DEMOGRAPHIC DATA OF WILD JAPANESE MONKEYS ON KOSHIMA ISLAND: PRELIMINARY

抄録

This paper summarizes demographic data from a troop of wild Japanese monkeys on Koshima island. The island measures about 32 ha, with a maximum elevation of 113 m, and is covered by semi-tropical forest. Imanishi and his colleagues began the long-term observation of Koshima monkeys on December 3, 1948. Since then, researchers have been provisioning and habituating monkeys, and continuously collecting demographic data and monthly body weight measurements from individual troop members. Currently, longitudinal records span eight generations of monkeys. During the 57-year period from 1952 to 2009, a total of 558 individual monkeys have been recorded: 290 males, 241 females, and 27 infants who died and disappeared before their sex could be determined. Therefore, the male to female sex ratio was 1.20. The body weight of males reached its maximum between the ages of 12 to 14 years (12-13 kg); in females maximum body weight was recorded between 7 to 8 years (6 to 8 kg). Individuals in this troop are thus smaller than average wild Japanese monkeys. The average age at which females first gave birth was 8.49 years, based on records from 128 individuals. Among these females, the average number of births per individual was 4.29. Infant mortality rate within the first year of life was 33.1% among male offspring and 29.2% among females. Further analysis has revealed differences in demographic parameters among family lineages.