David S. Sprague

Reproduction of Wild Japanese Macaque Females of Yakushima and Kinkazan Islands: A Preliminary Report

Wild Japanese macaque females of the Yakushima and Kinkazan populations exhibited similar reproductive features. (1) Births/female/year (BR: 0.27–0.35) was lower than those of provisioned troops, but (2) infant mortality (IM: 0.23–0.25) was higher than those of provisioned troops. (3) The interbirth interval (IBI) following the death of infants was 1.5–1.6 years, shorter than that following surviving infants (2.2–2.4 yrs). (4) Birth sex ratio (BSR) did not differ from 1∶1. There was no consistent correlation between (5) female age and IM, (6) maternal rank and offspring BSR, or (7) maternal rank and reproductive success. On the other hand, (8) BR of Yakushima females was significantly lower than that of Kinkazan females. In particular, (9) Yakushima females stopped reproduction earlier than Kinkazan females, although (10) the first birth of Yakushima females was about one year earlier than Kinkazan females. (11) BR exhibited a humped curve against female age in Yakushima, but it was uncertain whether old-aged females of Kinkazan exhibited a post-reproductive life span (PRLS). (12) The survivorship for female juveniles was lower than that for male juveniles in Yakushima, whereas the survivorship for male juveniles was lower than that for female juveniles in Kinkazan. These data may indicate that Yakushima females more severely compete for resources than Kinkazan females, because of high population density, whereas the population density of Kinkazan might be limited by climate (e.g. heavy snow) rather than density dependent ecological effects.

Male life history in natural populations of Japanese macaques: Migration, dominance rank, and troop participation of males in two habitats

This paper compares male life history parameters of two populations of Japanese macaques (Macaca fuscataBlyth, 1875), studied without provisioning: Yakushima (M. f. yakui), a subtropical forest habitat in southwestern Japan, and Kinkazan (M. f. fuscata), a temperate, deciduous forest habitat in northeastern Japan. The males of the two sites experienced similar life histories with respect to several traits. Age at natal dispersal was at about 5 years. Average troop residence was about three years. Most males joined troops at the bottom of the rank order, although a few males joined troops at the top rank. Dominance ranks of males tended to rise with the death or departure of higher ranking males. Visiting males accounted for about 41% of observed mating at both sites. However, the two sites differed in the sex ratio of troops, partly because a larger proportion of males apparently lived outside of troops in the Kinkazan site compared to Yakushima. In particular, non-natal young males were absent from the main study troop at Kinkazan. Large within-species variation may exist in the degree to which males associate with troops.

Intertroop transfer and dominance rank structure of nonnatal male Japanese macaques in Yakushima, Japan

We examined the interaction between intertroop transfer and male dominance ranks in a wild population of Japanese macaques (Macaca fuscata yakui) in Yakushima using data collected over 15 years. Intertroop transfer tended to maintain a linear, stable, and age-graded dominance rank order among nonnatal males irrespective of variation in troop size or composition. All males that joined a troop at the top of the rank order were prime adults. Among males joining at lower ranks, entry at the most subordinate position in the hierarchy was common. Males joining at lower ranks tended to join troops in which all other resident males were the same age or older. Adult males tended to join troops with few or no males. Young males tended to join troops with many resident males, and in which a relatively large proportion of males was other young ones. Intertroop transfer was responsible for most rank changes of resident males. The most common cause of males rising in rank was the emigration or death of a higher-ranking male. Males fell in rank most frequently as a result of a new male joining the troop at the top of the hierarchy. Rank reversals among resident males were rare. The cumulative effects of male transfers produce sociodemographic variation within a troop over time and sociodemographic diversity among troops in a local population. A key feature of intertroop diversity is that larger troops have a significantly greater proportion of young males than smaller troops. This diversity also creates the potential for intertroop variation in the severity of male competition and provides a range of options for transferring males.

Winter Range Utilization of a Japanese Macaque Troop in a Snowy Habitat

The winter range utilization pattern of a Japanese macaque troop in a snowy habitat was studied. The vegetation areas essential for subsistence were found to be relatively undisturbed mixed and deciduous forests. The concept of essential resource area (ERA) is defined. Our comparison among three troops in the same habitat in the past and present with different population densities indicated that the per capita ERA is quite important in determining the range area. This implies that the population and range area are resource-correlated.

Does Troop Size of Wild Japanese Macaques Influence Birth Rate and Infant Mortality in the Absence of Predators

For the wild Japanese macaques of Yakushima and Kinkazan Islands, we analyzed the relationship between the troop size or the number of adult females of each troop, infant/adult female ratio (IFR; crude birth rate), and infant mortality (IM) in habitats with no predators. In Yakushima, IFR was positively correlated to troop size and the number of adult females. In Kinkazan, however, IFR tended to decrease with the number of adult females. This difference may be due to the difference in troop size; i.e. in Yakushima, where troop size was small, IFR may increase with that of troop size, because a relatively larger troop is likely to the advantage in intertroop competition. In Kinkazan, where troop size was large, however, IFR is likely to decrease with troop size, because intratroop competition may increase. Thus, the present data roughly supportWranghams model of the social structure of female-bonded primates, and suggests that there is an optimal troop size for birth rate (BR). On the other hand, there was no clear correlation between IM and the troop size or number of adult females of each troop.

Field testing a global positioning system (GPS) collar on a Japanese monkey: reliability of automatic GPS positioning in a Japanese forest

A global positioning system (GPS) collar recorded the locations of an adult female Japanese macaque over a 9-day period in a habitat with mixed suburban and rural land-uses in Chiba Prefecture, Japan. The GPS device acquired positions even in forested areas. The GPS data located the female mostly in forested areas, although the female had ranged through a habitat with inter-mingled fields, orchards, quarries, and residential areas. However, the GPS position acquisition rate was low compared to studies carried out on North American mammals. The GPS fixed a position in 20% of positioning attempts. When the collared female was tracked by radio-telemetry, almost all failures of the GPS to fix a position occurred in forest.

Relative importance of within-habitat environment, land use and spatial autocorrelations for determining odonate assemblages in rural reservoir ponds in Japan

To clarify the major factors affecting odonate assemblages in rural reservoir ponds among within-habitat environments, land use around ponds and spatial autocorrelation, we surveyed odonate adults (Zygoptera and Anisoptera) in 70 study ponds in Ibaraki Prefecture, Japan, during three sampling periods in 2005. Redundancy analyses (RDA) for these three factor groups were executed to determine their strength in explaining the odonate species composition. Their relative contributions were also evaluated by the method of variation partitioning. A total of 41 odonate species were recorded in the study ponds, and 24 of them, excluding rare species, were used for our analysis. Summed effects including all three factor groups explained approximately 39% of the variation in odonate species composition. We found that spatial autocorrelation was the most important, though the within-habitat environment and land use had comparable effects. We conclude that spatial autocorrelation should be considered in this type of analysis, though we could not clearly explain what caused such a spatial structure. Pond area and debris that had accumulated at the bottom of ponds were selected as the within-habitat environment, and the forests and paddy fields around ponds were selected for land use after the procedure of forward stepwise selection. These results suggest that the recent decrease of forests around the ponds has had a negative effect on the odonate assemblages.

Mating Tactics in Response to Costs Incurred by Mating with Multiple Males in Wild Female Japanese Macaques

We investigated the costs of mating with multiple males in terms of feeding time, traveling distances, sexual proceptivity, and male aggression, for wild female (Macaca fuscata yakui) on Yakushima Island, Japan. We analyzed all-day focal sampling data from 7 females during the mating season (Sept.-Nov. 1996). On days when estrous females copulated with multiple males, they decreased their feeding time to half that of anestrous days, traveled longer distances, showed more proceptive sexual behaviors and received more aggression from subordinate males than on days when they copulated with only the 1st-ranking male. On days when females copulated with only the 1st-ranking male, they showed no difference in feeding time with that of anestrous days, and expended less effort than the above mating pattern because of short traveling distances, diminished sexual proceptivity and a lower frequency of aggression received. The results suggest that the costs of estrous vary according to female sexual proceptivity and the number and social status of mating partners. Female Japanese macaques exhibit a mixed mating strategy over prolonged estrous periods, which may provide females with opportunities to maximize the benefits of copulating with multiple males and to minimize the costs of estrus by mating with only the 1st-ranking male. During an estrous cycle, females may be adjusting efforts for reproduction and survival; i.e., mating vs. feeding.

Long-Term Research on Grauer’s Gorillas in Kahuzi-Biega National Park, DRC: Life History, Foraging Strategies, and Ecological Differentiation from Sympatric Chimpanzees

We have conducted long-term research on sympatric gorillas and chimpanzees in Kahuzi-Biega National Park since 1987. The demographic history of habituated gorillas has provided insights into their reproductive strategies. Infanticide by male gorillas, which has occurred frequently in the Virunga mountain gorilla population, had not been reported in Kahuzi for more than 20 years. However, soon after the large-scale killing of gorillas during a war in the late 1990s, it occurred three times within a few months. The infanticidal male might have discriminated between infants who were not his offspring and an infant whom he presumably sired based on past interactions with their mothers. At Kahuzi, births occurred most frequently during the period of ripe fruit abundance, and female Grauer’s gorillas show longer inter-birth interval than female mountain gorillas in the Virungas. A comparison of reproductive strategies among different gorilla populations suggests that seasonal fluctuation in food abundance may lead to slow reproduction, whereas the potential pressure of infanticide may promote rapid reproduction. The reduced ranges and increased encounters between unfamiliar groups induced by large human disturbance, such as wars or conversion of their habitat to farmland, might have produced conditions leading to infanticide.

Life History Tactics in Monkeys and Apes: Focus on Female-Dispersal Species

Primates show life history traits similar to those of cetaceans, such as small litter size, long gestation, long lactation, and long lifespan, in spite of striking contrasts in habitats, diet, mobility, and range size between them. Ecological factors (food and predation) may influence their life history traits in various ways, but social factors (social structure and reproductive strategies) may be more important for the life history of primates, in which both sexes live together even outside the breeding season. Group-living primates are classified into female-bonded species and female-dispersal species, based on the patterns of female dispersal after maturity. A comparison of life history parameters shows that female-dispersal species have a slower life history (gestation length, weaning age, age at first reproduction, and interbirth interval) than the female-bonded species, except for neonatal weight and weaning weight, which may be determined in relationship to female body weight. To elucidate factors promoting the slow life history, we focus on Atelinae and Hominidae (female-dispersal species) and examine their interspecific and intraspecific variation in social structure and male reproductive tactics in relationship to life history traits. Most Atelinae species form multimale and multifemale groups, and variation in their life history features may reflect relationships among males and their reproductive tactics. In howler monkeys, both males and females disperse, and infanticide by males may lead to a fast life history. In other Atelines, infanticide rarely occurs, although it has the effect of reducing interbirth interval. Forcible copulation by males occasionally occurs in spider monkeys. Variations in grouping among females reflecting their flexible foraging efforts according to distribution of high-quality foods may have some effects on the fast–slow continuum in the life history features of female Atelinae. Hominidae exhibit larger variations in life history features than Atelinae, probably because of their diverse social structure. Solitary nature and male reproductive tactics may have great influences on the life history of female great apes. Female orangutans, who usually live a solitary life, show the slowest life history. Maturing female orangutans need a longer time to establish their own home range and relationships with reproductive mates than female chimpanzees and gorillas, who transfer into other groups immediately after emigration. Female gorillas show the lowest age at first reproduction and the shortest interbirth interval. Intensive caretaking of the immature by male gorillas may facilitate early weaning, and infanticide by males may promote a prolonged bonding between a protector male and females to shorten the interbirth interval. Similar life history traits have been found in four long-term study sites of chimpanzees. Only females at Bossou show a fast life history, probably the result of high-quality foods and single male group composition under isolated conditions. The more frequent and stable association between females and males and more promiscuous mating in bonobos may facilitate the search for mating partners and lead to a shorter interbirth interval than chimpanzees. Frugivorous orangutans and chimpanzees may suffer more costs of female dispersal through decreased foraging efficiency than folivorous gorillas, and chimpanzees with fission–fusion grouping may suffer more social stress than gorillas in highly cohesive groups. Such differences may generally shape the fast–slow continuum of life history in female-dispersal primate species.