but primate cognition studies back then,” Drea said. “But what this study shows is that spotted hyenas are more adept at these sorts of cooperation and problem-solving studies in the lab than chimps are. There is a natural parallel of working together for food in the laboratory and group hunting in the wild.” Drea and co-author Allisa N. Carter of the University of California at Berkeley arranged to have pairs of spotted hyenas brought into a large pen where they faced a choice between two identical platforms 10 feet high. Two ropes dangled from each platform. When both ropes on a platform were pulled down hard in unison—a similar action to bringing down large prey—a trap door opened and spilled bone chips and a sticky meatball. The double-rope design prevented a hyena from solving the task alone, and the choice between two platforms ensured that a pair would not solve either task by chance. The first experiment sought to determine if three pairs of captive hyenas could solve the task without training. “The first pair walked in to the pen and figured it out in less than two minutes,” Drea said. “My jaw literally dropped.” Drea and Carter studied the actions of 13 combinations of hyena pairs and found that they synchronized their timing on the ropes, revealing that the animals understood the ropes must be tugged in unison. They also showed that they understood both ropes had to be on the same platform. After an animal was experienced, the number of times it pulled on a rope without its partner present dropped sharply, indicating the animal understood its partner’s role. “One thing that was different about the captive hyena’s behavior was that these problems were solved largely in silence,” Drea said. Their non-verbal communication included matching gazes and following one another. “In the wild, they use a vocalization called a whoop when they are hunting together.” In second and third experiments, Drea found that social factors affected the hyenas’ performance in both positive and negative ways. When an audience of extra hyenas was present, experienced animals solved the task faster. But when dominant animals were paired, they performed poorly, even if they had been successful in previous trials with a subordinate partner. “When the dominant females were paired, they didn’t play nicely together,” Drea said. “Their aggression toward each other led to a failure to cooperate.” When a naïve animal unfamiliar with the feeding platforms was paired with a dominant, experienced animal, the dominant animals switched social roles and submissively followed the lower-ranking, naïve animal, Drea said. Once the naïve animal became experienced, they switched back. It wasn’t a big surprise that the animals were strongly inclined to help each other obtain food, said Kay Holekamp, a zoologist at Michigan State University who studies spotted hyenas. Researchers have focused on primates for decades with an assumption that higher cognitive functioning in large-brained animals should enable organized teamwork. But Drea’s study demonstrates that social carnivores, including dogs, may be very good at cooperative problem solving, even though their brains are comparatively smaller. “I’m not saying that spotted hyenas are smarter than chimps,” Drea said. “I’m saying that these experiments show that they are more hard-wired for social cooperation.”