Reproductive Strategies of <Emphasis Type="Italic">Trachypithecus pileatus</Emphasis> in Arunachal Pradesh,India

We studied reproductive behavior of free-ranging capped langurs (Trachypithecus pileatus) in the Pakhui Wildlife Sanctuary, Arunachal Pradesh, India. Four species of primates —Trachypithecus pileatus, Macaca mulatta, M. assamensis, and Nycticebus bengalensis— live there. We studied the mating seasons, mating frequency, copulatory attempts, time spent in copulation, and interval between 2 successive copulations, gestation length, and interbirth interval of 4 groups of capped langurs during 2001–2003. We observed 2 mating seasons in a year. The first was larger, comprising 5 months (September–January), and the second was short, April and May. Mating was intensive in the morning session (0600–1000 h); 57% of total mating events occurred then. The average gestation period was 200 d. November was the most favorable month for breeding. In a year, 107 mating events occurred involving 5 adult females. Average time per mounting attempt is 12 s. Duration of mounting was the maximum in November. Interbirth interval was 23 months and 10 d. The birth season was 129 days, December–April; 53% of births occurred in February and March. Average birth rate is 0.386 birth/female/yr.     

The social organization of forest hanuman langurs(Presbytis entellus)

The social organization of hanuman langurs (Presbytis entellus;Colobinae) was studied in Kanha Tiger Reserve, Central Indian Highlands, for 2300 hr (1980–1985), in a mosaic of moist deciduous forest and anthropogenic meadow. The langur population density was 46.15/km ² and the mean troop and band sizes were 21.7 and 14.0, respectively. Of 14 troops, 13 were one-male and 1 was trimale. The population adult sex ratio was 1:2.5. The majority of female sexual solicitations was directed toward the harem male. The birth season was December to May, with an estimated gestation of 171–224 days. A review of langur reproductive seasonality suggests that breeding throughout the year is confined to those populations able to exploit human food sources. Mortality during the first year of life was 40%, including infanticide. A significant positive correlation was found between the age of an infant at death or disappearance and the mother’s subsequent interbirth interval. Five cases of social change are described, including female transfer, one-male to multimale change, troop formation, and gradual and rapid replacement of troop males. Takeover-associated infant killing by band males, in an undisturbed moderate-density population, supported the sexual-selection/infanticide hypothesis but not the social-pathology hypothesis. However, it could not be directly confirmed that an invading infanticidal male gains a reproductive advantage. The male tenure of harems was estimated to be 45 months.     

Life history of yellow baboons: Physical development,reproductive parameters,and infant mortality

Longitudinal data from a population of yellow baboons,Papio cynocephalus, in the Amboseli National Park, Kenya, provide life history parameter estimates. Females reached menarche at approximately four-and-a-half years of age and then cycled for approximately a year before first conception. Postpartum anestrum averaged 12 months but ranged from six to 16 months. In cases of still births or infant death during postpartum amenorrhea, females commenced cycling after approximately one month. In mature females the time spent cycling before conception was five months on the average with a range from one to over 18 months. Only half of all full-term pregnancies resulted in infants who survived the first year of life; only a third, in infants who survived until the birth of their mother’s next infant. In comparison with data from laboratory colonies, our data indicate that female baboons in Amboseli are older at birth of first infant. They have, on the average, a somewhat shorter interbirth interval than was estimated from earlier crossectional field data, and therefore spend a larger portion of their adult life pregnant, but have a much longer interval—at least three years on the average—between the birth of an infant and the birth of that infant’s next older surviving sibling. A number of morphological changes in immature baboons are described.     

A ten-year summary of reproductive parameters for ring-tailed lemurs at berenty, madagascar

From 1989 to 1998, 204 live births were recorded for ring-tailed lemurs (Lemur catta) at Berenty, Madagascar. Excluding unknown birth dates, the peak month of birth was September, with 82.0% (146/178) occurring during this period. The offspring sex ratio (1∶1.19) was not significantly different from 1∶1, and there was no association with the mother's age. The first births occurred at the ages of 2 to 4 yr. The annual birth rate was very low at the age of 2 yr (11.1%), but increased thereafter: to 50.0% at the age of 3 yr, and to 75–85% at the age of 4 or more years. Multiple births were very rare, since only three sets of twins and one set of triplets were recorded. As for the interbirth interval, a one-year interval was the most common (92.2%). Infant mortality within the first year was 37.7% (77/204). Neonatal mortality within the first month accounted for 31.2% of all infant dealths.     

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.     

Birth spacing in langur monkeys (Presbytis entellus)

This paper presents 10 years of reproductive data on birth interval length and 5 years of data on reproductive behavior postpartum from a captive colony of gray langur monkeys (Presbytis entellus)housed in Berkeley, California. Birth intervals of females following different pregnancy and nursing schedules are compared. Females whose infants survive to the age of 9 months have a median birth interval of 15.4 months. The experimental separation of mothers from infants for a period of 2 weeks, 6 to 9 months postpartum, had no significant effect on the median birth interval length. Females experiencing a pregnancy failure or the loss of a neonate had median birth intervals of 9.6 and 10.7 months, respectively. These intervals were significantly shorter than the birth intervals of females whose infants survived to 9 months, showing that the presence of a nursing infant delays the female’s time to next conception by approximately 5 to 6 months. Females experienced a median of three estrous periods (two estrous cycles) before conceiving postpartum, regardless of pregnancy outcome or length of infant survival, and females rarely conceived during their first estrous period postpartum. Weaning did not occur until after the mother’s next conception. These data indicate that, in populations of langurs characterized by average birth intervals of 15 to 16 months, the loss of an infant after the age of 5 to 6 months will not accelerate a female’s ability to conceive or shorten the birth interval length. The available data on birth spacing from populations of free-ranging langurs are reviewed. It could not be demonstrated that non-Himalayan populations are characterized by birth intervals which are as long as 20 to 24 months. Rather, it is suggested that female langurs inhabiting seasonally arid sites, such as Jodhpur, Abu, and Dharwar, may be capable of producing infants on the average of every 15 to 16 months. Flexibility in the timing of births and the lack of well-defined birth seasons at these sites may be explained by this species’ dietary and digestive adaptations. Additionally, data on birth spacing and the age of missing infants from the above field sites, where it has been suggested that infanticide following changes in male leadership occurs habitually, do not lend support to the sexual selection hypothesis of infanticide as proposed by S. Hrdy (1974, 1977).     

Birth intervals ofCercopithecus monkeys of the kakamega forest,Kenya

Data on interbirth intervals are reported for two forest-living guenons,Cercopithecus mitis andC. ascanius, from a western Kenyan site. Measured intervals for females whose first offspring survived varied from 24 to 54 months (median 47,N=10) forC. mitis, and from 49 to 60 months (median 52,N=3) forC. ascanius. Intervals were shorter when the first of two offspring died. These results are supported by data on estimated intervals, in which the date of the first of two births was estimated, and incomplete intervals. Our measurements exceed previous estimates of interbirth intervals in wild populations and measured intervals of captive animals. Compared to closely related species inhabiting unpredictable and seasonal environments, these forest guenons breed very slowly indeed.     

Determinants of fecundity and reproductive success in captive vervet monkeys

Between 1975 and 1983, adult female vervet monkeys (Cercopithecus aethiops sabaeus) over 3.5 years of age, living in two undisturbed social groups in a captive colony in Sepulveda, California, have averaged 1.0 births per female year with a mean interbirth interval of 10.7 months. Increased fecundity did not result in decreased survival rates of offspring in this population. Fecundity was influenced by the mother's age and dominance rank. The primary factor in the age-fecundity relationship was the age at first birth, which varied from three to five years. High-ranking females contributed the most to the high rate of fecundity, with significantly shorter interbirth intervals, more births per female year, and more surviving infants compared to low-ranking females.     

Birth seasonality and interbirth intervals in free-ranging formosan macaques,Macaca cyclopis, at Mt. Longevity, Taiwan

Thebirth season of Formosan macaqueM. cyclopis during our study started in February and ended in August with a peak in the second half of April and the first half of May. The average birth rate was 82%±21 for 114 females with four years of breeding records. Our study reports that a time span of one year between births can be considered as the norm for the wildM. cyclopis. Of the 288 inter-birth intervals (IBI), 88.5% showed a 1-year interval (mean 364±SD 29 days); 11% showed 2-year interval (727±36 days); and 1% (2 females) had 3-year interval (range 1030–1040 days). The IBI for females that had infant loss within six months of life were the shortest. But there was no significant difference from that of females that had stillbirth (p>0.9) and infant that survived for first six months of life (p>0.06). However, among 255 cases of 1-year IBI, stillbirth or following infant loss within six months of life did significantly shorten IBI for ten days (F _1,253=5.74,p<0.05).     

Life-history characteristics of a wild population of vervets (Cercopithecus aethiops sabaeus) in Barbados,West Indies

Life history data are presented for a population of vervets, Cercopithecusaethiops sabaeus, in Barbados, West Indies. The data were obtained from two habituated troops and from vervets captured during a large-scale trapping program. Individuals of known age from one troop were weighed periodically, and separate growth curves generated for males and females. The mean weight of captured adult females was 3.3 kg; that of adult males, 5.3 kg. The average age at sexual maturity is estimated at 34 months for females and 60 months for males. Vervets give birth throughout the year, but most infants are born between April and July. The average interbirth interval following a surviving infant is 11.8 months. The mortality of juveniles is heaviest between birth and 2 years of age and decreases thereafter. Males emigrate from their natal troops at sexual maturity and one incident of a juvenile female emigrating is reported.     

Timing of births in sympatric brown howler monkeys (Alouatta fusca clamitans) and northern muriquis (Brachyteles arachnoides hypoxanthus).

We monitored the birth patterns of sympatric brown howler monkeys (Alouatta fusca clamitans) and northern muriquis (Brachyteles arachnoides hypoxanthus) during a 4‐yr period from October 1996 to August 2000 at the Estação Biológica de Caratinga, Minas Gerais, Brazil. Brown howler monkey births (n = 34) occurred throughout the year, and birth frequencies did not differ between rainy and dry season months. The aseasonal birth patterns of the howler monkeys differed significantly from the dry season concentration and dry month peak in muriqui births (n = 23). We found no effects of infant sex or the number of females on interbirth intervals (IBIs) in our 10 howler monkey study troops. IBIs of brown howler monkeys averaged 21.2 ± 2.5 mo (n = 8, median = 21.0 mo), and were significantly shorter following dry season births than rainy season births. Their IBIs and yearling survivorship (74%) were similar to those reported for other species of howler monkeys, but yearling survivorship was much lower than that of muriquis (94%), whose IBIs were more than 12 mo longer than those of the howler monkeys. Our study extends comparative knowledge of birth patterns in Alouatta to a poorly known species, and provides insights into the different ways in which diet and life history may affect the timing of births in large‐bodied platyrrhines under the same seasonal ecological conditions. Am. J. Primatol. 55:87–100, 2001. © 2001 Wiley‐Liss, Inc.     

Male reproductive success in harem troops of hanuman langurs (Presbytis entellus)

Based on cross-sectional and longitudinal data collected in 1967–1988 by various observers, male reproductive success was studied in the Hanuman langurs of Jodhpur, India. The harem-structured social organization ensures a high degree of paternity certainty. Births occur throughout the year, with significant peaks and minima in March and November, respectively (n =398).The interbirth interval averages 16.7 months (n = 114).The duration of harem residencies varies between 3 days and ≥ 74.0 months, with a mean of 26.5 (n = 64). Harem holder replacements occur during all months of the year. No male achieves residency in more than one troop, suggesting that residency is associated with a distinct peak in the resource holding potential of a given male. Reproductive success among males varies considerably. Male mortality is high due to migration and intrasexual competition, leading to an adult sex ratio of 1:4.9. It is estimated that one-quarter of all adult males will never gain harem residency. Conceptions achieved outside harem residencies are so rare (4.7%) that a viable low-risk strategy, opting for longevity instead of harem residency, is unlikely. Tenure length has a stronger influence on male reproductive success than harem size because interbirth intervals are significantly shorter in small harems than in larger ones. It is assumed that females in one-male breeding structures compete for sperm and that such competition is more intense in larger harems.     

Marriage season, promptness of successful pregnancy and first-born sex ratio in a historical natural fertility population – evidence for sex-dependent early pregnancy loss?

 We investigated population-based vital records of the seventeenth and eighteenth century French Canadian population to assess the effects of marriage season on the outcome of the first births under natural fertility conditions (n=21,698 marriages). Promptness of the first successful conception after marriage differed according to marriage season; the proportion of marriages with a marriage-first birth interval of 8.0–10.0 months was lowest (34%) for marriages in August–October (P=0.001). Although the male/female sex ratio of the babies born with an interval of 8.0–10.0 months was generally higher (1.10) than those with an interval of 10.0–24.0 months (1.05), the marriages in August–October resulted in a significantly reduced sex ratio (0.96) among only the prompt conceptions (P=0.026). We discuss whether this seasonal reduction of the sex ratio could be partly explained by a clustered pregnancy loss of male zygotes in early pregnancy. Received: 5 January 1998 / Accepted: 9 September 1998     

Mother-infant relationships in Vervet Monkeys: Response to new adult males

The reaction of mothers to replacement of breeding adult males was studied in two captive groups of vervet monkeys. Mother-infant behavior for 15 infants born in the season following the introduction of new males was compared to mother-infant behavior for 35 infants born with adult males that had been resident in the group for more than a year. The mothers responded to the presence of new males by being more protective toward their infants in the first 3 months. Increased protectiveness disappeared in the second 3 months, and in the infant’s sixth month of life mothers with new males in the group became more rejecting than mothers with long-term resident males. The combination of increased protectiveness and increased rejection was unusual among the mothers with long-term resident males but was the most common mothering style used in the presence of new males. The rate of rejection was inversely correlated with the interbirth interval, and mothers with new males in the group conceived sooner and had significantly shorter inter-birth intervals compared to mothers with long-term resident males.     

Longitudinal patterns of reproduction in wild female siamang (Hylobates syndactylus) and white-handed gibbons (Hylobates lar)

I present the 6- year reproductive histories of three wild female siamang (Hylobates syndactylus)and four white-handed gibbons (Hylobates lar)at the Ketambe Research Station (Sumatra, Indonesia). Reproductive output varied considerably among females. Two females failed to gestate: both were nulliparous young adult H. lar,one of which remained unpaired for 4 years after dispersing from her group, while the other lost her recently acquired mate to another female. Only one- (a white-handed gibbon)- gave birth more than once, yielding interbirth intervals of 22 and 31 months. Pair bond stability or reduced interspecific feeding competition or both factors may have contributed to the brevity of these intervals. The other females- one H. lar,and three H. syndactylus-each gave birth once, suggesting minimum interbirth intervals exceeding 4–5 years (H. lar)and 3 years (H. syndactylus)in these individuals. Even given the pronounced variation observed among H. lar,these data suggest that interbirth intervals may often exceed the 2- to 3- year interval commonly attributed to these two species. Sources of reproductive failure were 1) maternal abandonment of the neonate due to impaired ability to provide maternal care (H. syndactylus,),(2) premature or stillbirth (H. syndactylus,),and (3) pregnancy termination (H. lar).These data and a review of information on longevity and age at menarche suggest that the actual lifetime reproductive output of a siamang or white-handed gibbon female may often fall far short of the 10 offspring/lifetime originally proposed for these species. Indeed, females may rear as few as five offspring to weaning in a lifetime, which is a figure reminiscent of the reproductive potential of some pongids. Finally, variance in female reproductive success is higher than expected in these monogamous species, which suggests that females (and males) are under strong selective pressure to exert mate choice, possibly through acquisition of (new) mates and extrapair copulations. Future research must clarify the availability of opportunities for paired adults to engage in these sociosexual behaviors.     

Interbirth interval variation in three sympatric species of neotropical monkey

Relatively few papers have focused on interbirth intervals in primates, even though the spacing between births is one of the primary determinants of female reproductive success in long-lived mammals. We present life history data from a ten-year field study of Costa Rican capuchins (Cebus capucinus), howlers (Alouatta palliata), and spidei monkeys (Ateles geoffroyi). Analyses of intraspecific variability found no significant differences attributable to individual variation in age, parity, weight, or maternal rank. Loss of an infant significantly shortened the interbirth interval in all three species. There was no correlation between annual rainfall and birth rates, but there was a significant clustering of births in the dry season. Survival analyses demonstrated a significant difference between the median interbirth intervals of the three species. Howlers have the shortest intervals (19.9 months), capuchins exhibit longer intervals (26.36 months), and spider monkeys have the longest intervals (34.72 months;. This comparative pattern does not correspond to relative body weights of the three species, but does correspond to relative brain weights. Comparisons to other primates with similar life history characteristics demonstrate that interbirth intervals are best examined at the level of their three component phases: gestation, lactation, and cycling to re-conception. © 1995 Wiley-Liss, Inc.     

Population dynamics of wild chimpanzees at Bossou,Guinea, between 1976 and 1983

The population dynamics of a small group of wild chimpanzees at Bossou, Guinea, were studied during a 6.5-year period between 1976 and 1983. The natality rate (0.23 births/female/year) was higher and the interbirth interval (4.3–4.4 years/female) was shorter than those of chimpanzees at East African study sites (the Gombe and Mahale National Parks). The infant mortality for the first 3 years (0.06–0.18/year) was lower than those in East Africa. However, the population had remained almost stable since 1967 (growth rate: 0.985/year). The increase in number by births was offset by the disappearance (perhaps emigration) of adolescent chimpanzees. Adult males immigrated and disappeared (perhaps emigrated) but adult females rarely did.     

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.     

Troop history,female reproductive strategies and timing of male change in Hanuman langurs,Presbytis entellus

Female reproductive data are presented from 9 years of longitudinal observations on two troops of Hanuman langurs (Presbytis entellus) living around Jodhpur, India. On the basis of 89 live births interbirth intervals were calculated to examine the effect of demographic factors on reproductive behaviour and troop composition. Sex of an infant seems to influence the length of intervals which are longer after the birth of female infants at an average of 1.7 months. It is suggested that this may be an outcome of differential maternal investment by allocating more time and energy towards female infants who run a higher mortality risk than male infants, at least up to an age of 27 months. Troopspecific interbirth intervals are influenced by social events. If the last infant is still alive when the next one is conceived, the intervals are significantly longer than after the premature loss of an infant (Bijolai troop: 15.6 vs. 12.1 months; Kailana-1 troop: 16.7 vs. 11.4 months). During undisturbed male tenureship intervals are shorter than after a male change (Bijolai troop: 14.3 vs. 16.0 months; Kailana-I troop: 15.6 vs. 17.5 months). Thus the frequency of male changes can influence the demography of a troop. Furthermore, the data suggest that take-overs are optimally timed by males. New males tend to take over a troop when most of the females are cycling.     

Demography and life history of free-rangingPropithecus diadema edwardsi in ranomafana national park,madagascar

I conducted the first long- term study of the life history patterns of Propithecus diadema edwardsi—Milne- Edward’s sifaka— in the rain forests of southeastern Madagascar, beginning in 1986. I report behavioral observations on a total of 33 individuals from three groups over a 9- year span. We captured,marked, and released 21 individuals. Individual group size ranged from three to nine sifakas. Two breeding females lived in groups I and II until 1993. A newly formed group (III) had one breeding female. Age at first reproduction is 4 years for females and 5 years for males. Gestation length is 179 days (n =2). Most births occurred in June (n = 17), but infants were also born in May (n = 2) and July (n =2). Nine of 21 (43%) infants born died before the age of 1 year, and 15 (67%) died before the age of reproduction. One female bred in her natal group after the death of the resident male and the immigration of an adult male. Another two females disappeared at 4 and 5 years of age;they could have emigrated or died. All 5- to- 6- year- old males (n = 4) have emigrated from their natal groups to adjacent groups. Two have committed infanticide. Five or more individuals were killed by Cryptoprocta ferox.Despite high mortality and offspring dispersal, the number of individuals in the two main groups remained nearly the same over the 9- year study.