On the acquisition and propagation of a new food habit in the natural group of the Japanese monkey at Takasaki - Yama

Summary

This paper reports how the wild Japanese monkeys at Mt. Takasaki-Yama (City of Oita, Kyusyu) adapted themselves, in terms of food habits, to the change of environments, which was caused by the contact with men.

This report contains following problems; 1) acquisition of new food habits, namely one of acculturation problems, 2) the difference in the acquiring capacity of new habits with references to age and sex, 3) the diffusion of new habits among the group members, 4) relation between the diffusion and the social structure of the group, 5) problems about inter — and intra — communication.

This group of Takasaki-Yama was first provisionized with sweet potatoes, wheat and apples in November 1952. At the beginning of provisionization, the monkeys there ate sweet potatoes and wheat but not apples. Howewer, they gradually get used to apples and now eat them. In January 1953, peanuts were given to them. It took four months for the whole group to start eating them, although they did not eat at all at the beginning. Summer oranges (natumikan in Japanese), damsons and soy beans were likewise accepted as their new food. These food materials were accepted relatively rapidly. On the contrary boiled rice, bread, biscuits and candies were difficult to be accepted. The monkeys are quite indifferent to them even now, though five and a half years has already passed since the beginning of provisionization and a great many sightseers have been giving them to the monkeys every day just like in a zoo.

From the above mentioned observations, candies were thought to be the most appropriate food material to be used for the investigation on the acquisition process of new food among monkeys. Candies were not quite new to the monkeys in July 1954, because sightseers had been giving them quite a lot. However there were very few who ate the candies at that time.

In this test the monkey's reaction to candies were classified according to the degree of interest and the following three categories were adopted; 1) paid no attention and did not eat at all; 2) showed interest but did not eat; 3) showed interest and ate. The method of test was quite a simple one. Having given candies to every individual who was identified, its reaction was observed. Six series of tests were conducted as follows from July 1954 to September 1955.

1st test......July 11–14, 1954 4th test......May 6–14, 1955

2nd test......August 20–30, 1954 5th test......July 3–15, 1955

3rd test......March 22–28, 1955 6th test......September 12–30, 1955

Results:

• 1. Adult and young males. At the first test only 3 out of 37 (8.1 %) ate the candies. At the 6th test, however, 13 out of 40 (32%) ate them. The rate of acquiring the new habits are surprisingly low comparing with the females and the infants. Although in this case the rate of acquisition seems to be hardly influenced by their social class, the social structure seems to have some influence on it (Tab. 2).

• 2. Adult and young females. At the first test 1 out of 66 (1.5%) and at the 6th test 42 out of 82 (51.2%) ate the candies. As these figures show, there is a great difference in the percentage between adult female and male, which seems to be caused by the fact that females have infants whose acquisition rate is high. Adult females are grouped into the following three classes according to age; 1) young adult females of 4–6 years old, 2) middle-aged females of about 7–16 years old, 3) old females. At the 6th test, 72.7% of young adult females, 46.4% of middle-aged females and 36.8% of old females were seen to have acquired the new habit. From these facts, it will be said that, the younger females are more adaptable to the new environments than the older (Tab. 3).

• 3. Infants. The infants from a yearing to 3 years have very high rate to acquisition. At the first test more than 50% of them ate the candies, and at the 6th test 92.3% of the 3, 4 years (born in 1951 and 1952), 88.9% of the 2 years (born in 1953) and 100% of the one year (born in 1954) ate them (Tab. 4).

  Discussion:

• 1. The acquisition of new food habits will be caused either by discovery or imitation. It is difficult to determine exactly whether it is caused by discovery or imitation, but in the case of adults it may be said that imitation rather than discovery will be the main process, because and individual who has close contact with infants (whose acquisition rate is very high) shows higher rate of acquisition, e. g., young males of higher rank who have close contact with infants in the social structure; subleaders who have special habits of raising infants in the breeding season of females; females who nurse a yearing.

• 2. The chief routes of diffusion by imitation in the group seem to be as follows;

• 1) infants →their mothers

• 2) infants →subleaders or leaders who care them

• 3) adult females→their consorts (in the mating season)

• 4) adult females→adult males who are in the fairly constant grooming relation with them

• 5) adults →their mothers

• 6) younger brothers and sisters→elder brothers and sisters

• 3. This diffusion process may be regarded as a sort of communication in which communicators have no intention of communicating. This communication depends solely on communicatees. Therefore it should be named “imitation”.

• 4. The food habit which is reported in this paper is not native but acquired. It, therefore, can best be called aculture of the monkey society.

• 5. Transmission of the culture of a group to another group is not likely because, while it needs intimate contact between groups, groups of wild Japanese monkeys are very closed and do not have contacts with one another excepting the next case.

• 6. Sometimes so-called “solitary” may move from one Group to another. In that case transmission will be likely because he may carry the habits with him.