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CULTURAL SCIENCE JOURNAL 15(1)
DOI: 10.2478/csj-2023-0001
Propagaon of interspecies sexual behaviour
between Japanese macaques and Sika deer: First
evidence
CÉDRIC SUEUR
Université de Strasbourg, France; e-mail: cedric.sueur@iphc.cnrs.fr; 0000-0001-8206-2739
ATSUYUKI OSHIMA
Atsuyuki Ohshima photography, Kyoto, Japan; e-mail: atyk12.info@gmail.com
MARIE PELÉ
Université Catholique de Lille, France; e-mail: marie.pele@univ-catholille.fr 0000-0003-2297-5522
Keywords: tradion, culture, reproducve interference, primate, cervid behaviour
Abstract: This naturalisc note presents a series of observaon of interspecies sexual behaviour
involving Japanese macaques (Macaca fuscata yakui) and Sika deer (Cervus Nippon yakushimae)
on Yakushima Island, Japan. The inial observaon in 2015 revealed a male macaque’s aempt
to engage in sexual acvity with female deer, displaying mate-guarding behaviour. Subsequent
observaons in 2020, 2021 and 2023 showed the connuaon of this behaviour and potenally
the propagaon to other macaques. We categorised this rare behaviour as a case of reproducve
interference and explored hypotheses regarding its funconality. While some suggest nutrional
benefits for the deer, others propose learning, incomplete species recognion, or mate
deprivaon hypotheses. This behaviour may also be selecvely neutral, offering no direct fitness
benefits, but rather represents a behavioural by-product of other interacons between these
two species, which may themselves be adapve. Furthermore, we hypothesise that the observed
propagaon may underlie social transmission and highlight the potenal cognive capacies of
Japanese macaques involving social learning mechanisms and the willingness to adopt non-
insnctual behaviours.
CULTURAL SCIENCE JOURNAL 15 (2023)
Cédric Sueur, Atsuyuki Ohshima, Marie Pelé
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Introducon
Animal culture refers to behaviours, pracces, and tradions that are learned socially within a species
and passed down through generaons. These behaviours, which are not inherited genecally but
through social learning, challenge the belief that culture is unique to humans and offers insights into
animal behaviour, evoluon, and conservaon (Whiten 2000; Laland and Janik 2006; Whiten and
Schaik 2007; Duboscq et al. 2016). Animals, like humans, develop and transmit cultural traits, with
different populaons exhibing disnct behaviours. For example, some chimpanzees use scks to
fish for termites, while others use stones to crack nuts, illustrang the variaon in cultural behaviours
between populaons (Whiten et al. 1999, 2005, 2007; Biro et al. 2006; Matsuzawa 2017). The
concept of animal culture originated in primatology, parcularly through Kinji Imanishi’s study of
Japanese macaques in the mid-20th century. Imanishi’s team observed the spread of potato-washing
behaviour among macaques, providing the first documented example of cultural transmission in
animals (Kawai 1965; Matsuzawa 2015). Jane Goodall’s work with chimpanzees (Pan troglodytes) in
the 1960s further solidified the idea of animal culture, parcularly through her discovery of tool use,
which was learned and transmied socially within groups (Goodall 1986; Whiten et al. 1999). Since
then, animal culture has been observed across various species. Humpback whales (Megaptera
novaeangliae), for instance, exhibit cultural transmission through their songs (Garland et al. 2011),
while New Caledonian crows (Corvus moneduloides) demonstrate cultural tool use (Rutz et al. 2018).
Even species like fruit flies (Drospophila sp.) display cultural tradions in mate choice (Baes et al.
2015). These findings highlight the importance of cultural diversity in animal conservaon,
emphasising that preserving cultural knowledge is as vital as protecng genec diversity (Carvalho
et al. 2022; Sueur 2022).
JAPANESE MACAQUES AND SIKA DEER CULTURES
Direct interacons between Japanese macaques and Sika deer provide a compelling example of the
evoluon of interspecies relaonships. Inially, these species coexisted closely in terms of spaal
proximity, with both benefing from this arrangement. For instance, macaques, while feeding in
trees, oen drop food, which becomes an addional energy source for the deer, enhancing their
foraging efficiency through gleaning (Tsuji et al. 2007). This interacon fosters a strong cohabitaon
dynamic between the two species. A parcularly unusual aspect of this relaonship is the deer’s
coprophagia, where deer consume the feces of macaques, especially around the laer’s sleeping
sites (Nishikawa and Mochida 2010). As their relaonship change, some macaques have been
observed grooming deer, a behaviour that suggests a deepening bond between the species. On
Yakushima Island, this interacon has advanced into a co-culture (Co-culture is the mutual evoluon
of shared behaviours between different species that influence each other through direct or indirect
interacons in a shared environment) (Sueur and Huffman 2024), with macaques even riding on the
backs of Sika deer (Pelé et al. 2017). Similar behaviours have been observed between rhesus
macaques (Macaca mulaa) and sambar deer (Rusa unicolor), suggesng that such complex
interspecies interacons may arise in other environments and among different species (Prasad et al.
2013). Interesngly, these interacons have even led to interspecies sexual behaviours, as observed
in both Yakushima and the Minoh Prefecture in Japan. Male macaques have been documented
engaging in sexual acvity with female Sika deer, and conversely, female macaques with male deer
(Gunst et al. 2018). These instances illustrate the capacity for highly complex and unexpected
behaviours to emerge between species living in close proximity. The evoluon of their interacons –
CULTURAL SCIENCE JOURNAL 15 (2023)
Cédric Sueur, Atsuyuki Ohshima, Marie Pelé
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ranging from shared foraging and grooming to more intricate behaviours like riding and interspecies
sexual acvies – demonstrates significant social and behavioural adaptaon between these two
disnct species. These behaviours are categorised as ‘highly complex’ due to the acve feedback
loops between the species, which foster reciprocal adaptaons, and the layered nature of their
interacons – from foraging and grooming to intricate behaviours like riding and interspecies sexual
acvies – indicang cognive processes, social transmission, and behavioural innovaon that
evolve through mutual influence. They appear to learn from one another and have developed co-
cultural behaviours (Sueur and Huffman 2024).
BEHAVIOURAL ANALYSIS
Original study
During his presence on Yakushima Island, Japan, from October 10 to November 6, 2015, the
photographer Alexandre Bonnefoy observed for the first me the intriguing behaviour of an adult
male Japanese macaque (figure 1a, Video 1). A meline and a map are present in figure 2. This male,
seemingly a peripheral member or part of a group of peripheral males (Sprague 1991), exhibited a
case of heterospecific sexual behaviour, characterised by the mounter performing pelvic thrusng
(i.e. rhythmic movements of the mounter’s pelvic girdle toward the mountee’s back or hindquarter).
While this behaviour was documented for the first me in our study (Pelé et al. 2017), it does not
mean that it did not exist before our observaon. Nonetheless, our colleagues on the site had never
reported witnessing this sexual behaviour unl we shared our video findings with them. The male
lived among other males and did not appear to be part of a mul-male, mul-female group. On
November 6, the macaque male engaged in sexual acvity with at least two female Sika deer.
Notably, the macaque did not display aggression toward the deer but acvely chased away other
peripheral macaque males that approached the ‘guarded’ deer. Its inial interacon with one female
deer involved mounng and displaying sexual behaviours with pelvic thrusng, although penetraon
did not occur. These behaviours occurred at consistent intervals between the same macaque male
and the same deer female, with about ten mounts taking place approximately every 4–5 minutes
over the course of an hour of observaon before the animals disappeared into the forest. The male
subsequently aempted to mount another female deer, which rejected the sexual advances. She
tried to evade the macaque through movements, accelerang her pace, turning around, and
exhibing threatening gestures. Interesngly, shortly aer, a 2018 study revealed that five female
macaques exhibited similar mounng behaviour toward male deer in the Meiji Memorial Forest of
Minoh Quasi-Naonal Park, Minoh Prefecture, near Osaka, Japan – over 600 kilometres away from
Yakushima (Gunst et al. 2018).
In October 2017, we (Marie Pelé and Cédric Sueur) came back for a week to Yakushima to assess
whether the male macaque connued to display this behaviour and whether social transmission was
observed, but we only saw the male macaque close to a deer without sexual behaviour. During this
week we observed from 9 a.m. to 5 p.m. macaques ad libitum, going from group to group on the side
of the unique road along the naonal park, idenfying from three to nine groups per day. We cannot
provide detailed descripons of each group since we were unable to idenfy them specifically. Out
of the numerous groups in Yakushima, only three are closely monitored. Our knowledge is limited to
certain individual idenficaon and insights into the home range and group size of macaques, with
observaons of up to nine groups per day. The density of macaques in Yakushima is exceponally
high. Within the lowland coastal zone, ranging from 0 to 300 metres above sea level, it is esmated
that there were about 4.8 troops and between 62.4 to 99.8 monkeys per square kilometre. To
CULTURAL SCIENCE JOURNAL 15 (2023)
Cédric Sueur, Atsuyuki Ohshima, Marie Pelé
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enhance the reliability of our observaons based on video evidence provided by local inhabitants
and researchers, we have corroborated these recordings with extensive local knowledge of the area’s
wildlife and the consistent behaviour paerns of the subjects over me. This approach has allowed
us to migate some of the limitaons associated with the opportunisc nature of data collecon.
Cues indicang a propagaon
In 2020 and 2021, new videos were recorded by an inhabitant of Yakushima (Cameron Riki Joyce)
documenng interspecies sexual behaviour. No informaon had been disclosed about his daily visits
to the park, including key details such as the locaon and duraon of the observaons. On August
23, 2020, a male macaque looking like the one previously observed in 2015 and 2017 was seen riding
a female deer and engaging in sexual behaviour for nine seconds (figure 1b, Video 2). This male was
idenfied by his disnct almond-shaped eyes, though we cannot be certain, with 100% accuracy,
that he was the same individual. However, this does not affect the overall aim and conclusions of this
note. In the video, the male was not seen with any other macaques. However, on March 12, 2021,
the male was observed surrounded by other macaques, including one male, at least six females and
three juveniles (Video 3). On the same day, a young female climbed onto a male deer, quickly
groomed it, and then engaged in two sequences of sexual behaviours (with pelvic thrusng as
behavioural units lasng five and seven seconds, respecvely), followed by an extended period of
grooming the deer (figure 1c, video 3). We defined a sequence of sexual behaviour as at least three
consecuve pelvic thrusng behaviour. Later, another female, older than the first one described
(differenated through the body size and corpulence), also briefly engaged in a sequence of sexual
behaviour with a male deer before being ejected by the deer (figure 1d, video 4). On November 29,
2023, a female exhibited mounting behaviour with pelvic thrusting on a male deer. Video 5,
provided by A. Otsuyuki Ohshima, showcases activities within the national park during the week
of November 27, capturing moments from dawn until dusk. Observations were made ad
libitum, moving between groups along the roadside.
The sexual behaviour displayed by female macaques toward male deer differs from the typical
mang behaviours observed with male macaques, as the pelvic movements are slower, less rhythmic,
and lack the thrusng intensity usually seen in heterosexual interacons. Instead, these movements
resemble the slower pelvic moons oen observed in female-female homosexual interacons
among macaques. These observaons indicate two significant findings: firstly, if it indeed is the
original male observed in 2015, the macaque exhibited a connuaon of the original behaviour, and
secondly, these observaons suggest possible propagaon (Duboscq et al. 2016) of this behaviour to
other group members though further data and evidence are needed to confirm this transmission.
Notably, this propagaon occurred between macaques of different sexes, from one male to, at least,
two females.
The appearance of rare and unique behaviours, such as the interspecies interacons documented
here, highlights the value of non-standard methods like cizen science. As we see in this study, videos
captured by photographers and tour guides provide invaluable insights, serving as powerful
complements to rigorous scienfic methods and expanding the scope of discovery beyond standard
observaonal approaches alone (Silvertown2009; Nelson and Fijn 2013; Sueur et al. 2020; Fraisl et
al. 2022).
CULTURAL SCIENCE JOURNAL 15 (2023)
Cédric Sueur, Atsuyuki Ohshima, Marie Pelé
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Figure 1. Cases of heterospecific sexual behaviour between Japanese macaques and Sika deer. a. First
observaon made in 2015, a male macaque on a female deer. b. Second observaon of probably the
same male macaque on a female deer made in 2020. c. and d. Observaon of female macaques on male
deer indicang a social transmission.
Figure 2: meline and maps of events. 2015: The first observaon of interspecies sexual behaviour
between a male Japanese macaque and a female Sika deer on Yakushima Island was documented. The
male macaque displayed mang behaviours toward the deer without aggression, guarding the deer
against other male macaques. 2017: Cédric Sueur and Marie Pelé returned to Yakushima for a week to
assess whether the male macaque connued this behaviour and to observe potenal social
transmission. However, no further sexual behaviour was observed during this visit. 2018: Observaons
in the Meiji Memorial Forest of Minoh Quasi-Naonal Park near Osaka (over 600 km from Yakushima)
documented five female Japanese macaques displaying similar mounng behaviour toward male deer,
indicang a spread of this behaviour to other regions and individuals. 2020: A video recorded by a
Yakushima resident (Cameron Riki Joyce) captured a male macaque engaging in sexual behaviour with
a female deer for nine seconds. The male macaque was idenfied by unique physical features but could
CULTURAL SCIENCE JOURNAL 15 (2023)
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not be definively confirmed as the same individual observed in 2015 and 2017. 2021: Another video
captured a young female macaque climbing onto a male deer, engaging in grooming and short
sequences of mang-like behaviours, followed by grooming. Later, an older female macaque also briefly
displayed similar behaviour with a male deer, suggesng possible social transmission. 2023: On
November 29, a female macaque was observed displaying mounng behaviour with pelvic thrusng on
a male deer. This observaon further supported the possibility of social transmission, as behaviours
now involved both male and female macaques.
FUNCTIONAL ANALYSIS AND HYPOTHESES
This rare instance of heterospecific sexual interacon aempt is categorised as one of the seven
cases of reproducve interference as defined by Gröning and Hochkirch (2008). They define
reproducve interference as any interspecific interacon occurring during mate acquision that
detrimentally impacts the fitness of at least one species involved, resulng from incomplete species
recognion. They categorise reproducve interference into seven disnct types: signal jamming,
heterospecific rivalry, misdirected courtship, heterospecific mang aempts, erroneous female
choice, heterospecific mang, and hybridisaon. However, the likelihood that Japanese macaques
misrecognise sika deer as conspecific is minimal. This improbability is underscored by the long-term
coexistence and frequent interacons these two species share on Yakushima Island. Instead, the
observed interspecies interacons, including sexual behaviours, likely emerge from the close
proximity and the complex, reciprocal interspecies dynamics that have developed, rather than from
errors in species recognion.
The first observaon and second observaons involve sexual interacon between a male
Japanese macaque and a female Sika deer, although there was no penetraon. In the other
observaons, it involves female macaques and male deer. Unlike some cases of interspecific
interacons that involve sexual harassment or coercion (Cluon-Brock and Parker 1995), these
behaviours appeared different; the deer are always in the vicinity of macaques looking for food le
by the macaques or eang the feces of the monkeys (Tsuji et al. 2007; Nishikawa and Mochida 2010;
Pelé et al. 2017). The female deer’s behaviour, specifically licking the macaque’s seminal fluid,
suggests that it might see this behaviour as a source of nutrion. However, this hypothesis cannot
explain why the male deer let females climb on them. We first suggested that the hormonal surge
during the macaque breeding season, coupled with their kind-of cooperave interacons as
grooming exchange and play with Sika deer, may have contributed to this heterospecific sexual
behaviour. In our 2017 paper (Pelé et al. 2017), we proposed alternave explanaons for this
behaviour. One theory suggested it might serve as a learning mechanism for copulaon. Another
considered the possibility of incomplete species recognion which is quite improbable. Addionally,
we introduced the ‘mate deprivaon hypothesis’, which posits that males with limited access to
females might be more inclined to engage in such behaviour. This hypothesis is parcularly relevant
in species facing intense sexual compeon. Similar paerns have been observed in other sexual
behaviours among Japanese macaques, such as masturbaon (Thomsen and Sols 2004) and
homosexual behaviour (Leca et al. 2015).
However, these new observaons do not confirm these hypotheses. The male connued
displaying interspecies sexual behaviour despite appearing to be dominant within his group, as
shown in the video where he is seen chasing and threatening other group members. This behaviour
may also be selecvely neutral, offering no direct fitness benefits, but rather represents a behavioural
by-product of other interacons between these two species, which may themselves be adapve.
CULTURAL SCIENCE JOURNAL 15 (2023)
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COGNITIVE ANALYSIS AND HYPOTHESES
Regarding the interspecies sexual behaviour
Sexual behaviours observed among species can be aributed to their close proximity and frequent
interacons. Indeed, complex interspecific interacons have been observed in various species,
ranging from mixed-species groups to mutual exchanges of services between different species. These
interacons have been documented in different contexts and can have various benefits (Axelrod and
Hamilton 1981). For example, mixed-species groups can benefit from proximity to members of other
species, leading to indirect advantages such as increased vigilance against predators or access to
dropped fruits from trees (Tsuji et al. 2007; Nishikawa and Mochida 2010). In the case of Japanese
macaques and Sika deer on Yakushima Island, direct interacons occur and may have conducted to
these remarkable sexual behaviours between the two species. Indeed, the macaques drop food from
trees, which serves as an energy source for the deer, enhancing their foraging efficiency. This results
in a close cohabitaon between the two species. Addionally, the deer engage in coprophagia by
consuming the feces of Japanese macaques, parcularly around macaque sleeping sites. Some
macaques have even been observed grooming the deer and aempng to ride them without sexual
behaviour involved. Similar interacons have been reported between rhesus macaques and sambar
deer in India (Prasad et al. 2013). The sexual behaviour may have emerged from the close proximity
and exisng rodeo-like behaviours at a parcular moment.
Regarding the potenal social transmission
The observaon of interspecies sexual behaviour between Japanese macaques and Sika deer has
revealed complex interacons that point to both cognive capabilies and the potenal for social
transmission of behaviours. The objecve here is to clarify the differences between the cognive
processes implied by these behaviours and the hypothesis regarding social transmission (Whiten
2000; Hoppi and Laland 2013; Duboscq et al. 2016). Regarding cognive capacies and behavioural
innovaon, the inial sighngs in 2015 suggested a novel aspect of macaque behaviour, although it
is unlikely to be the first occurrence of this innovaon given the absence of systemac, long-term
data collecon and similar behaviours observed in other populaons. However, this was the first
documented instance, as other colleagues regularly present in the field had never previously
observed it. These innovaons illustrate the macaques' ability to adapt and innovate by exploring
mang opportunies outside their species, an indicator of behavioural flexibility and curiosity
(Vancatova 2008; Aplin et al. 2015). Addionally, the guarding behaviour observed may reflect a level
of understanding in managing compeon for mates. This guarding may serve not only as a
reproducve strategy but also as a way to protect the deer as a social or play-related resource rather
than as a direct mang partner (Vasey 2004; Gunst et al. 2018). The different responses observed in
female macaques engaging in reproducve interference with male deer also raise intriguing
quesons about their ability to discern between potenal mang partners. This behaviour implies
that some level of cognive processing may be influencing their decision-making processes in these
interacons (De Petrillo and Rosa 2021).
The social transmission hypothesis is supported by observaons from 2020 to 2023, during which
macaques of both sexes exhibited similar interspecies interacons. These findings may align with the
hypothesis that social learning and transmission are at play, as the spread of this behaviour across
different individuals, potenally from males to females, suggests an advanced form of social learning.
CULTURAL SCIENCE JOURNAL 15 (2023)
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This behaviour indicates that macaques may be open to adopng behaviours culturally transmied
in this species (Zhang and Watanabe 2007, Zhang et al. 2007, Huffman et al. 2010).
We recognise the limitaons posed by the opportunisc nature of our observaons, including the
potenal for previous unrecorded instances of this behaviour among females before 2015. The
absence of long-term, connuous observaon precludes definive conclusions about the origins and
spread of this behaviour among macaques. Despite these limitaons, our interpretaon of the data
is suggesve evidence of behaviour in mulple individuals within the same social group, a paern
that aligns with documented instances of social learning in non-human primates. While we cannot
definively rule out individual learning or independent innovaon as explanaons for the observed
behaviour, the simultaneous occurrence in closely associated individuals suggests a social
component to the behaviour’s acquision. Our suggeson of social transmission is also informed by
comparave analysis with documented cases of social learning in primates, where behaviours spread
through observaon and imitaon within social groups. We also acknowledge the possibility of
alternave explanaons for the observed behaviour, including individual learning or a shared
environmental influence as some studies have not found any evidence of observaonal learning or
imitaon in primates (Nagell et al. 1993, Tomasello and Call 1994, Call et al 2005, Tennie et al 2006,
Clay and Tennie 2018, Neadle et al. 2021).
To fully understand the learning mechanisms underlying this behaviour, addional data would be
required on several fronts, as noted by reviewers. First, establishing the ming of behaviour
innovaon and duraon within the group is crical; although we noted the first recorded
occurrence in 2015, this likely does not reflect the initial appearance of deer mounting. Second,
without continuous monitoring, it remains unclear if other individuals practised this behaviour
prior to the second observation, when females were noted engaging in deer mounting. We,
therefore, lack data on the original innovator of the behaviour and the potential pathways of
social transmission within the group, if any. It is equally possible that all members began
engaging in this behaviour independently, with no social learning involved. To rigorously assess
the role of learning, controlled experimental data would be essential, ideally involving naïve
individuals exposed to social stimuli in a controlled setting. These experiments would require
testing individuals confirmed to be naïve to deer mounting and systematically introducing the
behaviour to discern the mechanisms behind its emergence. Given that this behaviour has also
been observed in a separate group of macaques (Gunst et al. 2018), a simpler assumption may
be that complex social learning mechanisms are not required for this behaviour to manifest;
rather, exposure to the stimulus – in this case, the deer – may be suicient for its appearance.
EVOLUTIONARY CONSIDERATIONS
Interspecific interacons in animals can have both negave and posive outcomes. Negave
interacons are exemplified by prey-predator relaonships (Freedman and Waltman 1984), where
one species benefits at the expense of the other. Posive interacons are seen in mutualism (Axelrod
and Hamilton 1981), where both species benefit. Heterospecific sexual behaviour, which involves
sexual interacons between individuals of different species, has been mainly described in closely
related species and has been studied in terms of its effects on fitness, hybridisaon, and species
survival (Burdfield-Steel 2012; Kyogoku 2015; Shuker et al. 2015). There have been few documented
cases of heterospecific mang between individuals of distantly related species, and these instances
have primarily occurred in capve or human-animal interacon sengs (Beetz 2004; Gröning and
Hochkirch 2008; Beirne 2009). One study reports sexual harassment of king penguins by Antarcc
CULTURAL SCIENCE JOURNAL 15 (2023)
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9
fur seals, where some penguins were killed and eaten at the end of their mang behaviour (de Bruyn
et al. 2008; Haddad et al. 2015). This note underscores the relave scarcity of research on
interspecies sexual behaviour, parcularly among distant species in natural sengs. It also highlights
the potenal consequences and complexies associated with such interacons, which can range
from fitness implicaons to survival challenges, depending on the circumstances and species
involved (Sueur and Huffman 2024). The rarity of heterospecific sexual interacons between distant
species makes our observaons significant, providing insights into the evoluon of interspecific
mang behaviour in the animal kingdom and its potenal relevance to understand zoophilia in
humans (Beetz 2004; Beirne 2009).
This interspecies sexual behaviour, if it is socially transmied, which seems probable given past
cultural behaviours observed in macaques, may represent a form of cultural transmission among the
macaques. This cultural transmission can have profound implicaons for the evoluonary trajectory
of a group (van Schaik et al. 2012; Maei 2014; Henrich 2017). It may allow for the spread of novel
behaviours that provide adapve advantages. Cultural behaviours are well documented in Japanese
macaques (Bonnefoy et al. 2016), with some serving praccal funcons, such as the use of hot
springs for bathing (Zhang et al. 2007), washing potatoes (Matsuzawa 2015), or forming strong
aggregaons known as ‘saru-dango.’ However, the funconality of certain other behaviours, such as
the stone-handling behaviour (Leca et al. 2007; Huffman et al. 2010) or these heterospecific sexual
interacons, remains a topic of ongoing debate. These behaviours, nonetheless, illuminate the
intricate social and cultural lives of Japanese macaques. As researchers, it is imperave that we delve
deeper into our observaons and analyses of these behaviours.
CONCLUSION
In conclusion, this note on interspecies interacons between Japanese macaques and Sika deer on
Yakushima Island reveals a complex dynamic that extends beyond mere coexistence. The
documented instances of macaques engaging in heterospecific behaviours with deer, including
grooming, riding, and sexual behaviours, suggest significant cognive and social dimensions. These
interacons highlight the adaptability and behavioural innovaon within macaque populaons,
which may stem from close proximity and regular interspecies encounters. The possibility of social
transmission of these behaviours among macaques implies that such interacons could become
culturally embedded within specific groups, similar to previously documented cultural behaviours.
While heterospecific sexual behaviour is rare and has largely been observed in closely related
species, its occurrence here offers insights into the cognive and social flexibility of macaques.
However, these findings remain preliminary due to the opportunisc nature of observaons. Further
research is needed to determine the mechanisms underlying these behaviours, their evoluonary
implicaons, and the potenal for social learning among individuals. This note adds a unique
dimension to our understanding of animal culture and cross-species interacons, urging a deeper
exploraon of how such behaviours evolve and persist in animal sociees.
Acknowledgements
Funding: This research was funded by an internaonal research project (IRP Comp²A) between the
CNRS and Kyoto University.
CULTURAL SCIENCE JOURNAL 15 (2023)
Cédric Sueur, Atsuyuki Ohshima, Marie Pelé
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Acknowledgments: We thank the Kagoshima Prefecture for the authorisaon of presence in the
Yakushima Naonal Park. We thank Hideki Sugiura for his help on this research. We thank Alexandre
Bonnefoy (Edions Issekinicho) and Cameron Riki Joyce (Yakushima Experience) for their courtesy to
use their pictures and videos.
Conflicts of interest/Compeng interests: The authors are not aware of any conflicts of interest that
may have influenced the material presented in this arcle.
Availability of material:
Video 1: hps://youtu.be/l8HFDnM7Sdw?si=qdaFyeCqfRTRh9pP;
Video 2: hps://youtube.com/shorts/wfDasKQiCb0?si=85BG8v5F7PxvMbmK ;
Video 3: hps://youtube.com/shorts/qK1SEW106D8?si=aNxzkhZ_uXIdIhBH ;
Video 4: hps://youtu.be/peYCBIa0fpk?si=L_5M_BoEzRTborHw ;
Video 5: hps://youtu.be/Df0lw_tBRu8
Authors’ contribuons: Data curaon: AO, CS & MP. Visualisaon: CS & MP. Original dra: CS. Wring,
review and eding: AO, CS & MP.
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Author informaon
Cédric Sueur is Full Professor at the University of Strasbourg. He is mainly working on animal
behaviour and specifically on social networking, culture and decision-making in animal groups
at the Institut Pluridisciplinaire Hubert Curien. He is also member of the Institut Universitaire
de France (http://www.iufrance.fr).
Atsuyuki Oshima is a professional wildlife and nature photographer based in Kyoto, Japan.
Renowned for capturing the essence of wildlife, particularly monkeys, his stunning work
showcases nature's beauty. He was awarded Wildlife Photographer of the Year in 2023.
Marie Pelé is a researcher at the Anthropo-Lab, ETHICS Laboratory of the Catholic University of
Lille, specializing in animal and human ethology. Her work focuses on animal cognition and
human-animal relationships, exploring societal perspectives on the management of individuals
and species conservation. By integrating human disciplines such as ethics, sociology, and
psychology with animal-centered fields like ethology, ecology, and biology, she develops an
approach known as "ethological engineering," which combines observation and
experimentation to foster a sustainable human-animal relationship.
