International Journal of Primatology, Vol. 21, No. 4, 2000
Socioecological Context of Parturition in Wild
Japanese Macaques (Macaca fuscata) on
Yakushima Island
Ruth Thomsen1 and Joseph Soltis2
Received May 5, 1999; revision December 16, 1999; accepted January 18, 2000
Female primates may adopt special feeding, foraging, and social strategies
around the time of giving birth. We observed 8 females during the prepartum
period, the day of birth, and the postpartum period in a wild troop of Japanese
macaques (Macaca fuscata yakui) on Yakushima Island, Japan. We collected
data on their activity budgets, quantitative feeding and foraging behavior,
and on female-male interactions. On the day of birth, females spent less time
moving and feeding, and more time resting relative to other periods. Overall
dietary diversity as well as arthropod foraging also decreased on the day of
birth. Females fed mostly on mature leaves, new leaves and shoots during
prepartum periods but mostly on fruit during postpartum periods. Decreased
feeding on leaves and increased feeding on fruit probably changed as a result
of seasonal availability, independently of parturition. Feeding on flowers,
fungi and other items remained constant over all periparturitional periods.
On the day of birth, new mothers had fewer social interactions with males
and spent more time out of proximity with other adults than in other periods.
Females rejected grooming presentations from males, groomed less with
males, spent less time ⱕ3 m of males, and received less aggression from
males on the day of birth. In the postpartum period, interactions with males
returned to prepartum values. Grooming with females did not differ across
the three periods. These results suggest that interactions with males may be
costly for females on the day of birth.
KEY WORDS: wild Japanese macaques; birth-giving; feeding and social behavior; male’s
role; Yakushima.
1
Department of Zoology, LM-University of Munich, Luisenstrasse 14, 80333 Munich, Germany. E-mail: 320084691601-0001@t-online.de (Ruth Thomsen).
2
Department of Anthropology, University of California, Los Angeles, California 90095, USA.
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0164-0291/00/0800-0685$18.00/0  2000 Plenum Publishing Corporation
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Thomsen and Soltis
INTRODUCTION
Studies of reproductive success in primates and other animals have
emphasized the importance of female access to food resources and male
access to females (Wrangham, 1980; van Schaik and van Hooff, 1996; Suzuki
and Tsukahara, 1996). With the exception of some primate species in which
males or older siblings contribute to parental care (Garber, 1997), female
primates are solely responsible for rearing their young. Thus, the quality
of maternal care, including feeding and social behavior around the time of
birth, should also have an important impact on female reproductive success.
Studies concerning parturition in primates have mainly focused on
patterns of social behavior (Macaca mulatta: Brandt and Mitchell, 1973;
Theropithecus gelada: Dunbar and Dunbar, 1974; M. fascicularis: Kemps
and Timmerman, 1982; Gorilla gorilla beringei: Stewart, 1984; Papio cynocephalus cynocephalus: Condit and Smith, 1994). Only two reports take
into account the feeding behavior of the new mother (Macaca sinica: Ratnayeke and Dittus, 1989; M. fuscata yakui: Thomsen, 1997). This bias stems
from the fact that most studies have concerned captive or provisioned
animals in which observations of natural feeding behavior is not possible.
We describe the feeding and social behavior of mothers around the
birth period for wild, unprovisioned Japanese macaques (Macaca fuscata
yakui) on Yakushima Island, Japan. We observed 8 females during their
individual periparturitional periods between March and June 1998. We
examined the changes in their activity budgets, the quality, quantity and
diversity of their diets, and their social behavior.
Japanese macaques are female-bonded primates, where a female’s
strongest relationships are with her close female kin (Itani, 1972; Pusey
and Packer, 1987; Davies, 1992). Studies of the relationship between female
and male Japanese macaques have mainly concerned mating strategies
(Enomoto, 1978; Huffman, 1992; Soltis et al., 1997). Affiliative relationships
between females and males during the birth season have also been observed
by Takahata (1982), though, infanticide was suspected in this population
(personal observations). Therefore, we focused on social interactions between parturient females and adult males.
METHODS
Study Site and Subjects
Yakushima Island (30⬚20⬘N; 130⬚30⬘E) constitutes the southern limit
of the distribution of Japanese macaques and its population is an endemic
Socioecological Context of Parturition in Wild Japanese Macaques
687
subspecies, Macaca fuscata yakui (Yakushima macaque). The mating period
is from September to February, and the birth period from March to July.
The monkeys have no natural predator. The diversity of plants is very high
for a temperate forest, with evergreen as well as deciduous tree species.
The vegetation types include primary forest, mixed primary and secondary
forest, secondary roadside forest and coastal vegetation (Maruhashi, 1980;
Hill, 1997).
We studied the well-habituated NINA-A troop, whose home range
extended from sea level to about 220 m asl and covered an area of about
1.4 km2. A single road transected the range. Records of troop composition
and male transfers have been kept since 1994 (T. Tanaka; Yakushima
Research Group). We studied the NINA-A troop continuously from September 1997 to December 1998. At the beginning of the study, the troop
consisted of 52 monkeys, including 15 adult males, and 15 adult females.
All adults and nearly all subadults could be distinguished individually by
each observer. At the beginning of the 1997 mating season, 4 females were
lactating, 3 were considered nulliparous (estimated 4–6 years with no living
offspring), and 8 females were parous, each with at least one living offspring
in the troop. All nonlactating and ⱖ2 lactating females copulated in the
1997 mating period.
Data Collection
In order to examine behavior around the time of parturition, we restricted systematic data collection to 3 periparturitional periods as follows.
(1) The prepartum period, which began 25 days before the estimated day
of birth and ended two days before, (2) the day of birth, (3) the postpartum
period, which began the second day after birth and ended 25 days thereafter.
We excluded two additional periods—the day preceding and the day after
the day of birth—due to lack of data. We estimated birth days so that
prepartum behaviors could be recorded for pregnant females. Although
female Japanese macaques often experience more than one estrus during
the mating period, most conceive from their first ovulation (Mitsunaga et
al., 1992). We calculated the probable birth range by counting forward 173
days from the first day and last day of each female’s first mating period
(Nigi, 1976; Mitsunaga et al., 1992). For prepartum periods, we followed
the 11 nonlactating females and 2 control—lactating—females from midMarch to beginning of June 1998. Five parous females, 2 primiparous females and 1 control female delivered during the study period (N ⫽ 8 births).
We excluded females that did not give birth from data analysis. When a
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newborn was detected, we recorded the date, time of detection, sex of the
baby and the absence of the placenta or placentophagia.
We recorded data using focal-animal sampling with 1-min point-sampling (Altmann, 1974) for 6 hrs per day for ⱖ2 days in the pre- and postpartum periods for each female. On the day of birth, we conducted focalanimal sampling for as long as possible, given the steep terrain, but always
for ⱖ3 hrs without interruption. For statistical analysis, we used 331 observation hrs (19860 points; range: 2250–2700; mean ⫾ SD: 2467.5 ⫾ 134.9 points
per female) on the 8 females (range: 37.7–45.0, mean: 41.12 ⫾ 2.25 hrs)
over the 3 periods (prepartum period: range: 12–18; mean: 17.25 ⫾ 2.12
hrs; day of birth: range: 3.0–9.0; mean: 6.15 ⫾ 1.85 hrs; postpartum: mean
18.0 ⫾ 0.0 hrs). RT conducted 316 hrs 30 min over all periods. Soltis
conducted an additional 14 hrs 30 min when newborns were observed in
the absence of Thomsen (N ⫽ 3).
Activity Budget
At each minute point-sample, we recorded one of the following activities: feeding (processing and eating food items), moving (all locomotor
activities on the ground and in trees, except for those related to aggression),
grooming (of and by others, excluding self-grooming), resting (sitting or
lying down without grooming). For each period, we calculated the percentage of time a female spent in each activity or in proximity with other
individuals by summing the points for each activity and dividing by the
sum of all points.
Feeding Behavior
We know most of the major plant food species when we began systematic data collection. When a focal female was feeding, we recorded the
species and the part consumed at each point sample. We distinguish 6 broad
categories: (1) fruit and seeds, (2) mature leaves, (3) young leaves, buds
and shoots, (4) flowers (5) fungi and (6) other: pith, bark, lichen, leaves
and stem of vines, fern, moss, grass and soil. We calculated percentage of
feeding time on each food category as we did for activity budgets.
Foraging and Feeding on Arthropods
We analyzed foraging and feeding on arthropods separately from the
other feeding records. To measure arthropod foraging and feeding activity,
Socioecological Context of Parturition in Wild Japanese Macaques
689
we used a hand-held counter to record each searching bout in a potential
arthropod patch (foraging) and each grip on an arthropod followed by
hand-to-mouth motion by a focal female (feeding). We recognized the
following arthropod patches: bunches of dried hanging leaves, dried ferns,
beneath bark of rotten or live trees, within rotten trees, within small
branches (for ants), and under mature leaves, stones or the crash barrier
near the road. We calculated each female’s arthropod foraging rate for
each period per hour of active behavior: feeding and moving.
Dietary Diversity
We made a daily food list for each female. For each period, we calculated the number of plant species consumed per 6 hours of observation.
The complete food list (38 spp. of 26 families) is available upon request.
Social Contact and Female–Male Relationships
We calculated the percent of time females remained alone: 3 m away
from other adults. We also recorded (1) female rejection of male grooming
presentations, (2) male-to-female aggressive interactions per hour, (3) the
percentage of time females were ⱕ3 m of a male, (4) the percentage of
time grooming with males, and (5) the percentage of time grooming with
females. Because aggressive behaviors are rare and short-lived, we recorded
all occurrences of aggression during focal samples. Aggressive behaviors
included noncontact (lunge, open-face threat, chase) and contact aggression
(bite, cuff).
Statistical Analysis
We used Friedman’s test for differences across the 3 periparturitional
periods and Dunn’s procedure to compare specific periods (Conover, 1980)
via in InStat 2.01 for Macintosh. All p-values presented are two-tailed, with
significance set at p ⬍ 0.05.
RESULTS
Activity Budgets
The time females spent in each of the 4 activities differed across the 3
periparturient periods. Compared to the prepartum and/or the postpartum
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periods, the day of birth was characterized by a decrease in the time spent
feeding, moving and grooming, and an increase in the time spent resting
(Table I).
Quantitative Feeding Behavior
Feeding on arthropods, fruit, mature leaves, new leaves and shoots,
and overall dietary diversity differed across the 3 periods. Time spent
feeding on flowers, fungi and other items, however, remained at a constant,
low level of around 5% (Table II). On the day of birth the arthropod
foraging rate as well as the overall dietary diversity decreased. The percent
of feeding time on fruit showed an increase across the three periods. By
contrast, feeding on leaves and shoots was high in the prepartum period,
but lower on the day of birth and in the postpartum period (Table II).
Additionally, placentophagia occurred in 2 of the 8 females in the early
morning hours. We saw no placenta when we first detected the other
6 babies.
Social Interactions and Female-Male Relationships
Most measures of social interaction varied across the three periparturitient periods (Table III). On the day of birth, females spent more time
Table I. Activity budget of periparturitional females (N ⫽ 8)a
Activity
1. Feeding time (%)
Dunn’s post test,
p ⬍ 0.05
2. Moving time (%)
Dunn’s post test,
p ⬍ 0.05
3. Resting time (%)
Dunn’s post test,
p ⬍ 0.05
4. Grooming time
(%)
Dunn’s post test,
p ⬍ 0.05
Friedman’s
test
(df ⫽ 2)
A
prepartum
B
day of birth
C
postpartum
Fr ⫽ 12.250
p ⫽ 0.0009
34.3 ⫺ 45.1
38.4 ⫾ 3.3
B
7.4 ⫺ 13.5
10.6 ⫾ 1.9
A and C
32.3 ⫺ 40.3
36.4 ⫾ 2.55
B
Fr ⫽ 14.000
p ⫽ 0.0001
16.1 ⫺ 29.3
22.01 ⫾ 4.2
B
10.0 ⫺ 17.2
13.44 ⫾ 2.34
A
13.3 ⫺ 21.10
16.9 ⫾ 2.8
Fr ⫽ 13.00
p ⫽ 0.0003
10.8 ⫾ 23.5
16.7 ⫾ 3.86
B
51.0 ⫺ 78.0
60.56 ⫾ 9.7
A and C
12.0 ⫺ 28.9
18.12 ⫾ 5.24
B
Fr ⫽ 9.750
p ⫽ 0.0048
18.0 ⫺ 29.0
22.62 ⫾ 4.34
0.0 ⫺ 26.6
15.8 ⫾ 9.8
C
20.0 ⫺ 37.0
28.12 ⫾ 49
B
Range of percentages, mean ⫾ SD. Significant differences between the 3 periparturitional
periods are indicated by A, B, or C in the rows labeled Dunn’s post test.
a
Fr ⫽ 7.750
p ⫽ 0.0179
Fr ⫽ 9.250
p ⫽ 0.008
Fr ⫽ 6.250
p ⫽ 0.0469
all NS
6.0 ⫺ 12.0
7.75 ⫾ 2.43
B
Fl. 0.0 ⫺ 8.2; 2.4 ⫾ 2.7
Fu. 4.8 ⫺ 14.8; 7.4 ⫾ 2.9
Oth. 1.4 ⫺ 23.3; 6.7 ⫾ 7.4
12.2 ⫺ 43.2
26.27 ⫾ 11.35
C
18.1 ⫺ 51.0
36.91 ⫾ 10.72
B and C
10.0 ⫺ 40.6
20.35 ⫾ 10.16
B
6.2 ⫺ 12.1
9.1 ⫾ 2.0
Fr ⫽ 14.250
p ⫽ 0.001
Fr ⫽ 8.600
p ⫽ 0.0099
A
prepartum
Friedman’s test
(df ⫽ 2)
0.0 ⫺ 42.0
18.5 ⫺ 15.75
A
0.0 ⫺ 26.2
9.4 ⫾ 16.08
A
0.0 ⫺ 4.6
2.05 ⫾ 1.6
C
1.0 ⫺ 6.0
3.38 ⫾ 1.41
A
0.0 ⫺ 2.0; 0.66 ⫾ 0.93
0.0 ⫺ 15.6; 5.0 ⫾ 5.4
0.0 ⫺ 33.6; 7.8 ⫾ 11.39
0.0 ⫺ 77.3
33.86 ⫾ 28.12
B
day of birth
0.0 ⫺ 7.0; 3.6 ⫾ 3.2
0.0 ⫺ 13.0; 6.6 ⫾ 4.4
3.2 ⫺ 19.1; 10.3 ⫾ 6.3
26.1 ⫺ 72.2
53.14 ⫾ 17.99
A
7.5 ⫺ 32.4
16.03 ⫾ 8.7
A
2.3 ⫺ 13.3
10.25 ⫾ 7.4
3.8 ⫺ 30.1
16.7 ⫾ 8.9
B
5.0 ⫺ 10.0
7.5 ⫾ 1.93
C
postpartum
a
Range of percentages, mean ⫾ SD. Significant differences between the 3 peripartuitent periods are indicated by A, B, or C in
the rows labeled Dunn’s post test.
4. Fruit
(% of feeding time)
Dunn’s post test, p ⬍ 0.05
5. Mature leaves
(% of feeding time)
Dunn’s post test, p ⬍ 0.05
6. New leaves and shoots
(% of feeding time)
Dunn’s post test, p ⬍ 0.05
1. Arthropod foraging
rate (grips/hour)
Dunn’s post test, p ⬍ 0.05
2. Dietary diversity
(within 6 hr)
Dunn’s post test, p ⬍ 0.05
3. Flower, fungi, and
other (% of feeding time)
Ecological context
Table II. Ecological context of parturition (N ⫽ 8 females)a
Socioecological Context of Parturition in Wild Japanese Macaques
691
0.0 ⫺ 20.0
6.36 ⫾ 7.87
B
0.000 ⫺ 0.333
0.135 ⫾ 0.106
B
9.1 ⫺ 21.1
15.1 ⫾ 4.2
B
0.0 ⫺ 14.1
5.52 ⫾ 4.96
B
10.0 ⫺ 25.4
17.61 ⫾ 5.31
32.3 ⫺ 48.4
38.6 ⫾ 5.2
Fr ⫽ 13.067
p ⫽ 0.0001
Fr ⫽ 10.750
p ⫽ 0.0024
NS
Fr ⫽ 10.867
p ⫽ 0.0011
Fr ⫽ 9.2500
p ⫽ 0.008
Fr ⫽ 11.385
p ⫽ 0.0011
A
prepartum
Friedman’s test
(df ⫽ 2)
66.6 ⫺ 100
95.82 ⫾ 11.81
A and C
0.0 ⫺ 0.0
0.0 ⫾ 0.0
A and C
0.0 ⫺ 16.1
5.4 ⫾ 5.1
A and C
0.0 ⫺ 0.0
0.0 ⫾ 0.0
A
0.0 ⫺ 26.4
15.81 ⫾ 9.8
32.5 ⫺ 86.9
49.6 ⫾ 18.4
C
B
day of birth
13.4 ⫺ 36.5
24.6 ⫾ 7.6
27.9 ⫺ 60.5
36.3 ⫾ 10.7
B
0.0 ⫾ 12.5
3.49 ⫾ 5.05
B
0.0 ⫺ 0.222
0.111 ⫾ 0.066
B
6.2 ⫺ 23.3
15.4 ⫾ 5.2
B
0.0 ⫺ 7.1
3.89 ⫾ 2.87
C
postpartum
a
Range of percentages, mean ⫾ SD. Significant differences between the 3 periparturient periods are indicated by A, B, or C in
the rows labeled Dunn’s post test.
Dunn’s post test, p ⬍ 0.05
4. Groom with
males (%)
Dunn’s post test, p ⬍ 0.05
5. Groom with
females (%)
6. Females being
alone (%)
Dunn’s post test, p ⬍ 0.05
1. Groom rejection
of males (%)
Dunn’s post test, p ⬍ 0.05
2. Aggression with
males/hour
Dunn’s post test, p ⬍ 0.05
3. Males ⬍3 m (%)
Social context
Table III. Social context of parturition (N ⫽ 8 females).a
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693
ⱕ 3 m of other adults than in the postpartum period. Also, rejection of
grooming presentations from males increased dramatically on the day of
birth. Further, grooming with males, aggression received from males, and
time spent ⱕ3 m of males all decreased on the day of birth compared to
the perpartum and/or postpartum periods. Conversely, time spent grooming
with females did not differ across the three periods (Table III).
DISCUSSION
Activity Budget and Ecological Context
The prepartum period was characterized by particularly long times
spent feeding on mature and young leaves and high dietary diversity. This
finding reflects the general pattern observed among Yakushima macaques
of the warm temperate forest, in which time spent feeding is positively
correlated with leaf feeding, and the more Yakushima macaques feed on
leaves the higher dietary diversity becomes (Hill, 1997). In the postpartum
period, lactating females consumed more fruit and seed than in the prepartum period; thus, dietary diversity was lower. Quantitative food selection
is dependent on availability (Agetsuma, 1995), and in general Yakushima
macaques prefer to feed on ripe fruit, which mainly is available in autumn
and early winter (Hill, 1997). They change to leaves during late winter and
spring if fruit become scarce. The female feeding pattern prepartum as well
as postpartum reflects this rule for omnivorous primates (Harrison, 1984)
and may not be closely related with parturition.
On the day of birth, females spent more time resting and less time
moving and feeding than before and after birth. Such extreme reduction
in feeding time on the day of birth, from around 40 to 10%, was previously
reported for periparturitional Yakushima macaques by Thomsen (1997)
and may be similar for other primate species. Females that give birth
may require increased resting time, which may be achieved by reducing
feeding to minimal levels and by reducing moving time to the minimum
required to keep up with the troop. Arthropod foraging may have
decreased because it is incompatible with carrying a newborn infant. In
the two cases where in the first detection of the newborn occurred early
in the morning, placentophagia occurred. Placentophagia occurs in other
wild primates (Dunbar and Dunbar, 1974; Ratnayeke and Dittus, 1989)
and may help to compensate for the lack of nutritional intake on the
day of birth (Brandt and Mitchell, 1971).
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Social Strategies
On the day of birth, females reduced the time spent ⱕ3 m of other
adult troop members. Overall interaction with males was greatly reduced.
Time spent with males, grooming with males, and aggression received from
males, all decreased on the day of birth. Moreover, females dramatically
increased rejection of male grooming presentations from about 5 to 95%.
Grooming received from other females, however, did not differ across the
periparturient periods. This suggests that interactions with males are costly
in parturient contexts.
There is potential for both costly and beneficial interaction with males
in Japanese macaques. Aggression from males towards infants occurs in
primates, e.g., Macaca mulatta (Brandt and Mitchell 1973; Rawlins 1979),
and infanticide is often part of male reproductive strategy (Hrdy et al.,
1995). Furthermore, Soltis (in press) observed male attacks on infants and
one case of infanticide in the study population.
Conversely, affiliative male-female relationships in the birth season
also occur in provisioned Japanese macaques. Females may benefit from
cofeeding with males when food is clumped (Grewal, 1980; Takahata, 1982).
Since females reduced feeding time on the day of birth and clumped food
is rare in this habitat, females may have little demand for cofeeding benefits
immediately after parturition. Our findings suggest that at least on the day
of birth the costs of being close to males outweighs any presumed benefits.
In the postpartum period interactions with males returned to prepartum values. It is possible that benefits of male interaction, e.g., protection
from infanticide or cofeeding opportunities, outweigh costs at these times
with vulnerable infants.
ACKNOWLEDGMENTS
We would like to thank Naohiko Noma for teaching plant identifications and Toshiaki Tanaka from Yakushima Research Group for providing
data on the study troop. We also thank Sachiko Hayakawa, Miki Matsubara
and Hideki Sugiura for their cooperation in the field on Yakushima Island
and at the PRI. We received very helpful comments and critical advise on
an earlier draft of the manuscript from Mike Huffman, David Hill, Volker
Sommer, and Juichi Yamagiwa. RT furthermore wants to thank Juichi
Yamagiwa and Hideyuki Ohsawa and the PRI for continual support. JS
thanks Yukimaru Sugiyama and Juichi Yamagiwa for their continual support. RT was financed by a grant (HSP III) from the German Academic
Socioecological Context of Parturition in Wild Japanese Macaques
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Exchange Service (DAAD) and JS by the USA National Science Foundation and the Japanese Society for the Promotion of Science.
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