Demography and reproductive parameters of a free-ranging group of Japanese macaques (Macaca fuscata) at Katsuyama

Demographic and reproductive data were analyzed for a period of 28 years in the females of a free-ranging group of Japanese macaques at Katsuyama, Okayama Prefecture, Japan. The overall mean, age-specific fecundity rates were 5.43% for 4-year-olds and 41.86% for 5-year-olds, increasing to a peak of 66.67% for 13-year-olds. Fecundity remained relatively high (52.31–54.24%) in 16–19-year-olds, but decreased sharply (45.45–17.86%) in 20–23-year-olds, and became very low in 24–26-year-olds. Females aged 27 years or more did not produce infants. The average age at first birth was 5.41 years. Births peaked in mid-May. The timing of the first births each year remained essentially unchanged during the study period, whereas the timing of the median and last births shifted towards the later part of the season. The mean interbirth interval for all females was 1.56 years. The value was 1.54 years for multiparous females and 1.29 years for females following infant loss. These intervals were significantly shorter than those for primiparous females, and females with surviving infants. The overall mean infant mortality within the first year of life was 10.2%. The value was 8.6% for 10–14-year-olds, and 7.5% for 15–19-year-olds. The timing of birth differed among the four female matrilineal dominance rank-classes. The female fecundity rates increased as a function of matrilineal dominance rank. It is suggested that all demographic and reproductive data should be analyzed in detail with respect to the group's history.     

Feasibility of successfully breeding rhesus macaques (Macaca mulatta) to obtain healthy infants year-round

Rhesus monkeys are typically seasonal breeders but can be induced to extend the timing of their mating and births under captive conditions. The following analyses evaluated the potential impact of extending their pregnancies and deliveries year-round. Birth records from a large breeding colony housed in an indoor facility with a constant 14-hr light/10-hr dark cycle were analyzed across 25 years to examine seasonal trends in monkeys that mated in one of two ways: spontaneous in social groups or with a scheduled, timed-mating protocol. The dates of delivery and birth weights for 2,084 infants were used in these analyses. Younger nulliparous females mating in social groups evinced a clear seasonal peak when birthing their first infant. However, older females, both primiparous and multiparous, could be bred continuously, which enable the birth of infants in every month of the year. Based on the live birth rate, infant birth weights, high survival rates, and the normal sex ratio of infants birthed year-round, there were no adverse effects of breeding rhesus monkeys in this way. The continuous availability of infant births can be very advantageous for many types of research programs.     

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 mother's 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 female's 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.     

Reproductive patterns and birth seasonality in a South-American breeding colony of common marmosets,Callithrix jacchus

We analyzed data on captive-born and wild-caught females housed under natural conditions in a colony located in northeastern Brazil. No differences in reproductive performance were found between captive-born and wild-caught females. Twins were the most frequent litter size, followed by triplets and singletons. No parity effect was observed, with similar infant survival for nulliparous and multiparous females. No significant departures in sex ratio were detected for births and mortality of the male and female infants. The age of the females at the time of pairing showed a negative correlation with pairing-parturition length, but did not affect infant survival. The prolongation in pairing-parturition interval (PPI) and interbirth interval (IBI) was related to birth seasonality. The births were clustered in the second half of the dry season and the beginning of the wet season (November–March), and the time of pairing and the time of infant birth influenced the PPI and IBI, respectively. The use of outdoor cages, which allowed the animals to be aware of the seasonal variations in photo-period and rainfall seems to be sufficient to time the reproductive activity, even when the animals are maintained on a constant food supply.     

Differential reproductive success and facultative adjustment of sex ratios among captive female bonnet macaques (Macaca radiata)

In a group of captive bonnet macaques (Macaca radiata) housed at the California Primate Research Center, variance in reproductive success among females is primarily due to differences in infant survival. The infants of low-ranking females have a smaller probability of surviving to 6 months of age than do the infants of other females. In addition, the juvenile daughters of low-ranking females are more vulnerable to behaviourally induced mortality than are other immature animals. Observational evidence indicates that this mortality is the direct result of aggression by unrelated, higherranking adult females. Although infants' sex is not consistently related to survival, yearly fluctuations in the survival of male and female infants are reflected in the extent and direction of the skew in the sex ratio of offspring produced the following year. Years in which the highest proportion of male infants survive are followed by years in which the largest proportions of the birth cohorts are composed of males, and years in which the largest proportions of females survive are followed by years in which the largest proportions of birth cohorts are composed of females. For infant females the probability of surviving is reduced when a substantial proportion of the birth cohort is composed of females. The same pattern is evident among the sons of low-ranking females. The adaptive significance of behaviourally induced variation in reproductive success among females is considered in relation to these data.     

An analysis of birth sex ratio bias in captive prosimian species

The extent to which sex ratio bias is a common reproductive characteristic of prosimians has not been well established. The present study analyzed reproduction in 13 breeding groups of captive prosimians for evidence of birth sex ratio bias. A substantial male bias was demonstrated in nongregarious, but not gregarious, breeding groups. Analyses of birth sex ratios of individual mothers suggested that the observed bias did not result from the tendency of a few mothers to overproduce males, but rather from a small but reliable excess of male births in general. An examination of infant mortality revealed that male Otolemur garnettii and Microcebus murinus infants were more vulnerable to preweaning mortality, whereas female Eulemur fulvus albifrons infants were more vulnerable. An analysis of birth order by sex found that mothers of one group (O. garnettii) tended to produce males initially and females later. Additionally, a distinct pattern of birth seasonality was noted among Malagasy prosimians that was absent in the African prosimians. Greater length of period of sexual receptivity for nongregarious females as compared to gregarious females is proposed as a possible mechanism of male birth sex ratio bias. © 1996 Wiley-Liss, Inc.     

Factors associated with birth rate and live birth rate in multi-male breeding groups of rhesus monkeys

Reproductive records of 284 female rhesus monkeys housed in six multimale corrals at the California Primate Research Center were examined for the birth seasons 1977–1982 to determine possible associations between the probability of birth or live birth and female age, parity, origin, parturition in the previous season, infant birth date, and infant birth date in previous season. Multiple logistic regression analysis was used to identify and quantitate the effects of factors on the probability of birth or live birth, while controlling for the possibly confounding effects of other factors in the model. Females who had infants early in the previous season were 2.5 times as likely to give birth as those who had infants late in the previous season. Females with two or three previous births were 2.1 times as likely to give birth, and those with four or five previous births were 6.7 times as likely to give birth as were females with no or one previous birth. Controlling for other factors (age, parity, and timing of birth in the previous season), corralborn females were 3.3 times as likely to give birth as either wild-caught or domestic-born monkeys not native to the corrals. Domestic-born females who were not corral natives were 0.3 times as likely to have live births as wild-caught females. Births late in the season were 1.8 times as likely to result in live infants as births early in the season.     

Sex ratio and mortality in a laboratory colony of the common marmoset (Callithrix jacchus).

In a retrospective study sex ratio and mortality were analysed in a captive colony of common marmosets (Callithrix jacchus). Seven hundred and thirty-five infants in 294 litters (20 singletons, 119 twins, 140 triplets, 14 quadruplets) out of 57 breeding females were evaluated. The sex ratio at birth was 0.95 males:1.0 females. The frequency of males and females, as well as the sex composition of twins and triplets confirm the assumption of dizygotic twinning in the common marmoset. According to age at death, 9 categories were differentiated, with perinatal mortality being the highest. Once early infancy had passed the probability of a common marmoset infant of our colony reaching childhood is nearly 95%. Sixty per cent of all liveborn infants survived beyond 18 months. Mortality of infants at birth from primiparous mothers did not differ from that of pluriparous females, nor did the survival rate of infants with the filial generation the respective female had reached (F1 to F6). Females with a high ratio of triplets and quadruplets had a lower reproductive success than females with a majority of singleton or twin deliveries. Differential mortality between males and females was not observed. The frequency of stillbirths was not strongly related to parity, but was to litter-size. Most stillborn babies were seen in sets of quadruplets, most abortions in singletons. A normal socialization in a stable social environment, as well as not pairing the animals before they are fully adult, are considered important factors in good breeding success and infant survival.     

Reproductive parameters of wild Trachypithecus leucocephalus: seasonality,infant mortality and interbirth interval

Understanding the reproductive parameters of endangered primate species is vital for evaluating the status of populations and developing adequate conservation measures. This study provides the first detailed analysis of the reproductive parameters of wild white‐headed langurs (Trachypithecus leucocephalus), based on demographic data collected over an 8‐year period in the Nongguan Karst Hills in Chongzuo County, Guangxi, China. From 1998 to 2002, a total of 133 live births were recorded in the population based on systematic censuses. Births occurred throughout the year, but the temporal pattern was highly correlated with seasonal variation in temperature and rainfall, with the birth peak coinciding with the dry and cold months of November–March. The average birthrate was 0.47±0.13 births per female per year and mortality for infants younger than 20 months was 15.8%. From 1998 to 2006, 14 females gave birth to 41 infants in four focal groups. The average age at first birth for female langurs was 5–6 years (n=5) and the interbirth interval (IBI) was 23.2±5.2 months (median=24.5 months, n=27). Infants are weaned at 19–21 months of age. The IBI for females with infant loss before weaning was significantly shorter than those for females whose infants survived. It appears that birth seasonality in the white‐headed langurs is influenced by seasonal changes in food availability. The timing of conceptions was found to coincide with peak food availability. The reproductive parameters for white‐headed langurs reported here are quite similar to those reported for other colobine species. One major difference is our observation of lower infant mortality in Trachypithecus. Am. J. Primatol. 71:558–566, 2009. © 2009 Wiley‐Liss, Inc.     

Interannual variability in fruit abundance and the reproductive seasonality in Sumatran Long-tailed macaques (Macaca fascicularis)

In an environment with a seasonal food supply, most primate species show birth peaks which precede the peak food period by some two to five months. Sumatran Long-tailed macaques (Macaca fascicularis), however, showed birth peaks during or after the fruit peak. Years of high birth rates and early birth peaks alternated with years of low birth rates and late peaks. The timing of births was strongly influenced by a female's condition, which depends on food supply and her previous reproductive history. Pregnant females were more active than other females, whereas females with young infants were less active.
The unusual timing of births is ascribed to the unpredictability of the height of the annual fruit peak. This hypothesis is supported by the reproductive patterns of other South-east Asian primates and by a model comparing the two types of reproductive timing. Further differences between the two strategies of reproductive timing are predicted.     

Reproductive parameters of wild female Rhinopithecus roxellana

On the basis on 6 years of observation, we estimated the reproductive parameters of a Golden snub-nosed monkey (Rhinopithecus roxellana) group in the Qinling Mountains, China. We observed 88 births in 47 females from 2001 to 2006. Two methods were used to calculate the birthrate. The first method is based on the number of births observed in a year, giving 0.49+/-0.07 (mean+/-SD), and the second method is based on the female-years of observation, giving 0.49+/-0.17 births per female per year in this troop. The mean interbirth interval is 21.88+/-6.01 months (mean+/-SD). The mortality of infant born between 2002 and 2005 was 22.4%. The interbirth intervals of females that had lost an infant before the age of 6 months were significantly shorter than that of females whose infants survived for more than 6 months. A female usually gives birth once every 2 years if the previous offspring survives to a weaning age of 5-6 months, or will give birth in the next year if the previous young dies before reaching an age of 6 months. Births were significantly concentrated during March to May of each year. The mean birth date was on April 14, median was April 12; and the standard deviation was 13.98 days. Birth peak occurs 6-7 months after mating peak. From observations on 15 individuals that gave birth for the first time, we concluded that the wild female Golden snub-nosed monkeys in Qinling Mountains start giving birth at an age of 5 or 6 years. We suggest that the seasonal reproductive pattern is an adaptive response to the availability of seasonal food. Our results are consistent with the hypothesis that these reproductive characteristics are a result of adaptation to the seasonality of mountain climate and food resources.     

Factors Influencing the Reproductive Success of Female Black Howlers (<Emphasis Type="Italic">Alouatta pigra</Emphasis>)

Measuring reproductive success is necessary to determine an organism's fitness, and thus, to address evolutionary processes. In this study we determined the effects of social, ecological, and individual attributes on the reproductive success of black howlers (Alouatta pigra) measured through infant survival and interbirth intervals (IBIs). From 2006 to 2012 we studied 29 black howler (A. pigra) females living in 11 groups in Campeche (Mexico), and recorded 82 births. We recorded group size and composition and the sex of infants during weekly surveys. We calculated a food availability index based on rainfall levels and on the size of preferred food resources. Daughters had a 30 % higher probability of surviving than sons, and the survival of the latter was positively related to food availability. IBI decreased when the first infant in the interval died, and when considering only IBIs in which the first infant survived, IBIs were longer following the birth of a daughter. These results suggest that, even if the production of daughters reduces reproductive output due to longer IBIs, female black howlers may still accrue higher reproductive success through their daughters due to differences between sexes in survival.     

A bioeconomic study on a provisioned troop of Japanese monkeys (Macaca fuscata fuscata) at koshima islet,Miyazaki

The natural and provisioned (wheat) food intake of the Japanese monkeys on Koshima was measured by direct observation. It was found that the portion of wheat consumed reflects such social structures in Japanese monkeys as (a) the structure of cocentric circles composed of several classes, (b) female ranking orders, (c) social strictness in breeding or non-breeding seasons. The natural food intake forIcho (2–3 years old female) was estimated for three seasons (April, September and December) during 1971. Her daily caloric intake was estimated from a quantitative list of natural foods eaten and the quantity of wheat eaten by multiplying the appropriate caloric values, and digestibility of 70%. The kcal day per values were 411 in spring, 522 in summer and 559 in winter. Her daily energy consumption (DEC) was estimated to be 398, 423, and 447 kcal/day in the respective seasons derived from the equation DEC =153W^2/3 which was obtained from data on activity telemetry and basal metabolic rates. The two spring values are in agreement. The summer and winter values show considerable differences. The dependency on wheat was calculated for individuals of various ages and sexes. The dependency of juveniles (60%) is about double that of ordinary females (25%). The Koshima troop is largely dependent on the evergreen broad leaves through all seasons. The increase of the number of females was cumulatively simulated assuming constant age-specific fecundity and mortality. There appeared one stagnated period of increase during the years 1961–1964 due to external factors. It will be a future problem to relate the quality of nutrition to reproductive performance.     

Seasonality of births in Homo sapiens in pre-industrial Finland: maximisation of offspring survivorship?

We examined the seasonal variation in human birth and infant survival rates in pre-modern Finland. If survival probabilities of children born during different seasons of the year differ and if timing of reproduction has been affected by natural selection, periodic variation in environment could have led to reproduction during the season of best infant survival expectations. Significant seasonal variation in both birth rate and survival probability was found, but the monthly birth and survival rates of newborn were uncorrelated. Hence, if there was any tendency to maximise the reproductive success, increase in some other component of fitness than the infant survival was probably targeted. The effect of major holidays on the birth rate was proved to be notable, suggesting that although the basis for seasonal variation in birth rate was biological, sociocultural factors had an impact on the timing of reproduction in humans. The overall mortality of infant boys exceeded that of infant girls in all seasons. This difference was smallest during the time of best food supplies, indicating that the development of males was less buffered against environmental disturbances than that of females.     

It’s All in the Timing: Birth Seasonality and Infant Survival in <Emphasis Type="BoldItalic">Eulemur rubriventer</Emphasis>

Highly seasonal breeding has been considered one of the keys to understanding Malagasy primate socioecology. Strict seasonal breeding may be particularly critical for Malagasy primates because they live in such energetically challenging seasonal environments. Lemurs also live in highly unpredictable environments, and there is growing evidence that reproductive timing may be mediated by additional factors, suggesting that more relaxed breeding seasonality is adaptive in some cases. I tested the adaptive breadth of the birth peak in Eulemur rubriventer, which breed in several different months. I describe reproduction in the species by determining the timing and extent of the birth season (period in which all births occur) and birth peak (period in which the majority of births occur); test whether relaxed reproductive seasonality might increase reproductive success by comparing infant mortality within and outside the birth peak; and model the extent to which fruit availability has an influence on the timing of reproduction. I collected birth data on 5 groups in 2003–2005, which I combined with demographic data that D. Overdorff collected from 5 focal groups and additional censused groups between 1988 and 1996. Thirty births occurred in 8 different months. Births were significantly seasonal, with a unimodal birth peak in late August/September/October, and a mean birth date of October 11. Twenty-three births (76.7%) occurred within 54 d (14.79%) of the year. No births occurred May–July, indicating that conceptions did not occur from late December through late February, and cycling (estimated using gestation length) did not occur until ca. 101 d after the austral summer solstice (December 21). Of 22 infants followed regularly, 18 were born in the birth peak, of which 2 died (11%). All 4 infants born out of season died. Based on fruit availability, I calculated a Theoretical Overlap index (T), which indicated a 3-mo window with optimal food conditions for reproduction. This window corresponded to the timing and breadth of the birth peak in Eulemur rubriventer. These results indicate that a breeding season >3 mo within a given year is not adaptive in the species, likely due in large part to the availability of fruit during key reproductive stages, particularly before breeding.     

Reproduction in wild female olive baboons

The purpose of this paper is to evaluate several factors that influence female reproduction in a large troop of wild olive baboons (Papio cynocephalus anubis) based on 4 consecutive years of demographic data. Interbirth intervals were significantly shorter for females whose infants died before their next conception than for females whose infants survived. High-ranking mothers of surviving infants had significantly shorter birth intervals than comparable low-ranking mothers, independent of maternal age. This occurred mainly because the interval from resumption of cycling to conception was significantly shorter for high-vs. low-ranking females. Dominance rank did not influence sex ratio at birth, infant survival in the first 2 years, or adult female mortality. Age was also significantly related to interbirth intervals, with older females having shorter intervals. Primiparous females had consistently longer reproductive intervals than did multiparous females, but this difference reached statistical significance only for females whose infants died before the next conception. Primiparous females also experienced significantly higher infant mortality. Data on body size and estrous cycle length indicated no differences between high- and low-ranking females. Nutritional and stress-related mechanisms that may underlie the reproductive advantages of high rank are discussed.     

Life History of Cercopithecus mitis stuhlmanni in the Kakamega Forest, Kenya

Comparative data from wild populations are necessary to understand the evolution of primate life history strategies. We present demographic data from a 29-yr longitudinal study of 8 groups of individually recognized wild blue monkeys (Cercopithecus mitis stuhlmanni). We provide estimates of life history variables and a life table for females. Most females had their first infant at 7 yr. The mean interbirth interval was 28 mo, and decreased from 31 to 18 mo if the first infant died within a year. Interbirth intervals did not differ according to infant sex, but females had longer intervals after their first vs. subsequent births. Infant mortality was 23% and did not differ strongly by sex or mother’s parity. Maximal female lifespan was 32.5–34.5 yr. Across the lifespan, both survivorship and fecundity showed typical primate patterns. Survivorship was lowest in infants, leveled off among juveniles, and then decreased gradually with increasing age in later life. Fecundity was highest among young females and decreased among older females. Births were seasonal, with 64% occurring within 3 mo at the end of the dry season and beginning of the wet season. Survival to 12 mo was higher for infants born during drier months. Birth season timing is plausibly related to thermoregulation of infants, weanling foods, or maternal energy demand. Blue monkeys are a forest-dependent species with a very slow life history and relatively low immature and adult mortality rates compared to closely related guenons living in open habitats. Even among cercopithecines as a whole, they appear to have an exceptionally slow life history relative to body size. Differences in life history “speed” between blue monkeys and their close relatives seem to be related to lower juvenile and adult mortality in forests relative to more open habitats.     

Red howler monkey birth data II: Interannual,habitat, and sex comparisons

Data presented in this paper are derived from the births and subsequent histories of red howler infants born in two habitats. Overall the sex ratio of infants at birth was about 1:1. Infant survivorship (at 1 yr) was about 80%, and 44% of infant mortality was attributed to infanticide by males. Survivorship curves indicated a dramatic sex difference, with far fewer females than males known to be alive at age 7 yr. However, this sex difference may be inflated because emigrant males are more easily identified than emigrant females, and females may be dispersing beyond the boundaries of the study area at a higher rate. Annual birthrate varied somewhat from year to year and was positively related to rainfall. Annual birthrate tended to be higher in the habitat with lower density and higher growth rate. Consistent with the trends, in annual birthrate, variation in interbirth interval length (TBR after births of surviving infants was related primarily to habitat differences and annual variation in rainfall. Season of birth and maternal age class had no effect on IBI. Infant sex had mostly nonsignificant effects on IBI. A small sample indicated that IBI's were significantly longer after the births of females who eventually became natal breeders than after the births of females who eventually emigrated. This difference might reflect differential parental (maternal) investment of some sort.     

Female rank and reproductive success among arashiyama B Japanese macaques (Macaca fuscata)

Five hypotheses that related female rank and reproductive success were tested in an intact troop of free-ranging, provisioned, Japanese macaques. The hypotheses stated that high-ranking females (1) begin parturition earlier in life than low-ranking females; (2) produce more offspring than low-ranking females; (3) give birth during some optimal time during the birth season to a greater extent than low-ranking females; (4) experience less infant mortality than low-ranking females;and (5) more frequently produce male offspring, while low-ranking females more frequently produce female offspring. A statistical analysis of the data which included three birth seasons and 55 adult females and 34 pubescent females, all of known age, rank, and matrifocal membership in the Arashiyama B troop, revealed few significant results. An association was found between the rank of the matrifocal unit and the age of first birth. However, the relationship was the reverse of hypothesis 1, i.e., females of the lower-ranking matrifocal units began parturition earlier than females of higher-ranking matrifocal units. Therefore, in this troop of Japanese monkeys— where alternative feeding strategies existed— there was little association between female rank and reproductive success.     

Sources of variation in interbirth intervals among captive bonnet macaques (Macaca radiata)

Female fitness is a function of variation in the length of females' reproductive careers, the viability of their offspring, and the frequency with which they give birth. Infant loss shortens interbirth intervals in most primate species, but we know considerably less about other factors that contribute to variation in the length of interbirth intervals within groups. In one large captive group of bonnet macaques, maternal parity, age, experience, family size, and recent reproductive history are all associated with variation in the length of intervals that follow the birth of surviving infants. Primiparous females have the longest interbirth intervals, while multiparous females who have produced surviving infants in the past and have raised their last infant successfully have the shortest interbirth intervals. Infant sex and maternal rank have no direct effect upon the length of interbirth intervals. One of the underlying causes of variation in the length of interbirth intervals after surviving births seems to be variation in the timing of conceptions among females. Females who conceive early in the mating season tend to have shorter interbirth intervals than other females. However, females who are multiparous, experienced, and have recently raised infants have late conceptions and short interbirth intervals.