Macaques are among the
most widespread monkeys among primates and have 19 existing species and numerous
others in the fossil record (Hoelzer, & Melnick, 1996). Japanese Macaques (Macaca fuscata)
are called “Nihon zaru” in Japanese, meaning “Japanese Monkey.” They are one of the most successful
macaques, and live in the highest latitude (41º 31’N)
(Masui, 1988) among all primates. This paper is a
descriptive paper profiling the unique morphological, geographical, dietary,
reproductive, developmental, social and behavioral characteristic of Japanese
macaques.
Japanese macaques (later
to be abbreviated JM) are medium sized and have a stocky body with both a head
and body length of approximately 500mm high (20in.) (Napier & Napier,
1985). In Iwatayama Natural Park
(INP), Arashiyama, the biggest male was about 600mm, the biggest female was
about 450mm, and infants were about 300mm (personal observation, 2000). Sexual dimorphism is considerable in
weight, body size and canine size (Napier & Napier, 1985). Tail length is less than a quarter of
the head and body length (Napier & Napier, 1985). JM have grayish or brownish fur color, well-developed cheek paunches,
ischial callosities (Napier & Napier, 1985; personal observation), and red
faces. The total number of teeth
is 32 and there is a fifth cusp on the lower third molar (Napier & Napier,
1985). They also have fully
opposable thumbs (Napier & Napier, 1985; personal observation) and have
excellent precision grip (personal observation).
Locomotion of JM is quadrupedal
(Napier & Napier, 1985). They
are highly terrestrial (Kawai, 1990/1993; Richard, 1985) and move very fast
quadropedally on the ground, especially during the artificial feeding time,
chasing and fighting (personal observation). They also have a unique mode of
bipedal locomotion called “facultative bipedalism.” This locomotion occurs when they hold something with both
hands (Kawai, 1990/1993; Napier & Napier, 1985).
Adaptation to cold temperature
Winter in Japan is very
cold, and from 1961-90 the temperature reached an average of –2.5º Celsius in
the northern part of Honshu island (Statistics Bureau & Statistics Center
Japan, 2001). Accordingly, JM grow
heavy insulating coats during winter to maintain their body temperature during
cold temperatures (Tokura et al. 1975 as cited in Richard, 1985). They also have a behavioral mechanism
to prevent a decrease in body temperature. JM spend much time sunbathing on slopes facing south and
sleep in deciduous trees on which snow does not accumulate much (Richard,
1985).
Masui (1988) reported
macaques in four habitats. The
first group is the macaques of the northern limit (Shimokita Peninsula
troops). The Shimokita
Peninsula is located at the northern part of the Honshu island and the northwest
area of this peninsula (41º 31’N) is the northern limit of JM habitat (Masui,
1988; Nakagawa, Iwamoto, Yokota, & Soumah, 1996). The temperature can reach –15º Celsius in this region and
deciduous trees and conifers are the dominant vegetation. Three troops (troop I [40 individuals],
troop M [36], and troop Z [40-50], total 116-126 individuals) are recorded in
this region by Masui (1988). JM cannot
live any further north than this region, thus there are no JM in Hokkaido
island (Masui, 1988), which is located northern from the top of Honshu
island. The second group is the
snow-mountain macaques (e.g. Hakusan Jyadani troops). In Hakusan Jyadani, two troops (troop “Kamuri A” [46
individuals], and troop “Taiko B” [12], total 58 individuals) were observed by
Masui (1988). The third one is the
seaside macaques (e.g. Okushima sea side, Tubonega Cho troop). In Tubonega Cho, Masui (1988) recorded
a troop of 44-60 individuals. The
final group is the macaque of the southern islands (e.g. Yakushima Island
troops). Yakushima island (30º 30’N)
is the southern limit of the habitat of JM, which has wide range of vegetation,
including subtropical and temperate plants and broad-leaved evergreen forests
(Masui, 1988). The population
density of macaques in Yakushima is higher than in the other habitats in Japan
(Takasaki, 1981 as cited in Agetsuma, 1995a). Generally JM can live within the north and south limits, and some
other well-known places are Arashiyama (35º 00’N) (Fedigan & Griffin,
1996), Takasakiyama (33º 07’N), and Koshima (31º 38’N) (Nakagawa et al.,
1996).
16% of JM offspring die
at an age younger than 2 years old, and the most monkeys die younger than 20
years old (Masui et al. 1975 as cited in Richard, 1985). The oldest female macaque recorded in
Fedigan’s (1991) research was 32 years old and the average life expectancy was
25+ in his study. No data was
found on the life expectancy of male JM.
Males reach sexual maturity at 4.5 years old and females at 3.5 years
(Napier & Napier, 1985).
JM are omnivorous because
they eat insects, crabs, and bird eggs, although the majority of their diet
consists of leaves (Kawai, 1990/1993).
In addition to the wide gap between the climates of the northern and
southern regions, Japan also has four seasons and the temperature varies from
season to season widely.
Correspondingly, there are substantial seasonal and regional variations
in diet and foraging strategies.
Seasonal and regional variation in
diet
Nakagawa et al. (1996)
found out that during autumn season, monkeys of both Koshima (southern Japan)
and Kinkazan (northern Japan) met calorie and protein requirements, but their
intake was hardly enough in winter in both regions (Nakagawa et al.,
1996). Nakagawa et al. also found
out that during the autumn Kinkazan monkeys met most of their protein
requirements by eating protein-rich insects, whereas Koshima monkeys did so by
eating protein- rich plants. The
food deficiency is more severe in Kinkazan (northern) than in Koshima (southern)
because Kinkazan region is covered with lots of snow during the winter
(Nakagawa et al., 1996). During
the winter the main food of Koshima monkeys is the evergreen-broad leaves,
whereas bark, winter buds, and twigs are Kinkazan monkey’s main food source
(Nakagawa et al., 1996). In Honshu
island (where Kinkazan is located, Koshima is in Kyusyu island located below
Honshu island), JM eat bark through snowy winters (from January to March) when
leaves are not available (Agetsuma, 1995a; Napier & Napier, 1985). Richard reported five distinct patterns
of winterfeeding behavior depending on the amount of the snow covering the
grounds; green-leaf eating, remnants eating, carex eating, sasa eating, and
bark eating (See Suzuki, 1965 as cited in Richard, 1985).
The diet of Yakushima
(Southern Japan) macaques is remarkably diverse and consists of 84 species (151
items) of plants, fruits, seeds, 58 species of nuts, 14 species of flowers,
leaves, shoots, buds of 45 species of woody plants and an additional 3 species
of grasses and herbs, 4 species of ferns, and many unknown species of fungi,
several species of insects, and vertebrates (Agetsuma, 1995a). Agetsuma’s (1995a) research showed
seasonal variation of diets in Yakushima.
Insects are more often eaten during August, fallen seeds during January,
mature and young leaves during April, fruits during November, seeds during
September, and flowers during March.
He attributed these results to both the availability of the food source
and the temperature. Their feeding
on seeds, flowers, young leaves, was more likely to be affected by the
availability, whereas feeding on fallen seeds, mature leaves, and fruits was
affected by temperature (Agetsuma, 1995a).
Other studies reported that most of the seaside monkeys’
diet consists of a bayberry, however, they come down to the seashore during the
winter to catch shellfish (Masui, 1988).
Hazama
(1968) also recorded 192 different species of plants eaten by JM in Arashiyama
within their home range during three-years (as cited in Huffman, 1991a).
Seasonal and regional variation in
foraging strategies
Agetsuma (1995b) found
out Yakushima JM spent more time searching for high energy foods (such as
fruit, seeds, insects, and fungi) than low energy foods (such as fallen seeds,
leaves, young leaves, and flowers) because they might be aware that although
high energy foods are difficult to find they give more energy. In contrast to the searching time,
Yakushima JM spend less time eating high energy foods than low energy foods,
because it takes more time to digest fiber rich, low energy leaves than to
digest the fruit which contains more energy. Agetsuma (1995a & 1995b) also found out that monkeys of
Yakushima island move more in summer, when high energy foods are more
available, than in winter. On the other
hand, they spend more time feeding during winter because only low energy food
is available.
Reproductive characteristics
Female mate choice behavior
Mate choice behavior of
female JM is well reported. Mate
choice behavior is defined as “any behavioural pattern shown by members of one
sex that increases the probability of fertile matings with particular members
of the opposite sex” (Halliday, 1983 as cited in Soltis et al., 1997a). Although male dominance rank is
sometimes a significant predictor of mating and reproductive outcome, female
mate choice behavior might intervene in the outcome (Huffman, 1991b; Soltis et
al., 1997b).
Soltis et al. (1997a)
proposed a model of female mate choice.
They suggested that “in the female mate-choice model, females choose
mates by differential proximity maintainace, and male aggression increases as a
function of increased time in proximity” (Soltis et al., 1997a). Their study supported this model; as
female proximity maintenance increased, male aggression toward the females also
increased, which in effect increased the rate of fertile matings (Soltis et
al., 1997a). They concluded that
females actively chose their mate by maintaining proximity to preferred males
and avoided others. The male aggression
during the breeding season seemed to be the result of the increased time spend
in proximity and not to be a mode of sexual coercion (Soltis et al.,
1997a). Soltis et al. (1997b) also
showed that the high male attractivity is more likely to result in mating and
reproductive success. In his
study, a high rank male winning a male-male competition over a female did not necessarily
lead to mating success, rather the female mate choice surpassed the male sexual
solicitation (Soltis et al., 1997b).
The attractiveness ranking of a male predicted his success in mating and
reproduction more accurately than his dominance ranking.
Huffman’s (1991b) study
also suggested that female JM actively initiated and maintained consortship
with males for more than a day and rejected other male’s solicitation during
that time. Huffman (1991b) also
recorded that mate choice of female JM was affected by the presence or lack of
past sexual relationship with potential males, rather than the immediate
results of solicitation itself.
There was also a tendency among females to prefer sexually unfamiliar
males during estrus (Huffman, 1991b).
Thus, male sexual solicitation plays only a proximate role rather than an
ultimate influence on the female’s mate choice.
Birth
JM females have seasonality in their reproduction
cycles (Tokuda, 1961-2; Kawai, Azuma & Yoshida, 1967; Nigi, 1976; Eaton et
al., 1987; Gouzoules, Gouzoules &Fedigan, 1981 as cited in Fedigan &
Griffin, 1996). Fedigan’s (1991)
study showed that the reproductive peak of female JM is during the second
trimester (10-19 yeas old).
Fedigan and Griffin (1996) recorded the highest rate of birth among
monkeys in Arashiyama was during late May and JM have a constant and
group-specific circannual pattern of seasonal reproduction for many years.
Interesting behavioral
characteristics of a new mother on the day of birth are worth noting. In Thomsen’s & Soltis’ study
(2000), the time spent in grooming, moving, foraging, and feeding by new
mothers decreased on the day of birth, and they spent more time resting. Thomsen and Soltis also observed less
social contact with males, rejection of grooming, and less aggression received
from males towards the mother on the day of birth. Their diet also changed from mature and new leaves and
shoots during prepartum period to fruit during postpartum period (Thomsen &
Soltis, 2000). I speculate this is
probably because a new mother needs a more immediate source of energy from
fruits, which are rich is nutrition and easy to digest. In JM, the mother eats the placenta
right after the birth (Kawai, 1990/1993).
Other reproductive features reported include the presence of incest taboo
within third degree relatives (Kawai, 1990/1993) and their gestation period of
approximately 165 days (Napier & Napier, 1985).
Mother-infant relationship
The mother-infant bond is
strong in JM and starts forming at the licking behavior at the time of birth
(Kawai, 1990/1993). Kawai
(1990/1993) documented that when their offspring died of some cause, mothers
carried the corpses around. This “carrying
behavior” is limited to a certain period of time. For example, they do not carry around offspring more than
3months old (after the lactation period), and miscarried babies and stillborn
children are also not carried.
Only a baby who dies during lactation period is carried, which indicates
that the lactation creates a strong mother-infant bond. The mother-infant bond is so strong
that most of JM do not forget about their mothers forever (Kawai,
1990/1993). Female macaques learn
to raise children. When a female
macaque was separated from her mother right after the birth and raised alone,
she did not know how to nurse her newborn properly when she gave birth, and her
baby died (Kawai, 1990/1993).
Child development
JM babies begin to toddle
after 20 days (Kawai, 1990/1993).
After one month, a baby will start climbing and will begin to be carried
on its mother’s back rather than clinging to the mother’s abdomen. At the beginning, it is difficult for
an infant to balance on its mother’s back, but gradually, a baby learns to
balance with its mothers help (Kawai, 1990/1993). Kawai (1990/1993) also found that JM have a “rebellious age”,
(difficult time as seen in human teenagers) after 3-4 months. During this period, infants start to
have dilemmas between dependence and independence on their mother. Infants tried to balance on their
mother’s back but when they failed, infants started to exaggerate crying and
refused to practice. Then, the
mother would approach and start to push baby onto the ground or give a little
bite to discipline the baby.
Social characteristics
The average group size of
JM is 5-70 individuals (Masui, 1988) and they form multi-male groups with a
strict dominance hierarchy in males and females (Masui, 1988; Napier &
Napier, 1985; Soltis et al., 1997b).
A troop usually has a single male “boss” (Masui, 1988; Sprague, Suzuki,
& Tsukahara, 1996). The
dominance chart of a troop in INP, Arashiyama, is very precise and detailed. Virtually all members of the troop are
listed according with their dominance level (personal observation).
Fedigan (1976) developed
twelve role typologies among the same monkeys of Arashiyama that I
observed. Those roles are 1 Adult
central males: always found in the core of the troop, 2 Adult peripheral males:
often found away from the troop, 3 Adult nucleus female: always found in the
core of the troop, 4 Adult central females: not only found in the core of the
troop, but rather they are the core of the troop, 5 Adult floating females:
found away from the main body of the troop, 6 Subadult peripheral males: found
away from the body of the troop more often than any other group, 7 Subadult
central females: always found in the core of the troop, 8 Subadult floating
females: often found away from the main body of the troop, 9 Juvenile central
males: almost always found in the core, 10 Juvenile floating males: fairly
often found away from the body of the troop, 11 Juvenile central females:
always found in the core of the troop, 12 Juvenile floating females: sometimes
found away from the main body (See Fedigan, 1976 pp. 54-65 for further detail
description of each role).
The male ranking is very
stable among a troop (Sprague, Suzuki, & Tsukahara, 1996) and often
correlated with age (Hanby, Robertson, & Phoenix, 1971; Rowell, 1974;
Drickamer & Vessey 1973; Norikoshi& Koyama 1975 as cited in Huffman,
1991b). Pavelka, Gillespie, &
Griffin (1991) recorded that the highest number of low ranked individuals are
existent among the young males, while the highest number of high ranked individuals
are present among the old males.
Males with a higher rank are also found to be more sociable than lower
ranked males (Pavelka, Gillespie, & Griffin, 1991). Interestingly, consistent correlation
is lacking between dominance rank and reproductive success, thus, high
dominance rank does not necessarily indicate high reproductive success in JM
(Soltis et al., 1997b). Other
factors influencing reproductive success will be discussed later.
Sprague, Suzuki, and
Tsukahara (1996) reported four social mechanisms by which male JM monkeys
obtain the alpha rank based on 37 years of data. The following are adopted from Sprague et al. (1996).
1.
Succession: “a male succeeds to the alpha rank as a result of the death
or departure of the previous alpha male.”
This is common in large and provisioned troops.
2.
Rank turn over: “a change in relative rank results in an alpha male
losing his rank to another male of the same troop, usually the second ranking
male.”
3.
Troop fission: “a male becomes the alpha male of a fission troop, either
by a) shifting over to the new troop from the original group, or b) arriving as
a non-troop male to join a fission group that is not accompanied by any prior
male residents of the original troop.”
4.
Troop take-over: a non-troop male aggressively takes over the alpha rank
of a troop.
Sprague et al. (1996) recorded the
aggressive take-over as the most popular method of attaining alpha rank among
Yakushima monkeys, whereas succession was the most common method among the
other samples (Arashiyama, Takasakiyama, Ryozen troop, Shiga A troop). Thus, they concluded that succession is
the most common social mechanism by which male JM obtain alpha rank.
The primary purpose of
the female ranking system is to facilitate the group coexistence (Takahata,
1991). Takahata (1991) reported that
the dominance relationship among the unrelated females did not change for 10
years, indicating very conservative female dominance relationships. Kinship is important in female dominance,
as the strongest relationship exists between mothers and their female offspring
(Thomsen & Soltis, 2000). The
offspring of a high-ranking mother receives a high rank transmitted by their
mother (Napier & Napier, 1985) through a strategy called dependent
ranking (to be discussed later).
Kawamura (1965) suggested two principles: 1) Daughter’s ranking is right
after her mother’s, & 2) the younger offspring is ranked higher than older
ones (as cited in Takahata, 1991).
The second principle is called “youngest ascendancy.” Takahata’s study (1991) confirmed these
principles reporting that the majority of adult offspring did not confront
their mother, and the older sisters were dominated by the younger ones.
Social rank among infants
sets within a year and a half after the birth (Kawai, 1990/1993) from one of
the following two ways. The first
method is called basic ranking formation and the second one is dependent
ranking formation. The former is formed by one versus one power
relationships, and the latter is formed by one versus one with the help of
others. For example, A is stronger
than B, thus, higher in basic rank, but B can be higher than A with the help of
mother C or brother D; A vs B+C+D.
The rank of infants with a high rank mother tends to be higher because
of this dependent ranking (Kawai, 1990/1993). Playing with others is also an important method by which
their ranking is formed; a winner gets higher rank than a loser (Kawai,
1990/1993). Despite the ranking,
Kawai (1990/1993) also reported evidence of brotherly love between the infants.
The troops on Shimokita
Peninsula have a wider territory (30 square kilometers) than the troops on
Yakushima Island (1 square kilometers) (Masui, 1988). This difference in territory size can give rise to differences
in behavioral skills in each group.
Masui (1988) speculated that the Shimokita monkeys have better visual spatial
abilities because they have to distinguish between wider ranges of
territory. On the other hand,
Yakushima monkeys have better social skills because of a smaller amount of
space per individual and frequent encounters with other troops. A study by Sugimura et al (2000) also
supports this. The evidence that the
troop sizes in the northern areas of Japan is smaller than the ones in the southern
areas (Masui, 1988) might also contribute to these differences, because the
smaller the troop size, the fewer chances of social contact with others.
There is numerous
evidence of culture in JM. They
invent and transmit new behavior through imitational learning. They have learned various behaviors,
such as potato washing, wheat washing, swimming and some others.
Potato washing: was first
started by a one and a half year old female macaque named “Imo” (means sweet
potato in Japanese) in 1953 (Kawai, 1990/1993). She found a sweet potato thrown on the beach, took the
potato and washed the sand off by using river water. Her behavior was first imitated by her siblings and mother,
then later by all members of the troop except the leader of the troop (Kawai,
1990/1993; Napier & Napier, 1985).
The washing behavior later evolved into the seasoning behavior. At first potato washing was simply used
to wash off the sand, but the later mode of potato washing was used to season
the potato with salty sea water.
They bit rather briefly the first time, and then they dipped the potato
into the seawater to season it and bit it again (Kawai, 1990/1993). Imo also started the wheat washing
behavior. She made a ball with
wheat and sand and threw it into the water, then picked up only the wheat that
would float up (Kawai, 1990/1993).
This behavior was spread to most members of the troop. Swimming behavior also spread by
imitational learning (Kawai, 1990/1993; Napier & Napier, 1985). One day, a researcher threw a potato
accidentally into the sea and one juvenile macaque dove into the sea to catch
it. Later the behavior spread
among the troop and now they even swim for recreation.
Another behavior spread
by imitational learning is the begging behavior. JM of Koshima inlet beg local people for food by raising a
hand to them (Kawai, 1990/1993).
Monkeys of INP, Arashiyama do the same behavior. They reached out for peanuts and bananas,
which my girlfriend bought at the small concession stand (Personal
observation). Stone-play was also
started and spread among juvenile macaques, and it is now popular at Arashiyama
(Huffman, 1991a; Personal observation).
Shellfish eating in Koshima inlet was started by a JM and now, most of
the macaques in Koshima inlet eat shellfish (Kawai, 1990/1993). Transmission of new grooming techniques
through imitation was reported by Tanaka (1998). A new louse egg-handling technique was invented by a female
during grooming and diffused among a free-ranging troop of JM.
Japanese macaques are one
of the most interesting primates to study due to these various aspects of
unique characteristics. They are
not only interesting research subjects, but also very friendly and fun to watch
and “play with.” They are used to
human beings, thus I would like everybody to take advantage of their
friendliness to interact with this exceptional species and discover the wonder
of nature.
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