Lemurs Use Long-Term Memory, Social Cues and Smell to Locate Food, Study Finds

The striking and social lemur is native to Madagascar. Primarily herbivores, these wooly primates spend most of their time high up in tree branches eating fruit, leaves, bark, insects and other foods; resting; and raising their young.

A new study has found that lemurs use social cues, smell and long-term memory to find hidden fruit — strategies that may have long-established evolutionary roots.

“Our study provides evidence that lemurs can integrate sensory information with ecological and social knowledge, which demonstrates their ability to consider multiple aspects of a problem,” said Elena Cunningham, the study’s lead author who is an anthropologist and New York University (NYU) College of Dentistry professor of molecular pathobiology, in a press release from NYU.

Animals rely on a combination of their senses and social and environmental knowledge in locating food and water.

“Historically, there have been two schools of thought on why primates developed bigger brains: ecological pressures, such as needing to find scarce fruit in the forest, and the social pressures of living in a group where everyone is trying to outsmart one another,” Cunningham said in the press release. “I have long been interested in the interplay between social and ecological factors when it comes to cognition — it seems like a given that these would have evolved in relation to each other.”

Cunningham visited the Lemur Conservation Foundation in Florida — a reserve dedicated to protecting and researching the primates — to get a better understanding of how they integrate these factors to locate food.

Several lemur species live at the foundation, including brown lemurs, who eat mostly fruit and have a much keener sense of smell than humans.

“All of the lemurs come from the same genus – Eulemur – which are sometimes referred to as brown lemurs. Individuals came from four Eulemur species: mongoose lemurs, collared brown lemurs, common brown lemurs, and Sanford’s brown lemurs. In nature the species associate with each other and can hybridize – these lemurs are known for behavioral flexibility,” Cunnngham told EcoWatch in an email. “In some species females are consistently dominant to males and in other species dominance between males and females is not consistent: males are dominant in some groups and in other groups females are dominant. We also had some mixed-species groups.”

The researchers conducted experiments with pairs of brown lemurs and groups of three in which they hid pieces of cantaloupe inside cardboard takeout containers, then placed both empty and fruit-filled containers in the primates’ environments. They observed how the lemurs investigated then opened the containers, making note of their interactions.

“In a competitive situation, smell is not the fastest way if you know where the food is. Even going quickly from one container to the other would be faster,” Cunningham told EcoWatch.

Even though the empty containers outnumbered those containing cantaloupe, the lemurs did not have much trouble finding the fruit, with several factors seeming to be working together to achieve this.

“The lemurs are constantly watching each other. When they see another lemur approach a baited container, or open a container or eat cantaloupe, they go there,” Cunningham said.

The lemurs were quick to learn which of the containers had food inside, and were able to remember the location of those that held fruit days, weeks and months later. They approached fruit-filled containers with an accuracy of roughly 50 percent higher than chance, and opened the containers with cantaloupe in them 98 percent of the time, suggesting they used their keen sense of smell to find the fruit at close range.

“The first five trials were conducted after delays of two hours or one day. Their performance improved as they learned the locations of the baited containers. Then we increased the time between each trial: 1 day, 2 days, 3 days, 5 days, 7 days, 14 days. We also waited one, two, and four months between trials. The lemurs’ performance never got worse, no matter how long the delay,” Cunningham explained.

^{Elena Cunningham / New York University}

The researchers observed that social factors influenced the individual strategies the lemurs used to find the fruit. Some more egalitarian groups willingly shared their information and melon. In others that were more hierarchical, dominant members of the group took advantage of subordinates who discovered cantaloupe by helping themselves to the found fruit. The subordinates, who were more likely to discover the fruit, sometimes put their “finder’s advantage” to use by eating more of the melon.

“In egalitarian groups both lemurs may get a piece of cantaloupe (there were two pieces in each container). In hierarchical groups the dominant lemurs displace the subordinates at the containers,” Cunningham told EcoWatch. “There was a lot of variation in the behavior of individual dominant and subordinate individuals. Some dominants mostly followed subordinates and displaced them. Some dominants wanted to eat all the cantaloupe and found their own containers and displaced subordinates at baited containers. Subordinates had interesting strategies. Some always entered the enclosure first so they could eat as much cantaloupe as possible before the dominant lemur entered. On one occasion a subordinate threw cantaloupe on the ground when he saw the dominant approaching and got the cantaloupe later. Other subordinates rarely approached baited containers and ate very little cantaloupe.”

The study, “Brown Lemur (Eulemur spp.) Use of Olfaction, Memory, and Social Strategies to Obtain Cantaloupe,” was published in the International Journal of Primatology.

“What our study shows is that these three factors are all operating at the same time — the lemurs have memories of where the food is and they are considering olfactory information and social factors,” Cunningham said in the press release. “We still have much to learn about how this interplay and the evolution of cognition, but it’s important to look at these factors not in isolation, but in conversation.”

Could the results of the study be used to improve the conservation of lemurs and their habitat?

“Most important for the conservation of lemurs is protecting their habitats and not hunting them or capturing them to sell as pets or for use in biomedical research. But, the results of the study could inform reintroduction projects and provide ideas for enriching the lives of lemurs in captivity. I hope that understanding the complexity of lemur thinking may give lemurs more intrinsic value in the minds of humans and lead to greater consideration of their welfare,” Cunningham told EcoWatch.

How are lemur populations faring in the face of habitat destruction, hunting and climate change?

“All lemur species are in decline – so the time to protect them is now. In terms of the specific species in the study, the IUCN Red List categorizes common brown lemurs as vulnerable, Sanford’s and collared lemurs as endangered, and mongoose lemurs as critically endangered (the next category is extinct in the wild),” Cunningham said.

What can people do to help protect lemurs and ensure their populations survive and hopefully thrive in the future?

“There is so much people can do! People should lower their carbon footprints. One powerful way is by reducing the amount of meat and dairy we eat. People should shop sustainably. They should buy wood products that are certified by the Forest Stewardship Council (FSC),” Cunningham told EcoWatch. “They should never click on cute photos of primates who seem to be pets – primates are being hunted for internet content. Primates should never be pets and legislation has been introduced to outlaw private pet ownership: write to your representatives to support the Primate Captive Safety Act. Donate to the Lemur Conservation Foundation and other conservation organizations in the future.”