Hormonal changes during the mating and conception seasons of wild northern muriquis (Brachyteles arachnoides hypoxanthus)

We investigated hormonal and behavioral changes in wild male and female northern muriquis (Brachyteles arachnoides hypoxanthus) at the Estação Biológica de Caratinga, Minas Gerais, Brazil, during a 6‐mo period that encompassed the onset of the 1998–1999 mating and conception seasons. Individual females resumed mating with the resumption of ovarian cycling, which was not synchronized among them or related to their cortisol levels. Females experienced two to seven cycles prior to conceiving, and the first conception occurred 2 mo after the onset of the group's mating season. There were no differences in female cortisol levels across their premating, mating, and conception conditions. Cortisol levels were significantly higher in females than in males prior to the conception season, consistent with the prediction that energy reserves may be associated with breeding readiness in females, but not males, in this species. The sustained elevation in male cortisol occurred after the peak in their sexual activity, which resulted in the first conception of the year. Male cortisol levels were positively correlated between years that were similar in rainfall, but differed in the timing of sexual and reproductive events. The timing of cortisol elevations in males appears to be generally regulated by environmental cues, but is responsive to fine‐tuning by social and behavioral cues related to the unpredictable timing of reproductive opportunities within their extended mating season. Am. J. Primatol. 61:85–99, 2003. © 2003 Wiley‐Liss, Inc.     

Behavioral indices of estrus in a group of captive African elephants (Loxodonta africana)

This study investigated behavioral signals of estrus by systematically monitoring the interactions of one male with four female African elephants housed in a naturalistic outdoor enclosure at Disney's Animal Kingdom over a period of 11 months. We measured changes in five spatial behaviors and 22 tactile‐contact behaviors, as well as changes in serum progestagen and LH concentrations, across three ovarian cycles for each female. Two females did not cycle during the study. Three different phases of the ovarian cycle were identified: mid luteal, anovulatory follicular, ovulatory follicular. The male followed more and carried out more genital inspections, flehmen, and trunk‐to‐mouth behaviors toward cycling females during their ovulatory phase. Genital inspections by the male peaked above baseline levels on the day of an LH surge, and up to 9 days before, in both cycling females and, thus, might be a useful behavioral index of estrus. The male also carried out more genital inspections, flehmen, and trunk touches to the back leg toward ovulatory cycling than noncycling females. Overall, our results indicated that: 1) a single subadult African elephant male could discriminate two females in the ovulatory phase of their cycle (i.e., during the 3 weeks preceding ovulation) from the mid luteal phase; 2) the male also discriminated two cycling females in the ovulatory and anovulatory follicular phases from two noncycling females; 3) two females in the ovulatory phase of the cycle displayed a greater variety of tactile‐contact behavior toward the male compared to the other cycle phases. Zoo Biol 0:1–19, 2005. © 2005 Wiley‐Liss, Inc.     

Reproductive endocrinology of wild female chimpanzees (Pan troglodytes schweinfurthii): methodological considerations and the role of hormones in sex and conception

Fecal and urine samples were collected from 81 female East African chimpanzees (Pan troglodytes schweinfurthii) in three major study populations in Gombe National Park, Tanzania, and Budongo Forest Reserve and Kibale National Park, Uganda. In this study I evaluated issues related to sample storage and assay reliability, and used these methods to investigate the significance of ovarian hormone levels in terms of conception success and sexual behavior. Drying of feces proved to be an effective technique and resulted in hormonal concentrations that were significantly correlated with concentrations in frozen feces. Estimates of ovarian steroid production based on urine and fecal sampling were significantly correlated with each other. The ovarian cycle profiles obtained, which were aligned relative to sexual swelling detumescence, corroborate previous findings in wild west African chimpanzees [Deschner et al., Animal Behaviour 66:551-560, 2003] in suggesting that the fertile period is limited to the last week of tumescence, but that ovulatory timing is not as precise as previously thought. A comparison across cycles confirmed the hypothesis that higher ovarian steroid levels are associated with an increased probability of conception. Females that did conceive with relatively low hormone levels had poor reproductive outcomes. Sexual behavior was tied to the probability of conception both within and across cycles. Copulatory activity within cycles closely followed the estrogen profile and was timed to coincide, on average, with the peak fertile period of females. Further, rates of copulation were significantly higher during the fertile periods of cycles that led to conception than those that did not.     

Behavioral and endocrine characteristics of the reproductive cycle in wild muriqui monkeys,Brachyteles arachnoides

The analysis of fecal ovarian steroids provides a powerful noninvasive method to obtain insights into ovulatory cycles, gestation length, and the timing of sexual interactions relative to the periovulatory period in wild primates. Techniques developed to collect and assay feces from free-ranging muriqui monkeys (Brachyteles arachnoides) for estradiol and progesterone yield the first explicit reproductive data on this species, and provide the first opportunity to evaluate the timing of observed copulations with muriqui ovarian cycles. Hormonal profiles from seven females indicate average cycle lengths of 21.0 ± 5.4 days (n=20). Females conceived after 3–6 ovulatory cycles. Gestation length averaged 216.4 ± 1.5 days for the five females for which conception cycles were sampled. Discrete copulation periods spanned an average of 2.1 ± 1.2 days (n=29), with intervals between these concentrated periods of copulations averaging 15.6 ± 6.7 days (n=20). There were no significant differences among females in cycle lengths, copulation period lengths, or copulation interval lengths. Ejaculation was visible following 71.8 ± 26.7% of copulations during the females' preovulatory periods. All females copulated outside the periovulatory period. The proportion of copulation days outside the periovulatory period was slightly greater (p=0.08) for primiparous females (64.8 ± 28.3%) than for multiparous females (28.7 ± 19.7%). Am. J. Primatol. 42:299–310, 1997. © 1997 Wiley-Liss, Inc.     

Male dominance rank and reproductive success in an enclosed group of Japanese macaques: with special reference to post-conception mating

The mating behaviour and reproductive success of male Japanese macaques (Macaca fuscata) were studied in relation to the female sexual cycles, which were monitored from the plasma profiles of gonadotropins and ovarian hormones. Based on observations of the mating behaviour during four successive mating seasons and paternity identification by DNA fingerprinting in 35 out of 37 offspring born in the subsequent birth seasons, the correlations between (1) male dominance rank and timing of mating, and (2) male dominance rank and reproductive success were examined. The results may be summarized as follows. (1) The number of copulations with ejaculation by any male was positively correlated with the male dominance rank, but not with the identified numbers of offspring fathered by each male. (2) Males could not choose ovulatory females as mating partners: the number of copulations with ejaculation with females during ovulatory weeks was not related to the male's rank. Monopolized copulations in consortship were mostly observed between high-ranking males and non-lactating parous females after conception. (3) Paternity testing showed that the male copulating most frequently with a female was not the identified father in 11 out of 15 cases. Prediction of the fathers of offspring was difficult even from the number of copulations occurring at around the estimated time of ovulation. An adaptive explanation of these correlations is discussed.     

Ecology, nutrition, and timing of reproductive events in an Asian primate, the Hanuman langur (Presbytis entellus)

Ecological conditions, feeding and ranging behaviour as well as physical condition of female Hanuman langurs ( Presbytis entellus ) were studied in order to analyse the major influences on the timing of reproductive events. The langurs inhabited a semi-evergreen forest dominated by Sal trees ( Skorea robusta ). The climate was dominated by the summer monsoon lasting from May to September. Availability of plant phytophases was markedly seasonal, with fruiting as well as flushing of the six main food plants during the monsoon. Feeding and ranging behaviour of the females varied with food availability and its distribution. High dietary quality was only obtained during a short period from May to July. Physical condition of the females varied in accordance with dietary quality and energy expenditure, with a good physical condition during the second half of the year. Births occurred from January until June, with most births around the energetically worst period of the year. The results indicate that, in contrast to several other non-human primates, most females of this population gave birth too early to meet the optimum lactation requirements. Complete weaning mainly took place during an energetically bad time of the year (October to December). However, it can be inferred that the reduction of suckling bouts prior to the next conception took place when high quality food was available. Conceptions were confined to the months of July to November, coinciding with the time of best physical condition. Moreover, females who conceived were in a better physical condition than those who failed to conceive, suggesting a primary influence of nutrition on the probability of conception. Seasonality and timing of births may be the result of a regular seasonal shortfall of resources influencing the ability of the females to ovulate and to conceive.     

Impact of social environment on female chimpanzee reproductive cycles

The socio-sexual environment of a female is known to affect ovarian function. Increased male contact can enhance menstrual cycle regularity. Conversely, social deprivation constitutes a form of stress that often alters cyclicity and the secretion of reproductive hormones. The present study was carried out on captive female chimpanzees to examine possible interactions among housing conditions, menstrual cycle length, morphological changes in secondary sexual character expression and endocrine release patterns related to follicular and luteal function. Animals were housed over a period of 2 years either with a male conspecific or singly. Blood samples were collected over three cycles, and anogenital swelling changes registered to define menstrual cycle phases. Fecal sampling techniques were used to monitor cortisol as a measure of stress-load. Male presence seemed to affect female cyclicity. Females housed with a male had shorter and more regular cycles than singly housed females. Prolactin, gonadotropins and estradiol levels were generally higher in paired females during specific cycle phases. Group variation was not always significant. No differences were found in progesterone. Sexually cohabited females tended to have lower fecal cortisol metabolites immediately before and after maximum tumescence. We suggest that the close behavioral, physical and olfactory contact with a male conspecific can act as a sort of zeitgeber to modulate ovarian function by stabilizing the female cycle and, perhaps, enhancing folliculogenesis and ovulation.     

The endocrinology of puberty and reproductive functioning in female cotton-top tamarins (Saguinus oedipus) under varying social conditions

Sexual maturation and fertility were assessed in fourteen cotton-top tamarin (Saguinus oedipus) females under various social conditions. Six tamarin females (20-28 mo of age) showed a suppression of fertility while living with their families. Hormonal profiles demonstrated low, acyclic levels of urinary luteinizing hormone (LH) and estrone-conjugates (E1C). A rapid onset of ovarian and pituitary cyclicity occurred when four of the six females were removed from their families and paired with an unrelated male. In one female, an ovulatory LH peak occurred as early as eight days after pairing and resulted in conception and full-term pregnancy. Two of the six females were housed in total isolation for 30 days following their removal from the family and prior to pairing. Gradual increases in hormone concentrations occurred during isolation; however, there was no ovarian cyclicity until each female was paired with an unrelated male. In all six females, conception occurred before or as a result of the third ovulatory cycle. Partial isolation of a 36-mo-old female resulted in elevated LH and E1C levels, but cyclicity was not observed until the female was paired with an unrelated male. These findings indicate that removal of a female from the family alone does not initiate ovarian cycling. Sexual maturation, or puberty, occurs in female tamarins living with their families between 15 and 17 mo of age when mean LH and E1C levels began to increase. However, when a female is removed and paired at 9 mo of age with an unrelated male, elevated levels of LH and E1C may be seen by 10 and 11 mo of age. Our findings indicate that a suppression of fertility occurs in cotton-top tamarins living with their families, but that reproductive suppression does not affect the process of sexual maturation. Both removal from the family environment and stimulation by an unrelated male tamarin were necessary to induce normal reproductive activity. An acceleration of puberty occurred when a female tamarin was removed from her family early in development and paired with a male.     

Reproductive Behavior in the Rhesus Monkey: Social and Endocrine Variables

SYNOPSIS. Social groups of rhesus monkeys (Macaca mulatto) livingin outdoor environments exhibit a distinct seasonal mating patternand female rhesus are observed to be sexually receptive fordiscrete periods averaging about 9 days duration. In the laboratoryenvironment mating occurs throughout the year and, in the pairtest, female rhesus are observedto be sexually receptive throughall phases of a menstrual cycle, with a periovulatory peak incopulatorybehavior. The apparent conflict between results from field andlaboratory studies has been difficult to resolve because ofmethodological limitations inherent in each study environment.Studies conducted on social groups of rhesus monkeys housedin outdoor compounds, an environment in which the species typicalseasonal mating pattern is preserved and which allowsfor concomitantmeasurement of behavioral and hormonal variables, provided informationabout the covariance between female sexual behavior and ovariancycles. Female copulations were observed only in associationwith ovulatory cycles, and were limited to the follicular andperi-ovulatory phases of such cycles, demonstrating that copulatorybehavior in female rhesus monkeys is strongly influenced bycyclic hormonal variables. The studies also revealed that femalestend to conceive on the first ovulatory cycle of the season,that there was no synchrony of cycles among the females, andthat the best predictor of the timing of ovulation in a particularfemale is reproductive outcome in the previous year.     

Patterns of anogenital swelling size and their endocrine correlates during ovulatory cycles and early pregnancy in free-ranging barbary macaques (Macaca sylvanus) of Gibraltar

In macaques and other cercopithecoid primates, large anogenital swellings (AS) are generally found only in those species in which reproduction is not seasonally restricted. In this respect, the Barbary macaque is unusual because while it shows a marked degree of reproductive seasonality, it also exhibits a striking, exaggerated swelling of the circumanal region and labia. Information on the characteristics of AS in female Barbary macaques is limited in that it is largely based on semiquantitative assessments of swelling size, and there are no data on endocrine parameters associated with AS during ovulatory cycles or early pregnancy. In the present study, we combined quantitative measurements of four swelling size parameters (AS width, height, and depth, and labial width) using a video-imaging technique with fecal estrogen and progestagen determinations in free-ranging females of the Gibraltar Barbary macaque population to 1) characterize the pattern of AS throughout the mating season and early gestation, and 2) examine the relationships among changes in swelling size and endocrine parameters. The patterns of all four swelling parameters correlated significantly with one another, although measures of AS depth and labial width were difficult to obtain. Using the product of AS height and width, the data demonstrate that the occurrence of AS is highly seasonal, with pronounced cyclical changes during the mating season and early pregnancy. Furthermore, the swelling cycles are characterized by progressive size increases from the early to the late follicular phase, in association with an elevated estrogen:progestagen (E:P) ratio, with ovulation occurring during the maximum swelling phase. The results also demonstrated a conspicuous postconception increase in swelling between days 18-30 of gestation. The postconception swellings were on average 80% of the size of that of the conception cycles, and were preceded by a large increase in fecal estrogen levels and the E:P ratio. This is the first study to characterize swelling patterns and their endocrine correlates during ovarian cycles and early pregnancy in naturally reproducing female Barbary macaques. The data provide a solid basis for further studies to explore sociosexual behavioral patterns and the functional significance of AS in this species.     

Isolation accelerates reproductive senescence and alters its predictors in female rats

The process of reproductive senescence in female rats (Rattus norvegicus, Sprague-Dawley strain) was altered by their social environment during adulthood. The incidence of constant estrus (CE), which marks the end of estrous cyclicity, was nearly twice as high in females living in isolation as it was in females living in groups. Isolated females also entered CE at three times the rate of group-housed females. In addition, the characteristics of a rat's estrous cycle when she was young predicted whether or not she would enter CE during reproductive senescence. However, the characteristics of the cycle that predicted if a rat would enter CE were different for isolated females than for females living in groups. In isolated rats, entry into CE was predicted by a pattern of regular cycles followed by irregular cycles, a lordosis reflex of consistently high intensity during irregular cycles, and an absence of spontaneous pseudopregnancies. Furthermore, a long duration of CE was predicted by early cessation of estrous cycles. In rats living in groups, increased estrogenization of the vaginal smears during irregular cycles was the only predictor of entry into CE. In both environments, the onset of an acyclic lordosis reflex predicted the timing of CE. The potential role of ovarian steroids as mediators of these effects is discussed.     

Characterization of the estrous cycle in Octodon degus

We characterized the reproductive cycle of Octodon degus to determine whether reproductive maturation is spontaneous in juveniles and if ovarian cyclicity and luteal function are spontaneous in adults. Laboratory-reared prepubertal and adult females were monitored for vaginal patency and increased wheel-running. Sexual receptivity was assessed by pairing adult females with a male 1) continuously, 2) at the time of vaginal patency, or 3) following estradiol treatment. Blood samples were assayed for estradiol and progesterone concentrations on Days 1, 4, 8, and 16 relative to vaginal opening. Ovarian tissues were collected 6 and 16 days after behavioral estrus and 6 days after copulation for histology. In juveniles, the onset of cyclic vaginal patency and increased wheel-running activity was spontaneous, occurred in the absence of proximal male cues, and appeared at regular intervals (17.5 ± 1.4 days). In adults, vaginal patency and increased wheel-running occurred cyclically (21.2 ± 0.6 days) in the absence of proximal male cues, and these traits predicted the time of sexual receptivity. Corpora lutea develop spontaneously and are maintained for 12-14 days. The ovaries had well-developed corpora lutea 6 days after mating and 6 days after estrus without mating. Progesterone concentrations were highest in the second half of the cycle when corpora lutea were present and estradiol concentrations peaked on the day of estrus. Thus, female degus appear to exhibit a spontaneous reproductive cycle consistent with other Hystricognathi rodents. Octodon degus is a novel model with which to examine the mechanisms underlying different reproductive cycles.     

Female sexual swelling size, timing of ovulation, and male behavior in wild West African chimpanzees

Conspicuous swellings of the perineal skin can be observed in females of many catharrine primate species particularly during the middle stages of the ovarian cycle. The functional significance of this trait remains poorly understood. Recently, two hypotheses, the "reliable indicator" hypothesis and the "graded signal" hypothesis that take into account not only the pattern but also the exaggerated size of sexual swellings, have gained attention. Here we test several predictions made by these hypotheses by combining (i) direct size measures (from video captures) of female sexual swellings with (ii) urinary hormone data to indicate timing of ovulation through enzyme immunoassay measurements of estrone conjugates and pregnanediol glucuronide (PdG) and (iii) behavioral observations of male mating efforts throughout 36 ovulatory cycles in 12 wild chimpanzees. We are able to show that (i) even within the traditionally defined maximum swelling period, further slight increases in swelling size indicate approaching ovulation, and (ii) that male mating interest changes according to the changes in swelling size. Furthermore, absolute swelling size during the periovulatory period increases and the alpha male associates more with females as the number of cycles to conception decreases. Finally, when having the choice between several "maximally" tumescent females, the alpha male prefers the female that is in the fertile phase of her cycle rather than that with the biggest swelling at that time. Thus, most of our findings are in line with the predictions of the graded signal hypothesis while none of them would support the reliable indicator hypothesis.     

Reproduction in free-ranging Propithecus verreauxi: Estrus and the relationship between multiple partner matings and fertilization

Female sifaka mate selectively with one or more resident and/or non-resident males during the breeding season. Various adaptive explanations have been advanced to explain why female primates mate with multiple males including that 1) females seek to confuse paternity and thereby forestall male infanticide and/or ensure male infant care or 2) females seek to ensure fertilization. Assessing the power of fertilization insurance to explain mating patterns in females requires information on the temporal relationship between mating and ovarian hormones. The hormonal correlates of reproduction and mating in free-ranging Propithecus verreauxi were investigated using excreted steroids as indices of reproductive state. Solid-phase extraction and radioimmunoassay techniques were used to measure unconjugated estradiol (E₃) and progesterone (P₄) in 485 desiccated fecal samples collected from five female sifaka before and during the breeding season at Beza Mahafaly, Madagascar. Results suggest that behavioral estrus was characterized by 10- to 15-day elevations in E₂; hormonal activity was observed to be similar to pseudo-estrus reported for other lemur species; apparent conception was associated with sustained P₄ elevations beginning 1 to 3 days post-estrus with gestational phase elevations of E₂ beginning 42 to 45 days post-conception; and mating with multiple partners appeared not to be a prerequisite to fertilization, as conception resulted from both monoandrous and polyandrous matings. These preliminary data suggest that fertilization insurance is not adequate to explain polyandrous mating in sifaka at Beza Mahafaly. © 1996 Wiley-Liss, Inc.     

Information content of sexual swellings and fecal steroids in sooty mangabeys (Cercocebus torquatus atys)

The accuracy and precision of sexual swellings and fecal steroids as measures of ovarian function and the periovulatory period were compared in 4 sexually mature, individually housed, sooty mangabey females. Fecal samples were collected daily over a 10-week period during the normal breeding season. Serum was collected 3×/week, daily during peak swelling, and sex skin was rated 5×/week on a 0–5 relative scale. Both fecal estradiol (fE₂) and progesterone (fP₄) were significantly correlated with serum values in composite E₂-aligned profiles and within the cycles of individual females with average correlations of r_s = 0.6. Follicular phase means for fE₂ and luteal phase means for fP₄ were significantly correlated with the serum means across cycles, suggesting that fecal concentrations could be used to accurately evaluate cycle phases within and across females. In contrast, the timing of peak swelling relative to the periovulatory period varied considerably across the cycles of individual females. Although maximum tumescence appears to bracket the periovulatory period, individual differences in the duration of peak swelling and the timing of its onset and end tend to obscure the exact time of ovulation in relation to maximal tumescence. These data illustrate the utility of fecal steroid analysis as a tool for further evaluation of the signal value of sexual skin and its role in mating interactions. © 1996 Wiley-Liss, Inc.     

Endocrine Correlates of Reproductive Status in Breeding and Nonbreeding Wild Female Moustached Tamarins

In callitrichid primates, reproduction is usually restricted to a single female per group. Reproductive rate is high and the occurrence of a postpartum estrus can lead to simultaneous lactation and pregnancy. In contrast, nonreproductive females often show ovarian inactivity. However, most studies on callitrichid reproductive physiology have been conducted in captivity, where conditions differ considerably from those in the wild, so that reproductive conditions may be strongly modified. Using fecal estrogen and progestogen measurements to monitor female reproductive status in 2 groups of wild moustached tamarins (Saguinus mystax), we examined 1) whether reproductive females in free-ranging groups also show postpartum estrus and 2) whether nonreproductive females demonstrate signs of ovarian activity. In both reproductive females, clear changes in the excretion pattern of progestogen and estrogen metabolites over time in combination with information on parturition dates allowed us to differentiate between pregnancy, a period of postpartum ovarian inactivity lasting for 54 and 64–82 days, and a period of ovarian activity before conception. Nonreproductive females demonstrated temporal fluctuations in hormone concentrations and absolute hormone levels that were similar to ones in the breeding females during the phase of ovarian activity. The results suggest that, in contrast to most captive female tamarins, reproductive females in wild groups of moustached tamarins do not have a postpartum estrus and that nonreproductive females show ovarian activity despite the presence of a breeding female. We therefore conclude that findings from captivity should be only carefully compared to the situation in the wild.     

Birth seasonality and calf mortality in a large population of Asian elephants

In seasonal environments, many species concentrate their reproduction in the time of year most likely to maximize offspring survival. Asian elephants (Elephas maximus) inhabit regions with seasonal climate, but females can still experience 16‐week reproductive cycles throughout the year. Whether female elephants nevertheless concentrate births on periods with maximum offspring survival prospects remains unknown. We investigated the seasonal timing of births, and effects of birth month on short‐ and long‐term mortality of Asian elephants, using a unique demographic data set of 2350 semicaptive, longitudinally monitored logging elephants from Myanmar experiencing seasonal variation in both workload and environmental conditions. Our results show variation in birth rate across the year, with 41% of births occurring between December and March. This corresponds to the cool, dry period and the beginning of the hot season, and to conceptions occurring during the resting, nonlogging period between February and June. Giving birth during the peak December to March period improves offspring survival, as the odds for survival between age 1 and 5 years are 44% higher for individuals born during the high birth rate period than those conceived during working months. Our results suggest that seasonal conditions, most likely maternal workload and/or climate, limit conception rate and calf survival in this population through effects on maternal stress, estrus cycles, or access to mates. This has implications for improving the birth rate and infant survival in captive populations by limiting workload of females of reproductive age. As working populations are currently unsustainable and supplemented through the capture of wild elephants, it is imperative to the conservation of Asian elephants to understand and alleviate the effects of seasonal conditions on vital rates in the working population in order to reduce the pressure for further capture from the wild.     

Reproductive and Life History Parameters of Wild Female <Emphasis Type="Italic">Macaca assamensis</Emphasis>

Information on basic reproductive parameters and life-history traits is crucial for the understanding of primate evolution, ecology, social behavior, and reproductive strategies. Here, we report 4 yr of data on reproductive and life-history traits for wild female Assamese macaques (Macaca assamensis) at Phu Khieo Wildlife Sanctuary, northeastern Thailand. During 2 consecutive reproductive seasons, we investigated reproductive behavior and sexual swelling size in 16 females and collected 1832 fecal samples. Using enzyme immunoassays, we measured fecal estrogen and progesterone metabolites to assess ovarian activity and timing of ovulation and to ascertain conceptions and pregnancies. Timing of reproduction was strictly seasonal (births: April–July, 86% in April–June, 4 yr, n = 29; conceptions: October–February, 65% in December–January, 2 yr, n = 17). Females showed no cyclic ovarian activity outside the mating season and conceived in their first or second cycle (mean: 1.2 cycles to conception, n = 13). Gestation length was on average 164.2 d (range: 158–170, n = 10), and females had their first infant at an age of 5 yr (n = 4). Interbirth intervals were bimodally distributed, with females giving birth on average every 13.9 or 23.2 mo. Shorter interbirth intervals were linked to early parturition within the birth season. Most females displayed subcaudal sexual swellings which, however, did not reliably indicate female reproductive status or fertility. Overall, our results fall within the range of findings reported for other macaque species. These results thus add to the growing body of information available for wild macaques, facilitating comparative studies for a better understanding of interspecific differences in social and reproductive patterns.     

Effects of age,lactation, and repeated cycles on rhesus monkey copulatory intervals

Young, sexually mature female rhesus monkeys copulate on more days prior to conception than do older females, and this prolonged discrete mating period is associated with an earlier rise in serum estradiol prior to the first ovulation of the breeding season. The influence of repeated ovulatory cycles and the presence of a suckling infant on the copulatory patterns were examined in two separate analyses. Extending previous work, young, nulliparous females copulated on more days at the first ovulation of the breeding season than did older, multiparous females. However, the duration of the copulatory period at the second ovulation of the breeding season was similar and significantly shorter for both age groups. Furthermore, the presence of a suckling infant did not influence the duration of the mating periods in adult, multiparous females. The onset of copulatory behavior for all females was associated with serum estradiol concentrations of approximately 90 pg/ml, indicating that the age and cycle differences in the duration of the copulatory periods are due to the time course of serum estradiol prior to ovulation. A separate, longitudinal analysis of the duration of the mating period associated with the first ovulation of three successive breeding seasons indicated that females copulated on more days during their first ovulatory cycle of their first breeding season. These data indicate that the copulatory interval is longer for females during the first ovulation of the breeding season, and this pattern is accentuated in young, sexually mature animals.     

Female reproductive cycles and birth data from an Old World Monkey colony

Observations on reproductive cycles and births for a variety of captive Old World monkey species are reported. The majority of the subjects have been group living animals, housed with conspecifics in large outdoor compounds. Reproductive cycles were measured by notation of changes in the degree of female sex skin swellings. Three types of cycles are distinguished: estrus, intrapregnancy, and pubertal. Cycle length periods and the duration of the period of swelling are described for each cycle type. Birth distributions are analyzed for the occurrence of seasonality, and a marked seasonal effect tied to the onset of cycling in pubescent females is noted. The influence of a group formation effect on the timing of the reproductive season in one species is discussed.