Yukio Takahata

Social relations between adult males and females of Japanese monkeys in the arashiyama B troop

Some dyads of Japanese monkey adult males and females show remarkable spatial proximity and frequent exchanges of social behaviors. It is suggested that some kind of “affinity” exists between them. Females obtain much unilateral benefit from “proximity effects”; even lowranking females can dominate high-ranking females as long as they stay nearby their “affinitive” males. Males acquire female followers in return. Mating relations and female mother-daughter relations play important roles in forming new “affinitive relations.” Once monkeys have formed “affinitive relations,” however, they seldom mate with each other, as if they were kin-related. Therefore, the acquisition of female followers appears inconsistent with a males strategy for reproducing many genes in the next generation.

The Reproductive Biology of a Free-ranging Troop of Japanese Monkeys*

Quantitative data on the reproductive biology of Japanese monkeys (Macaca fuscata), especially of females, are reported here. Arashiyama B troop shows stable annual breeding periodicity, and has mating seasons between October and March. In mating seasons, females show estrus with rather consistent cyclicity, and are in estrus for a total of 35 days on an average. The mean length of estrous cycle is 34 days. Although most females show estrus inter-menstrually, some show peri-menstrually; i.e., estrus does not always synchronize strictly with ovulation. Pubescent females between 3.5 and 6.5 years show estrus, but with low sexual activity. Middle-aged females between 7.5 and 16.5 years show high sexual activity with high conception rate. Old-aged females over 17.5 years show low sexual activity. Females with surviving infants have lower sexual activity than those without infants. There is found no significant correlation between females ranking and sexual activity.

Reproductive parameters of female Japanese macaques: Thirty years data from the arashiyama troops, Japan

Over a 30-year period from 1954 to 1983, 975 live births were recorded for Japanese macaque females at the Iwatayama Monkey Park, Arashiyama, Japan. Excluding unknown birth dates, primiparous mothers gave birth to 185 infants (182 cases with age of mother known) and multiparous mothers gave birth to 723 infants (603 cases with age of mother known). The peak month of birth was May with 52.3% of the total births occurring during the period. Multiparous females who had not given birth the previous year did so earlier than multiparous females who had given birth the previous year and also earlier than primiparous females. Among the females who had given birth the previous year, females whose infant had died gave birth earlier than females who had reared an infant the previous year. The offspring sex ratio (1:0.97) was not significantly different from 1:1, and revealed no consistent association with mothers age. Age-fecundity exhibited a humped curve. The annual birth rate was low at the age of 4 years but increased thereafter, ranging between 46.7% and 69.0%, at between 5 and 19 years of age, but again decreased for females between 20 and 25 years of age. Some old females displayed clear reproductive senescence. The infant mortality within the first year of age was quite low (10.3%) and the neonatal (less than 1 month old) mortality rate accounted for 49.0% of all infant deaths. There was no significant difference between the mortality rates of male and female infants. A females rank-class had no apparent effect on the annual birth rate, infant mortality, and offspring sex ratio. These long-term data are compared with those from other primate populations.

Chimpanzee predation in the Mahale mountains from August 1979 to May 1982

Fifty-four episodes of predatory behavior of wild chimpanzees were recorded in Mahale, western Tanzania, from August 1979 to May 1982. The chimpanzees most frequently hunt in two seasons, during May, and from August to December. Longer-term fecal analysis indicates that predation frequency is significantly higher in the dry than in the rainy season. The seasonality of predation might be the result of the sum of various ecological factors, at least one of which is the birth season of the prey species. Most of the prey are juvenile blue duiker, bushbuck, bushpig, red colobus, and red-tailed monkeys. Sex difference is recognized in the prey selection and in the hunting method employed. Apparent local difference in the predatory behavior between Mahale and Combe chimpanzees (in Mahale,females hunt more frequently, and blue duiker is the most frequent prey) can be understood in terms of the difference either in the observation methods or in the faunal diversity and density. Other aspects of predatory behavior also are reported.

Adult Male Chimpanzees Kill and Eat a Male Newborn Infant: Newly Observed Intragroup Infanticide and Cannibalism in Mahale National Park, Tanzania

On 5 July 1983, the adult male chimpanzees of M group killed and ate a male newborn infant in Mahale National Park, Western Tanzania. The infant is believed to have been sired by one of the M group ma

Newly acquired feeding habits among the chimpanzees of the Mahale Mountains National Park, Tanzania

The M group chimpanzees (Pan troglodytes schweinfurthii) of the Mahale Mountains National Park, Tanzania, began to feed on three agricultural fruit species, guava, mango and lemon. It took them 7–8 years until they began to taste these fruits since the villagers left the park area in 1974. Although adult chimpanzees are conservative in their feeding habits, they are capable of rapidly acquiring new feeding habits, or new traditions, once they notice that the food is suitable.

A case of unusually early postpartum resumption of estrous cycling in a young female chimpanzee in the wild

A case of unusually early postpartum resumption of estrous cycling (<7 months) was recorded for a young, presumably primiparous female in the M group of chimpanzees (Pan troglodytes schweinfurthii) in the Mahale Mountains National Park, western Tanzania. The female showed estrous cycling while lactating her infant, and mated with young and low-ranking males as well as with the alpha male.