Elephant Psychology
Content
Japanese Psychological Research 2009, Volume 51, No. 3, 177–181 Special issue: Comparative cognitive studies
doi: 10.1111/j.1468-5884.2009.00404.x Review
Elephant psychology: What we know and what we would like to know
NAOKO IRIE1* and TOSHIKAZU HASEGAWA University of Tokyo
jpr_404 177..181
Abstract: Although elephants are well-known and one of the most popular species among people, their behavior and cognitive abilities have not been studied very extensively. But recently, more and more researchers are becoming interested in studying their cognition, particularly their general intelligence, including causal reasoning and mirror self recognition, memory, and numerical cognition. Although genetically elephants are more closely related to the small-brained aardvarks and manatees than to primates, they hold enormous potential in their cognitive skills. Also, studying their cognition is important from the point of view of animal welfare in captivity. Key words: elephants, comparative psychology, causal reasoning, mirror self recognition, memory, numerical cognition.
At present, the three existing species of elephants, African savannah elephants (Loxodonta africana), African forest elephants (Loxodonta cyclotis), and Asian elephants (Elephas maximus), are all endangered. The African species and Asian species diverged approximately 7.6 million years ago, and the two African species diverged approximately 4 million years ago (Rohland, Malaspinas, Pollack, Slatkin, Matheus, & Hofreiter, 2007). All species of elephants are known to live a highly social life, quite similar to that of primates in some ways. Their society is a large network with hierarchical organization, which implies that elephants can deal with a degree of social complexity (Bates, Poole, & Byrne, 2008). Elephants live in groups of 3–100, consisting of related females and their calves. Herds are led by the oldest females, the matriarchs, to water and vegetation areas. The family members (the mother, aunts, and sisters) collaboratively raise
the calves. Mothers suckle their infants until they are approximately 5 years old. Females stay with their family for their whole life, while males leave the family to search for mates at the age of 12–15 years, when they are sexually mature. The males sometimes form a small group of 2–4 individuals. The elephants discriminate and recognize each other very precisely via visual, vocal, and tactile cues (Sukumar, 2001) and the matriarchs communicate with each other to decide their direction, and coordinate their movements using lowfrequency calls (Payne, Langbauer, & Thomas, 1986). Evidence of their capacity for vocal imitation, which is thought to be important in maintaining the bonds between individuals, has been reported (Poole, Tyack, Stoeger-Horwath, & Watwood, 2005). In the cases reported, a wild African elephant imitated truck sounds and a captive African elephant, who was living with two Asian elephants for 18 years, imitated the
*Correspondence concerning this article should be sent to: Naoko Irie, Department of Behavioral and Cognitive Science, Graduate School of Art and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan. (E-mail: [email protected])
1
We would like to thank Ueno Zoo, Ichihara Elephant Kingdom, Tennoji Zoo, Kyoto Zoo, and Asa Zoo for their understanding and participation in the elephant studies.
© 2009 Japanese Psychological Association. Published by Blackwell Publishing Ltd.
178
N. Irie and T. Hasegawa
chirping sound typically produced by Asian elephants, but not by African elephants. While many terrestrial mammals are able to learn to comprehend and use their calls correctly, there are only a few mammalian species that can modify their vocalizations in response to auditory experience (Janic & Slater, 1997). Although elephants are well-known and one of the most popular species among people, their behavior and cognitive abilities have not been studied very extensively. This might be because they are very dangerous animals to work with, both in captivity and in the wild, and because they have a very long life span, up to 70 years, and long-time observation is required. However, improvements in their management in zoos and the development of monitoring technology (i.e. satellite tracking system) have enabled researchers to start systematic studies with them. Here we will introduce some of the new views on the intelligence, memory, and numerical cognition of elephants, which recent studies have shown.
The intelligence of elephants
Elephants are generally believed to be highly intelligent. In several countries, elephants have been trained and tamed for public show and labor (Sukumar, 2001). Elephants easily learn to understand various sorts of commands that are verbally expressed by circus trainers and jungle dwellers (Rensch, 1957). Further evidence of elephant intelligence is their capacity to use tools. Hart, Hart, McCoy, and Sarath (2001) observed that wild and captive Asian elephants use sticks as tools to fend off flies and to scratch their own bodies (Hart & Hart, 1994). They reported that elephants sometimes modify sticks by breaking them into halves when they are too long, or by taking leaves off branches when they are too leafy (Hart & Hart, 1994). Because it was long believed that only a few species such as chimpanzees and crows spontaneously used tools in the wild (Gould & Gould, 1994; Hunt, 2000; Vauclair, 1996), the ability of elephants to use tools seems intriguing in terms of theoretical arguments about animal intelligence.
© Japanese Psychological Association 2009.
There is now a growing body of evidence demonstrating more sophisticated cognitive abilities in elephants. Recent studies have reported that elephants can recognize their own reflection in a mirror (Plotnik, de Waal, & Reiss, 2006), an ability once thought unique to only chimpanzees and orangutans (Povinelli, Rulf, Landau, & Bierschwale, 1993; Suarez & Gallup, 1981). Moreover, elephants can recognize means-end relations (Irie-Sugimoto, Kobayashi, Sato, & Hasegawa, 2008). This ability is equal to nonhuman primates, such as cottontop tamarins (Hauser, Kralik, & Botto-Mahan, 1999; Hauser, Santos, Spaepen, & Pearson, 2002) and chimpanzees (Povinelli, Reaux, Theali, & Giambrone, 2000). As noted above, elephants may possess highlevel cognitive abilities in various situations. Their intelligence potential is also supported by their anatomical features. Elephants have the largest brain of all terrestrial species (approximately 5000 g). Moreover, their encephalization quotient (EQ), that is, the ratio of cortex to body size, is high: 2.30, compared with 2.49 for chimpanzees and 7.44 for humans (Jerison, 1974). According to theoretical arguments, such a large brain is likely related to high cognitive performance (Jerison, 1974). However, Nissani (2006) reported the poor performance of elephants when given a causal reasoning task. In the task, the elephants were to simply remove the lid off a bucket to earn the bait inside, but some elephants still removed the lid when the lid was placed on the ground, and therefore unrelated to the goal of obtaining the bait inside the bucket. Nissani (2006) concluded elephants did not form a causal model in which the lid is perceived as an obstacle to the food underneath it. Still, it is possible that the results speak more to the rigidity of elephants’ learned behavior than to their lack of causal reasoning, as the author himself points out. Hart, Hart, and Pinter-Wollman (2007) argue that the lessdensely packed and larger elephants’ cortical nonsomatic neurons may account for their better performance in long-term extensive memory, but rather poor performance in conventional tests of cognitive performance, such as causal reasoning tasks.
Elephant cognition
179
Furthermore, elephants are unique in terms of possessing a prehensile trunk (Figure 1). The trunk makes it possible to manipulate easily various types of objects, even objects as small as a straw from a floor. Thus, in some ways an elephant’s trunk may be comparable with the skillful hands of primates. In addition, the highly mobile tip of the trunk, the length, and the ability to change the length of the trunk, make it possible for elephants to produce sounds at various frequencies. It is a well-known fact that elephants use low-frequency calls to communicate with individuals at more than 1 km away (Garstang, 2004).
correct drawing. When different pairs of drawings were presented, the elephant learned the discrimination more and more rapidly (within 10 trials by the fourth pair), and she managed to learn 20 pairs. Moreover she could select them even after a 1-year period. McComb, Moss, Sayialel, and Baker (2000) also showed that African elephants in the wild recognized the low-frequency calls of family members who had left the herd 12 years ago and who had died 24 months ago. She reported differences in the reaction of elephants when they were presented with calls of individuals with which they acquainted and those of unknown or unrelated individuals.
Memory
Although there is much anecdotal evidence indicating that elephants appear to be intelligent, not so much is investigated under the experimental environment. One seminal study examined to what extent Asian elephants possess the ability to memorize sets of arbitrary drawings (Rensch, 1957). In the study, a 5-year-old captive female elephant was presented with a pair of drawings and then required to choose the drawing that had been arbitrarily predetermined to be the ‘correct’ one. After several training sessions (330 trials in total), she had learnt to choose the
Numerical cognition
In our previous study, the results indicated that the numerical cognition ability of elephants might be superior to other animals that have been investigated, including nonhuman primates (Irie-Sugimoto, Kobayashi, Sato, & Hasegawa, 2009). We tested the relative numerousness judgment (RNJ) ability of nine Asian elephants. RNJ is the ability to discriminate two or more discrete quantities. In our first experiment, five elephants were simultaneously shown two baskets with differing quantities of bait (up to six items). In the second experiment, four elephants were sequentially presented with baits by dropping them one by one into two empty buckets (up to six items). In both experiments, the task of the elephants was to choose the larger quantity. The results showed that the elephants chose the larger quantity with significantly greater frequency, without any training to do so. The most intriguing point was that the elephants did not exhibit disparity or magnitude effects, in which performance declines with a smaller difference between the quantities in a two-choice task, or the total quantity increases, respectively. These findings appear to be inconsistent with previous reports of RNJ in other animals, for example, nonhuman primates including chimpanzees, whose performances show clear disparity and magnitude effects (Anderson,
© Japanese Psychological Association 2009.
Figure 1 The prehensile trunk of elephants (as seen on an elephant at Tennoji Zoo). It is used for grabbing, modifying other objects, greeting other individuals, and attacking.
180
N. Irie and T. Hasegawa
Stoinski, Bloomsmith, & Maple, 2007). The disparity and magnitude effects are explained by the accumulator model, in which animals are assumed to recognize numerosities or quantities using an accumulated analog representation without recognizing absolute numbers or labeling each separate object (Meck & Church, 1983). The performance of elephants cannot be explained by this model, suggesting that elephants might be using a different mechanism to compare and represent quantities than previously suggested for other species. This ability to judge the larger quantity may be adaptive for elephants from an ecological point of view, particularly with regards to their group structure. The size of elephant herds grows larger during rainy seasons and smaller during dry seasons (Sukumar, 2001). Elephants need to estimate the size of their own group or an approaching group, and changes in group formations across seasons, as well as to identify the numbers of females for mating. These ecological views might explain why elephants possess the advanced quantitative ability indicated by the study. Further investigation is required to clarify the precise mechanism underlying elephants’ numerical cognition ability.
with, as the adults weigh more than 4000 kg, and preventing accidents is of the greatest concern to the institutions. However, studying elephant cognition is also of urgent need today. The data have showed that elephants’ life expectancy is relatively low in captivity compared to the wild (Clubb, Rowcliffe, Lee, Mar, Moss, & Mason, 2008).This report might lead to the public opinion that elephants should not be kept in zoos and circuses. It is true that ensuring enough space for elephants’ playground and maintaining their physical health might be very difficult for many institutions, but by understanding the psychological and mental movement and cognition of elephants, keeping their mental health and keeping them happy in zoos is feasible. People have lived with elephants for a very long time, for example, the Myanmar logging industries and Thailand elephant camps. As the wild habitat is being threatened today, seeking for their welfare in captivity is important and urgent to save them from extinction. Therefore, the ideas gained from this basic research will play an important role in understanding elephants and their welfare.
References
Anderson, U. S., Stoinski, T. S., Bloomsmith, M. A., & Maple, T. L. (2007). Relative numerousness judgment and summation in young, middle-aged, and older adult orangutans (Pongo pygmaeus abelii and Pongo pygmaeus pygmaeus). Journal of Comparative Psychology, 121, 1–11. Bates, L. A., Poole, J. H., & Byrne, R. W. (2008). Elephant cognition. Current Biology, 18, 544– 546. Clubb, R., Rowcliffe, M., Lee, P., Mar, K. U., Moss, C., & Mason, G. J. (2008). Comprised survivorship in zoo elephants. Science, 322, 1649. Garstang, M. (2004). Long-distance, low-frequency elephant communication. Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 190, 791–805. Gould, J. L., & Gould, C. G. (1994). The animal mind. New York: Scientific American Library. Hart, B. L. & Hart, L. A. (1994). Fly switching by Asian elephants: Tool use to control parasites. Animal Behaviour, 48, 35–45. Hart, B. L., Hart, L. A., McCoy, M., & Sarath, C. R. (2001). Cognitive behaviour in Asian elephants:
Studying elephants
More and more researchers are becoming interested in studying the cognitive skills of elephants. This is hardly surprising, as studying elephants is an obvious challenge for cognitive scientists whose research has been concentrated on species that are phylogenetically close to humans, such as primates. Although, genetically, elephants are more closely related to the small-brained aardvarks and manatees than to primates, they hold enormous potentials in their cognitive skills. To conduct experimental research on elephants in captivity is very difficult, because keeping elephants concentrated on the task is hard as they are usually well-fed, and motivation towards baits is difficult to maintain. Also, elephants are very dangerous animals to work
© Japanese Psychological Association 2009.
Elephant cognition Use and modification of branches for fly switching. Animal Behaviour, 62, 839–847. Hart, B. L., Hart, L. A., & Pinter-Wollman, N. (2007). Large brains and cognition: Where do elephants fit in? Neuroscience and Biobehavioral Reviews, 32, 86–98. Hauser, M. D., Kralik, J., & Botto-Mahan, C. (1999). Problem solving and functional design features: Experiments on cotton-top tamarins, Saguinus oedipus oedipus. Animal Behaviour, 57, 565–582. Hauser, M. D., Santos, L. R., Spaepen, G. M., & Pearson, H. E. (2002). Problem solving, inhibition and domain-specific experience: Experiments on cotton-top tamarins, Saguinus oedipus. Animal Behaviour, 64, 387–396. Hunt, G. R. (2000). Tool use by the New Caledonian Crow Corvus moneduloides to obtain Cerambycidae from Dead Wood. EMU, 100, 109–114. Irie-Sugimoto, N., Kobayashi, T., Sato, T., & Hasegawa, T. (2008). Evidence of means-end behavior in Asian elephants (Elephas maximus). Animal Cognition, 11, 359–365. Irie-Sugimoto, N., Kobayashi, T., Sato, T., & Hasegawa, T. (2009). Relative quantity judgment by Asian elephants (Elephas maximus). Animal Cognition, 12, 193–199. Janic, V. M., & Slater, P. J. B. (1997). Vocal learning mammals. Advances in Study of Behavior, 26, 59–99. Jerison, H. J. (1974). Evolution of the brain and intelligence. New York: Academic Press. McComb, K., Moss, C., Sayialel, S., & Baker, L. (2000). Unusually extensive networks of vocal recognition in African elephants. Animal Behaviour, 59, 1103–1109. Meck, W. H., & Church, R. M. (1983). A mode control model of counting and timing processes. Journal of Experimental Psychology: Animal Behavior Processes, 9, 320–334. Nissani, M. (2006). Do Asian elephants (Elephas maximus) apply causal reasoning to tool-use tasks? Journal of Experimental Psychology: Animal Behavior Processes, 32, 91–96.
181
Payne, K. B., Langbauer W. R., Jr., & Thomas, E. M. (1986). Infrasonic calls of the Asian elephant (Elephas maximus). Behavioral Ecology and Sociobiology, 18, 297–301. Plotnik, J. M., de Waal, F. B. M., & Reiss, D. (2006). Self-recognition in an Asian elephant. Proceedings of the National Academy of Sciences of the United States of America, 103, 17053–17057. Poole, J. H., Tyack, P. L., Stoeger-Horwath, A. S., & Watwood, S. (2005). Animal behaviour: Elephants are capable of vocal learning. Nature, 434, 455–456. Povinelli, D. J., Reaux, J. E., Theali, L. A., & Giambrone, S. (2000). The support problem: Physical connection revisited. In D. J. Povinelli (Ed.), Folk physics for apes: The chimpanzee’s theory of how the world works. New York: Oxford University Press, pp. 254–270. Povinelli, D. J., Rulf, A. B., Landau, K. R., & Bierschwale, D. T. (1993). Self-recognition in chimpanzees (Pan troglodytes): Distribution, ontogeny, and patterns of emergence. Journal of Comparative Psychology, 107, 347–372. Rensch, B. (1957). The intelligence of elephants. Scientific American, 196, 44–49. Rohland, N., Malaspinas, A. S., Pollack, J. L., Slatkin, M., Matheus, P., & Hofreiter, M. (2007). Proboscidean mitogenomics: Chronology and mode of elephant evolution using mastodon as outgroup. PLoS Biology, 5, 1663–1671. Suarez, S. D., & Gallup, G. G. (1981). Self-recognition in chimpanzees and orangutans, but not gorillas. Journal of Human Evolution, 10, 175–188. Sukumar, R. (2001). The living elephants: Evolutionary ecology, behavior, and conservation. New York: Oxford University Press. Vauclair, J. (1996). Animal cognition: An introduction to modern comparative psychology. Cambridge, MA: Harvard University Press. (Received January 28, 2009; accepted May 16, 2009)
© Japanese Psychological Association 2009.
doi: 10.1111/j.1468-5884.2009.00404.x Review
Elephant psychology: What we know and what we would like to know
NAOKO IRIE1* and TOSHIKAZU HASEGAWA University of Tokyo
jpr_404 177..181
Abstract: Although elephants are well-known and one of the most popular species among people, their behavior and cognitive abilities have not been studied very extensively. But recently, more and more researchers are becoming interested in studying their cognition, particularly their general intelligence, including causal reasoning and mirror self recognition, memory, and numerical cognition. Although genetically elephants are more closely related to the small-brained aardvarks and manatees than to primates, they hold enormous potential in their cognitive skills. Also, studying their cognition is important from the point of view of animal welfare in captivity. Key words: elephants, comparative psychology, causal reasoning, mirror self recognition, memory, numerical cognition.
At present, the three existing species of elephants, African savannah elephants (Loxodonta africana), African forest elephants (Loxodonta cyclotis), and Asian elephants (Elephas maximus), are all endangered. The African species and Asian species diverged approximately 7.6 million years ago, and the two African species diverged approximately 4 million years ago (Rohland, Malaspinas, Pollack, Slatkin, Matheus, & Hofreiter, 2007). All species of elephants are known to live a highly social life, quite similar to that of primates in some ways. Their society is a large network with hierarchical organization, which implies that elephants can deal with a degree of social complexity (Bates, Poole, & Byrne, 2008). Elephants live in groups of 3–100, consisting of related females and their calves. Herds are led by the oldest females, the matriarchs, to water and vegetation areas. The family members (the mother, aunts, and sisters) collaboratively raise
the calves. Mothers suckle their infants until they are approximately 5 years old. Females stay with their family for their whole life, while males leave the family to search for mates at the age of 12–15 years, when they are sexually mature. The males sometimes form a small group of 2–4 individuals. The elephants discriminate and recognize each other very precisely via visual, vocal, and tactile cues (Sukumar, 2001) and the matriarchs communicate with each other to decide their direction, and coordinate their movements using lowfrequency calls (Payne, Langbauer, & Thomas, 1986). Evidence of their capacity for vocal imitation, which is thought to be important in maintaining the bonds between individuals, has been reported (Poole, Tyack, Stoeger-Horwath, & Watwood, 2005). In the cases reported, a wild African elephant imitated truck sounds and a captive African elephant, who was living with two Asian elephants for 18 years, imitated the
*Correspondence concerning this article should be sent to: Naoko Irie, Department of Behavioral and Cognitive Science, Graduate School of Art and Sciences, University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8902, Japan. (E-mail: [email protected])
1
We would like to thank Ueno Zoo, Ichihara Elephant Kingdom, Tennoji Zoo, Kyoto Zoo, and Asa Zoo for their understanding and participation in the elephant studies.
© 2009 Japanese Psychological Association. Published by Blackwell Publishing Ltd.
178
N. Irie and T. Hasegawa
chirping sound typically produced by Asian elephants, but not by African elephants. While many terrestrial mammals are able to learn to comprehend and use their calls correctly, there are only a few mammalian species that can modify their vocalizations in response to auditory experience (Janic & Slater, 1997). Although elephants are well-known and one of the most popular species among people, their behavior and cognitive abilities have not been studied very extensively. This might be because they are very dangerous animals to work with, both in captivity and in the wild, and because they have a very long life span, up to 70 years, and long-time observation is required. However, improvements in their management in zoos and the development of monitoring technology (i.e. satellite tracking system) have enabled researchers to start systematic studies with them. Here we will introduce some of the new views on the intelligence, memory, and numerical cognition of elephants, which recent studies have shown.
The intelligence of elephants
Elephants are generally believed to be highly intelligent. In several countries, elephants have been trained and tamed for public show and labor (Sukumar, 2001). Elephants easily learn to understand various sorts of commands that are verbally expressed by circus trainers and jungle dwellers (Rensch, 1957). Further evidence of elephant intelligence is their capacity to use tools. Hart, Hart, McCoy, and Sarath (2001) observed that wild and captive Asian elephants use sticks as tools to fend off flies and to scratch their own bodies (Hart & Hart, 1994). They reported that elephants sometimes modify sticks by breaking them into halves when they are too long, or by taking leaves off branches when they are too leafy (Hart & Hart, 1994). Because it was long believed that only a few species such as chimpanzees and crows spontaneously used tools in the wild (Gould & Gould, 1994; Hunt, 2000; Vauclair, 1996), the ability of elephants to use tools seems intriguing in terms of theoretical arguments about animal intelligence.
© Japanese Psychological Association 2009.
There is now a growing body of evidence demonstrating more sophisticated cognitive abilities in elephants. Recent studies have reported that elephants can recognize their own reflection in a mirror (Plotnik, de Waal, & Reiss, 2006), an ability once thought unique to only chimpanzees and orangutans (Povinelli, Rulf, Landau, & Bierschwale, 1993; Suarez & Gallup, 1981). Moreover, elephants can recognize means-end relations (Irie-Sugimoto, Kobayashi, Sato, & Hasegawa, 2008). This ability is equal to nonhuman primates, such as cottontop tamarins (Hauser, Kralik, & Botto-Mahan, 1999; Hauser, Santos, Spaepen, & Pearson, 2002) and chimpanzees (Povinelli, Reaux, Theali, & Giambrone, 2000). As noted above, elephants may possess highlevel cognitive abilities in various situations. Their intelligence potential is also supported by their anatomical features. Elephants have the largest brain of all terrestrial species (approximately 5000 g). Moreover, their encephalization quotient (EQ), that is, the ratio of cortex to body size, is high: 2.30, compared with 2.49 for chimpanzees and 7.44 for humans (Jerison, 1974). According to theoretical arguments, such a large brain is likely related to high cognitive performance (Jerison, 1974). However, Nissani (2006) reported the poor performance of elephants when given a causal reasoning task. In the task, the elephants were to simply remove the lid off a bucket to earn the bait inside, but some elephants still removed the lid when the lid was placed on the ground, and therefore unrelated to the goal of obtaining the bait inside the bucket. Nissani (2006) concluded elephants did not form a causal model in which the lid is perceived as an obstacle to the food underneath it. Still, it is possible that the results speak more to the rigidity of elephants’ learned behavior than to their lack of causal reasoning, as the author himself points out. Hart, Hart, and Pinter-Wollman (2007) argue that the lessdensely packed and larger elephants’ cortical nonsomatic neurons may account for their better performance in long-term extensive memory, but rather poor performance in conventional tests of cognitive performance, such as causal reasoning tasks.
Elephant cognition
179
Furthermore, elephants are unique in terms of possessing a prehensile trunk (Figure 1). The trunk makes it possible to manipulate easily various types of objects, even objects as small as a straw from a floor. Thus, in some ways an elephant’s trunk may be comparable with the skillful hands of primates. In addition, the highly mobile tip of the trunk, the length, and the ability to change the length of the trunk, make it possible for elephants to produce sounds at various frequencies. It is a well-known fact that elephants use low-frequency calls to communicate with individuals at more than 1 km away (Garstang, 2004).
correct drawing. When different pairs of drawings were presented, the elephant learned the discrimination more and more rapidly (within 10 trials by the fourth pair), and she managed to learn 20 pairs. Moreover she could select them even after a 1-year period. McComb, Moss, Sayialel, and Baker (2000) also showed that African elephants in the wild recognized the low-frequency calls of family members who had left the herd 12 years ago and who had died 24 months ago. She reported differences in the reaction of elephants when they were presented with calls of individuals with which they acquainted and those of unknown or unrelated individuals.
Memory
Although there is much anecdotal evidence indicating that elephants appear to be intelligent, not so much is investigated under the experimental environment. One seminal study examined to what extent Asian elephants possess the ability to memorize sets of arbitrary drawings (Rensch, 1957). In the study, a 5-year-old captive female elephant was presented with a pair of drawings and then required to choose the drawing that had been arbitrarily predetermined to be the ‘correct’ one. After several training sessions (330 trials in total), she had learnt to choose the
Numerical cognition
In our previous study, the results indicated that the numerical cognition ability of elephants might be superior to other animals that have been investigated, including nonhuman primates (Irie-Sugimoto, Kobayashi, Sato, & Hasegawa, 2009). We tested the relative numerousness judgment (RNJ) ability of nine Asian elephants. RNJ is the ability to discriminate two or more discrete quantities. In our first experiment, five elephants were simultaneously shown two baskets with differing quantities of bait (up to six items). In the second experiment, four elephants were sequentially presented with baits by dropping them one by one into two empty buckets (up to six items). In both experiments, the task of the elephants was to choose the larger quantity. The results showed that the elephants chose the larger quantity with significantly greater frequency, without any training to do so. The most intriguing point was that the elephants did not exhibit disparity or magnitude effects, in which performance declines with a smaller difference between the quantities in a two-choice task, or the total quantity increases, respectively. These findings appear to be inconsistent with previous reports of RNJ in other animals, for example, nonhuman primates including chimpanzees, whose performances show clear disparity and magnitude effects (Anderson,
© Japanese Psychological Association 2009.
Figure 1 The prehensile trunk of elephants (as seen on an elephant at Tennoji Zoo). It is used for grabbing, modifying other objects, greeting other individuals, and attacking.
180
N. Irie and T. Hasegawa
Stoinski, Bloomsmith, & Maple, 2007). The disparity and magnitude effects are explained by the accumulator model, in which animals are assumed to recognize numerosities or quantities using an accumulated analog representation without recognizing absolute numbers or labeling each separate object (Meck & Church, 1983). The performance of elephants cannot be explained by this model, suggesting that elephants might be using a different mechanism to compare and represent quantities than previously suggested for other species. This ability to judge the larger quantity may be adaptive for elephants from an ecological point of view, particularly with regards to their group structure. The size of elephant herds grows larger during rainy seasons and smaller during dry seasons (Sukumar, 2001). Elephants need to estimate the size of their own group or an approaching group, and changes in group formations across seasons, as well as to identify the numbers of females for mating. These ecological views might explain why elephants possess the advanced quantitative ability indicated by the study. Further investigation is required to clarify the precise mechanism underlying elephants’ numerical cognition ability.
with, as the adults weigh more than 4000 kg, and preventing accidents is of the greatest concern to the institutions. However, studying elephant cognition is also of urgent need today. The data have showed that elephants’ life expectancy is relatively low in captivity compared to the wild (Clubb, Rowcliffe, Lee, Mar, Moss, & Mason, 2008).This report might lead to the public opinion that elephants should not be kept in zoos and circuses. It is true that ensuring enough space for elephants’ playground and maintaining their physical health might be very difficult for many institutions, but by understanding the psychological and mental movement and cognition of elephants, keeping their mental health and keeping them happy in zoos is feasible. People have lived with elephants for a very long time, for example, the Myanmar logging industries and Thailand elephant camps. As the wild habitat is being threatened today, seeking for their welfare in captivity is important and urgent to save them from extinction. Therefore, the ideas gained from this basic research will play an important role in understanding elephants and their welfare.
References
Anderson, U. S., Stoinski, T. S., Bloomsmith, M. A., & Maple, T. L. (2007). Relative numerousness judgment and summation in young, middle-aged, and older adult orangutans (Pongo pygmaeus abelii and Pongo pygmaeus pygmaeus). Journal of Comparative Psychology, 121, 1–11. Bates, L. A., Poole, J. H., & Byrne, R. W. (2008). Elephant cognition. Current Biology, 18, 544– 546. Clubb, R., Rowcliffe, M., Lee, P., Mar, K. U., Moss, C., & Mason, G. J. (2008). Comprised survivorship in zoo elephants. Science, 322, 1649. Garstang, M. (2004). Long-distance, low-frequency elephant communication. Journal of Comparative Physiology A: Sensory, Neural, and Behavioral Physiology, 190, 791–805. Gould, J. L., & Gould, C. G. (1994). The animal mind. New York: Scientific American Library. Hart, B. L. & Hart, L. A. (1994). Fly switching by Asian elephants: Tool use to control parasites. Animal Behaviour, 48, 35–45. Hart, B. L., Hart, L. A., McCoy, M., & Sarath, C. R. (2001). Cognitive behaviour in Asian elephants:
Studying elephants
More and more researchers are becoming interested in studying the cognitive skills of elephants. This is hardly surprising, as studying elephants is an obvious challenge for cognitive scientists whose research has been concentrated on species that are phylogenetically close to humans, such as primates. Although, genetically, elephants are more closely related to the small-brained aardvarks and manatees than to primates, they hold enormous potentials in their cognitive skills. To conduct experimental research on elephants in captivity is very difficult, because keeping elephants concentrated on the task is hard as they are usually well-fed, and motivation towards baits is difficult to maintain. Also, elephants are very dangerous animals to work
© Japanese Psychological Association 2009.
Elephant cognition Use and modification of branches for fly switching. Animal Behaviour, 62, 839–847. Hart, B. L., Hart, L. A., & Pinter-Wollman, N. (2007). Large brains and cognition: Where do elephants fit in? Neuroscience and Biobehavioral Reviews, 32, 86–98. Hauser, M. D., Kralik, J., & Botto-Mahan, C. (1999). Problem solving and functional design features: Experiments on cotton-top tamarins, Saguinus oedipus oedipus. Animal Behaviour, 57, 565–582. Hauser, M. D., Santos, L. R., Spaepen, G. M., & Pearson, H. E. (2002). Problem solving, inhibition and domain-specific experience: Experiments on cotton-top tamarins, Saguinus oedipus. Animal Behaviour, 64, 387–396. Hunt, G. R. (2000). Tool use by the New Caledonian Crow Corvus moneduloides to obtain Cerambycidae from Dead Wood. EMU, 100, 109–114. Irie-Sugimoto, N., Kobayashi, T., Sato, T., & Hasegawa, T. (2008). Evidence of means-end behavior in Asian elephants (Elephas maximus). Animal Cognition, 11, 359–365. Irie-Sugimoto, N., Kobayashi, T., Sato, T., & Hasegawa, T. (2009). Relative quantity judgment by Asian elephants (Elephas maximus). Animal Cognition, 12, 193–199. Janic, V. M., & Slater, P. J. B. (1997). Vocal learning mammals. Advances in Study of Behavior, 26, 59–99. Jerison, H. J. (1974). Evolution of the brain and intelligence. New York: Academic Press. McComb, K., Moss, C., Sayialel, S., & Baker, L. (2000). Unusually extensive networks of vocal recognition in African elephants. Animal Behaviour, 59, 1103–1109. Meck, W. H., & Church, R. M. (1983). A mode control model of counting and timing processes. Journal of Experimental Psychology: Animal Behavior Processes, 9, 320–334. Nissani, M. (2006). Do Asian elephants (Elephas maximus) apply causal reasoning to tool-use tasks? Journal of Experimental Psychology: Animal Behavior Processes, 32, 91–96.
181
Payne, K. B., Langbauer W. R., Jr., & Thomas, E. M. (1986). Infrasonic calls of the Asian elephant (Elephas maximus). Behavioral Ecology and Sociobiology, 18, 297–301. Plotnik, J. M., de Waal, F. B. M., & Reiss, D. (2006). Self-recognition in an Asian elephant. Proceedings of the National Academy of Sciences of the United States of America, 103, 17053–17057. Poole, J. H., Tyack, P. L., Stoeger-Horwath, A. S., & Watwood, S. (2005). Animal behaviour: Elephants are capable of vocal learning. Nature, 434, 455–456. Povinelli, D. J., Reaux, J. E., Theali, L. A., & Giambrone, S. (2000). The support problem: Physical connection revisited. In D. J. Povinelli (Ed.), Folk physics for apes: The chimpanzee’s theory of how the world works. New York: Oxford University Press, pp. 254–270. Povinelli, D. J., Rulf, A. B., Landau, K. R., & Bierschwale, D. T. (1993). Self-recognition in chimpanzees (Pan troglodytes): Distribution, ontogeny, and patterns of emergence. Journal of Comparative Psychology, 107, 347–372. Rensch, B. (1957). The intelligence of elephants. Scientific American, 196, 44–49. Rohland, N., Malaspinas, A. S., Pollack, J. L., Slatkin, M., Matheus, P., & Hofreiter, M. (2007). Proboscidean mitogenomics: Chronology and mode of elephant evolution using mastodon as outgroup. PLoS Biology, 5, 1663–1671. Suarez, S. D., & Gallup, G. G. (1981). Self-recognition in chimpanzees and orangutans, but not gorillas. Journal of Human Evolution, 10, 175–188. Sukumar, R. (2001). The living elephants: Evolutionary ecology, behavior, and conservation. New York: Oxford University Press. Vauclair, J. (1996). Animal cognition: An introduction to modern comparative psychology. Cambridge, MA: Harvard University Press. (Received January 28, 2009; accepted May 16, 2009)
© Japanese Psychological Association 2009.
