Vertical clinging, small body size, and the evolution of feeding adaptations in the Callitrichinae.

Primates of the subfamily Callitrichinae (Callimico, Callithrix, Leontopithecus, and Saguinus) are small-bodied New World monkeys (105-700 g) possessing clawlike nails on all manual and pedal digits excluding the hallux. Specialized nails in these genera serve a critical function in feeding by enabling tamarins and marmosets to cling to trunks and other large vertical supports while exploiting food resources. Within the subfamily, there is evidence of at least four distinct large-branch feeding patterns. These include (1) seasonal exudate feeding and occasional trunk foraging (many Saguinus spp.); (2) exploitation of bark surface insects and the use of trunks as a platform to locate terrestrial prey (Saguinus fuscicollis, S. nigricollis, and Callimico); (3) manipulative foraging and bark stripping to locate concealed insects and small vertebrates (Leontopithecus); and (4) tree gouging and year-round exudate feeding (many Callithrix). Large-branch feeding and the use of vertical clinging postures appear to be a primary adaptation among virtually all callitrichines, distinguishing them ecologically from other platyrrhine taxa. Given the anatomy and behavior of extant callitrichines, Saguinus appears to be the most ecologically generalized member of this subfamily, and species of this genus may provide useful models for reconstructing the feeding and foraging adaptations of early callitrichines.     

Gum feeder as environmental enrichment for zoo marmosets and tamarins

Tamarins and marmosets are small-bodied social callitrichines. Wild callitrichines feed on exudates, such as sap and gum; particularly, marmosets are mainly gummivores, while tamarins consume gums only occasionally and opportunistically. Zoo marmosets and tamarins are usually provided with gum arabic as an alternative to the exudates normally found in the wild. The aim of this study was to evaluate the effects of a gum feeder on the behavior and well-being of four zoo-managed callitrichines. We studied four cotton-top tamarins (Saguinus oedipus), four red-handed tamarins (S. midas), two pygmy marmosets (Cebuella pygmaea), and three Geoffroy's marmosets (Callithrix geoffroyi) housed at Parco Natura Viva (Italy). We conducted the study over two different periods, a baseline (control, without the gum feeder) and then a gum feeder (when the gum feeder was provided) period. We used continuous focal animal sampling to collect behavioral data, including durations of social and individual behaviors. We collected 240 min of observations per period per study subject, with a total of 3,120 min for all the subjects in the same period and of 6,240 min in both periods. We analyzed data by using nonparametric statistical tests. First, we found that the gum feeder promoted species-specific behaviors, such as exploration, and diminished self-directed behaviors, suggesting an enriching effect on tamarin and marmoset behavior. Moreover, in red-handed tamarins, the provision of the gum feeder reduced the performance of self-directed and abnormal behavior, specifically coprophagy. These results confirm that gum feeders are effective foraging enrichment tools for zoo marmosets and tamarins.     

Hand specialization, sympatry, and mixed-species associations in callitrichines

Hand morphology in callitrichines (i.e., tamarins, marmosets, and Goeldi's monkey) is correlated with positional and foraging behaviors. This study examines hand shape in callitrichines using an allometric approach. It addresses a series of questions relating hand anatomy, insect foraging behavior, and resource partitioning in callitrichines. The main questions are: 1. Do the hands of Leontopithecus differ in shape from all other callitrichine taxa allowing it to perform highly manipulative prey foraging behaviors? 2. Are the hands of Saguinus fuscicollis adapted to manipulative foraging, and are they functionally similar to Leontopithecus' hands? 3. Is hand morphology in S. fuscicollis more similar to the hand morphology of sympatric tamarin species with whom it does not form mixed species troops (S. nigricollis and S. tripartitus) than to those sympatric tamarin species with whom it does form mixed troops (S. mystax, S. labiatus, and S. imperator)? Measurements of hand length (HL), width (HW), and thickness (HT) were taken from 1350 museum specimens of callitrichines (Callithrix, Cebuella, Leontopithecus, Saguinus, and Callimico), squirrel monkeys (Saimiri), and owl monkeys (Aotus). The analysis indicates that hand shape covaries with foraging strategy. Specifically, the hands of Leontopithecus are adapted for manipulative foraging and are relatively longer and more slender than the hands of other callitrichines. A similar pattern is observed in the hands of S. fuscicollis, S. tripartitus and S. nigricollis. These latter species, however, differ significantly in shape from all other tamarin species. Large differences in hand morphology are observed among tamarin species that form mixed-species troops. These anatomical differences may permit resource partitioning and coexistence among these closely related taxa. Hand shape, expressed as log HLGM (logged hand length divided by the geometric mean of all measurements), is a good predictor of manipulative and non-manipulative prey foraging techniques employed by callitrichines.     

Reproduction in captive lion tamarins (Leontopithecus): Seasonality,infant survival,and sex ratios

Diversity in reproductive and social systems characterizes the primate family Callitrichidae. This paper contributes to our appreciation of this diversity by presenting the first detailed comparative analysis of captive breeding in three species of lion tamarins (Leontopithecus chrysomelas, L. chrysopygus, and L. rosalia) housed at the Centro de Primatologia do Rio de Janeiro. The annual pattern of reproduction in all three species of Leontopithecus was markedly seasonal, with births occurring during the spring, summer, and fall months from August through March. While modal number of litters produced per female per year was 1, approximately 20% of breeding females produced two litters per year. The onset of breeding activity in years when two litters are produced was significantly earlier than in years when only one litter was produced. The cumulative number of offspring surviving to 3 months of age did not differ between years with one vs. two breeding attempts. Like other callitrichids, postnatal mortality was highest during the first week of life, and there were pronounced species differences in offspring survival through 1 year, with significantly lower survivorship in L. chrysomelas. Infant survivorship was affected by a number of experiential factors. Survivorship up to 30 days of life was higher in groups in which the breeding female had previous experience with infants as a nonbreeding helper than in groups in which the female lacked previous helping experience. Likewise, survivorship to 30 days of life was higher for infants born to multiparous females than for infants born to primiparous females. When parity and previous helping experience were analyzed concurrently, the lowest survivorship was associated with offspring produced by inexperienced primiparous females. Genus-wide, there was no significant departure from a 50:50 sex ratio at any point during the first year of life, nor was there evidence for differential mortality for male and female infants. However, L. chrysopygus produced significantly more male infants at birth (65:44) and had male-biased litters (approximately 60% males) throughout the first year of life, while L. chrysomelas showed a nonsignificant tendency toward female-biased litters. © 1996 Wiley-Liss, Inc.     

Reproduction of the emperor tamarin (Saguinus imperator) in captivity,with comparisons to cotton-top and golden lion tamarins

Little information has been published on the reproductive biology and behavior of the emperor tamarin (Saguinus imperator). We analyzed twelve years of data on emperor tamarins at the Los Angeles Zoo and made comparisons with data on cotton-top tamarins (Saguinus o. oedipus) and golden lion tamarins (Leontopithecus rosalia) from the same collection. Secondary sex ratios did not differ significantly from 50:50. Births were not strictly seasonal for any species. The number of infants reared had a significant effect on interbirth interval for all species, with shorter intervals when only one or no infants were reared, but females did sometimes conceive early in lactation. In emperor tamarin families, all fathers and most older siblings carried new infants, usually beginning within a few days after a birth. Previous exposure to younger siblings did not appear to be critical to the development of competent parental behavior by zooborn emperor tamarin females.     

Update on the Phylogenetic Systematics of New World Monkeys: Further DNA Evidence for Placing the Pygmy Marmoset (Cebuella) within the Genus Callithrix

We determined DNA sequences spanning the 1.8-kb long intron 1 of the interstitial retinol-binding protein nuclear gene (IRBP) for Callithrix geoffroyi, Callithrix humeralifer, and Callithrix argentata. With the 22 previously determined IRBP intron 1 sequences—21 from the 16 currently recognized genera of New World monkeys—the enlarged IRBP data represent for the marmoset genus Callithrix both its argentata and its jacchus species groups. Maximum-parsimony and neighbor-joining trees, constructed for the 25 aligned IRBP intron 1 sequences, support a provisional phylogenetic classification with three families: Atelidae, containing subfamily Atelinae; Pitheciidae, containing subfamily Pitheciinae; and Cebidae, containing subfamilies Cebinae, Aotinae, and Callitrichinae. In order to have taxa at the same hierarchical rank at equivalent age, this classification has all living callitrichines in a single tribe, Callitrichini, with four subtribes: Saguinina (Saguinus), Callimiconina (Callimico), Leontopithecina (Leontopithecus), and Callitrichina (Callithrix with the pygmy marmoset, Cebuella pygmaea, merged into it). The DNA evidence shows not only that Callithrix must include C. pygmaea to be monophyletic but also that the times of separation of pygmaea and the argentata and jacchus species groups from one another are to be expected (<5 Ma—million years ago) for species in a single genus. On relating the time course of the ceboid radiation to biogeographic information, it appears that in mid-Miocene times (10–11 Ma) a basal callitrichin stock branched into the ancestral population of Saguinus in one clade and the ancestral population of Leontopithecus and Callimico–Callithrix (or Leontopithecus–Callimico and Callithrix) in another clade. The proto-lion tamarins migrated south and eastward, where they were isolated in refugia, becoming the genus Leontopithecus. The stock remaining in Amazonia gave rise to present-day Callimico and Callithrix. The latter genus occupied a vast geographic area, giving rise to the argentata and pygmaea groups in Amazonia and to the jacchus group in central and eastern Brazil.     

Environmental Enrichment for New World Primates: Introducing Food-Irrelevant Objects and Direct and Secondary Effects

This study examined methods of environmental enrichment for zoo animals for 4 New World primate species: pygmy and Geoffrey's marmosets (Cebuella pygmaea and Callithrix geoffroyi), red-bellied tamarins (Saguinus labiatus), and golden- headed lion tamarins (Leontopithecus chrysomelus). Subjects were housed in groups at the Philadelphia Zoo. Baseline behavioral time budget data were collected, and stimulus objects were then introduced in succession to each enclosure. Each object included multiple manipulable subcomponents. Time budget data were collected while objects were in the enclosures, and subjects' contacts with objects were videotaped. Overall time budgets were significantly altered in only the red-bellied tamarins, the least active of the species, solely due to a shift from social grooming to passive social contact; when categories were collapsed into broader categories, this effect disappeared. Object contact occurred within the 1st hr for all species and ranged over nearly 2 orders of magnitude, from approximately 10 sec per subject (red-bellied tamarins) to approximately 700 sec per subject (Geoffrey's marmosets). Habituation was not evident within any 1st hr of observation but was shown when 1st hr observations were compared with those from subsequent days. This article discusses implications for environmental enrichment in zoos.     

Environmental Enrichment for New World Primates: Introducing Food-Irrelevant Objects and Direct and Secondary Effects

This study examined methods of environmental enrichment for zoo animals for 4 New World primate species: pygmy and Geoffrey's marmosets (Cebuella pygmaea and Callithrix geoffroyi), red-bellied tamarins (Saguinus labiatus), and golden- headed lion tamarins (Leontopithecus chrysomelus). Subjects were housed in groups at the Philadelphia Zoo. Baseline behavioral time budget data were collected, and stimulus objects were then introduced in succession to each enclosure. Each object included multiple manipulable subcomponents. Time budget data were collected while objects were in the enclosures, and subjects' contacts with objects were videotaped. Overall time budgets were significantly altered in only the red-bellied tamarins, the least active of the species, solely due to a shift from social grooming to passive social contact; when categories were collapsed into broader categories, this effect disappeared. Object contact occurred within the 1st hr for all species and ranged over nearly 2 orders of magnitude, from approximately 10 sec per subject (red-bellied tamarins) to approximately 700 sec per subject (Geoffrey's marmosets). Habituation was not evident within any 1st hr of observation but was shown when 1st hr observations were compared with those from subsequent days. This article discusses implications for environmental enrichment in zoos.     

Litter size and infant survivorship in wild groups of cotton‐top tamarins (Saguinus oedipus) in Colombia

Cotton‐top tamains (Saguinus oedipus) are a critically endangered primate found only in Colombia. Efforts to conserve this species are centered on developing effective management plans that integrate biological information regarding population dynamics and factors that influence their survival. This study documented infants born to wild cotton‐top tamarin females from 1994–2008 at two distinct field sites in northern Colombia. Our studies have shown that wild cotton‐top tamarins typically give birth to one litter each year and infant survival to 6 months of age was greater in the wild than has been reported in captive colonies. However, similar to reports from captive colonies, litter size of wild cotton‐top tamarins ranges from 1–3 infants, with twin litters most common. Here we report the first occurrence of triplet litters in nearly 20 years of observing wild cotton‐top tamarin groups. Over the first 3 months of life, wild‐born infants exhibited highest mortality during the first week of life, similar to reports from captive colonies. Infant survival in the wild also increases with successive litters as it does in captivity. However, inter‐birth interval, group size, and the number of adult males in the group did not appear to influence infant survival in the wild. The value of such long‐term data from field studies aids in the information that can be used to model future population trends and develop effective conservation plans for this critically endangered primate. Am. J. Primatol. 71:707–711, 2009. © 2009 Wiley‐Liss, Inc.     

Differences among captive callitrichids in the digestive responses to dietary gum

Although many members of the Callitrichidae, a monophyletic family of small, New World monkeys, have been observed to feed on plant exudates, available field data support the generalization that pygmy and common marmosets (Cebuella pygmaea and Callithrix jacchus) feed on gums to a greater extent than most other callitrichids. Because microbial fermentation is required for vertebrates to digest gums, gum-feeding primates may react differently to dietary gum from their relatives that eat little gum. To test this hypothesis, digestion trials were conducted on animals from the two marmoset species, two tamarin species (Saguinus fuscicollis and S. oedipus), and a species of lion tamarin (Leontopithecus rosalia). These species span the range of body sizes within the Callitrichidae. All animals were fed two variations of a homogeneous diet, which differed only in that gum arabic was added to one. Transit time of digesta (TFA) and digestive efficiency (as measured by the coefficients of apparent digestibility of dry matter and energy [ADDM and ADE, respectively]) were compared between diets for each individual. As predicted, the digestive responses of marmosets differed from the responses of the other study species. In marmosets, TFA tended to be longer when gum was added to the diet, while TFA did not change in the other three species. Digestive efficiency decreased in tamarins and lion tamarins with the addition of gum to the diet; marmoset digestive efficiency was unaffected by diet. The results of this research are consistent with the hypothesis that marmosets have digestive adaptations that aid in the digestion of gum that other callitrichids lack. © 1996 Wiley-Liss, Inc.     

Taste thresholds and above-threshold responses to fructose solution in relation to diet in Callitrichidae primates]

Taste thresholds and consumption responses to above-threshold concentrations of fructose solutions were determined in eight callitrichid primate species using the "two-bottle preference test". Although taste thresholds are relatively similar across species, above-threshold responses may differ considerably between marmosets and tamarins. As fructose concentration increases, the rate of consumption increases less for most marmoset species (Cebuella and Callithrix spp.) than for Goeldi's monkey (Callimico) and tamarins (Saguinus and Leontopithecus spp.). It is proposed that distinct shapes of the curves illustrating these responses characterize species in terms of global taste system adaptations to different diets.     

Cross-generic Food Sharing in Tamarins

Adult-infant food-sharing behavior is a major component of the infant care strategies of callitrichids (marmosets and tamarins). It is particularly well-developed in cotton-top tamarins (Saguinus Oedipus) and lion tamarins (Leontopithecus spp), which show frequent adult-initiated food offering, as well as sharing of food in response to begging by infants. This report documents a case of cross-generic food sharing, in which a male golden-headed lion tamarin (Leontopithecus chrysomelas) shared food with an infant cotton-top tamarin. The lion tamarin provided more food to the infant than its mother did. This emphasizes the importance of this behavior in the reproductive strategies of the communally-rearing Callitrichidae and raises questions about mechanisms that underly it.     

The place of Callimico goeldii in the Callitrichine phylogenetic tree: evidence from von Willebrand factor gene intron II sequences

Sequences of a 0.9-kb DNA segment spanning intron 11 of the von Willebrand Factor gene (vWF) were determined for 21 individuals of 19 primate species. The results of maximum parsimony and maximum likelihood analyses of these vWF sequences are congruent with previous molecular findings from other nonlinked nuclear genomic loci which divide the platyrrhine superfamily Ceboidea into three monophyletic families: Cebidae, Atelidae, and Pitheciidae. The vWF results strongly support the taxon Callitrichinae as a monophyletic subfamily within Cebidae. The four extant callitrichine genera constitute tribe Callitrichini, and the basal branchings within this tribe first separate out Saguinus (tamarins), next Leontopithecus (lion tamarins), and last the sister genera Callimico (Goeldi's monkeys) and Callithrix (marmosets). Callithrix divides into three subclades, with pygmy marmosets (C. pygmaea) as sister of the C. argentata species group and with the C. jacchus species group as their sister. Fossil and DNA evidence place the emergence of the callitrichine clade in the basal cebid radiation at about 20 Ma (million years ago) and the three basal branchings in the callitrichin radiation at about 13 to 11 Ma. In turn, the branchings separating the three subclades of Callithrix are placed at about 5 to 4 Ma.     

Cotton-top tamarins (Saguinus (o.) oedipus) in a semi-naturalistic captive colony

To test the prediction that the breeding success of captive cotton-top tamarins (Saguinus (o.) oedipus) could be improved by maintaining them in groups whose size and age-sex composition resembled those of wild groups, data were collated from 6.5 years of records from a breeding colony that otherwise had housing and husbandry procedures similar to those of other successful colonies. Group size and composition in the colony closely resembled those of wild groups, and infant survival was the highest yet reported for the species, with 69% of the 124 infants born reared by their parents to adulthood, and a mean surviving litter size of 1.5 infants. Abortion, stillbirth, and parental neglect of infants were rare. Parity had several effects on reproduction: mean litter size decreased, but percentage infant survival increased; interbirth intervals decreased in length; and seasonality in reproduction was more pronounced for the first four litters born to breeding females than for their subsequent litters, with a birth peak in the spring. Although a spacious and complex physical environment, retention of offspring in their natal families until experience of several sets of infant siblings had been obtained, and non-invasive husbandry and research techniques may all have contributed to the colony's success, it seems possible that the improvement over other colonies is due to the resemblance of group composition to those of wild tamarins.     

Platyrrhine juvenile mortality in captivity and in the wild

I reviewed literature on juvenile mortality in the Platyrrhini in order to evaluate reproductive success in captive breeding. Juvenile mortality includes abortion, premature mortality, stillbirth and death of the unweaned young. The highest losses occur in the Callitrichidae (31% through 3 months of age; 86% through 6 months of age) and in Lagothrixspp. (around 50% through 1 month of age) among the Cebidae. High abortion rates occur in Saguinusand Aotus.High stillbirth incidences are reported for the Callitrichidae (Callithrixand Saguinus)and for the Cebidae (Saimiriand Aotus).Although most mortality occurs in the first week for most species, a considerable proportion of deaths occurs in the period from week 1 until weaning. Important causes of death are trauma and aberrant parental behavior. Prematurity plays an important role in perinatal death among the Callitrichidae. Dystocia is a major cause of stillbirth in Saimiri. Congenital malformations occur in Callithrix, Saguinus, Leontopithecus,and Saimiri.Infectious diseases play a secondary role in mortality, particularly during the first period of life. A higher mortality risk is present if the infant is male, if the litter size is different from two (Callitrichidae), if the mother is primiparous, captive born, or inexperienced, or if the group is small (Callitrichidae) or unstable (Cebidae).     

The functional correlates of jaw‐muscle fiber architecture in tree‐gouging and nongouging callitrichid monkeys

Common (Callithrix jacchus) and pygmy (Cebuella pygmaea) marmosets and cotton‐top tamarins (Saguinus oedipus) share broadly similar diets of fruits, insects, and tree exudates. Marmosets, however, differ from tamarins in actively gouging trees with their anterior dentition to elicit tree exudates flow. Tree gouging in common marmosets involves the generation of relatively wide jaw gapes, but not necessarily relatively large bite forces. We compared fiber architecture of the masseter and temporalis muscles in C. jacchus (N = 18), C. pygmaea (N = 5), and S. oedipus (N = 13). We tested the hypothesis that tree‐gouging marmosets would exhibit relatively longer fibers and other architectural variables that facilitate muscle stretch. As an architectural trade‐off between maximizing muscle excursion/contraction velocity and muscle force, we also tested the hypothesis that marmosets would exhibit relatively less pinnate fibers, smaller physiologic cross‐sectional areas (PCSA), and lower priority indices (I) for force. As predicted, marmosets display relatively longer‐fibered muscles, a higher ratio of fiber length to muscle mass, and a relatively greater potential excursion of the distal tendon attachments, all of which favor muscle stretch. Marmosets further display relatively smaller PCSAs and other features that reflect a reduced capacity for force generation. The longer fibers and attendant higher contraction velocities likely facilitate the production of relatively wide jaw gapes and the capacity to generate more power from their jaw muscles during gouging. The observed functional trade‐off between muscle excursion/contraction velocity and muscle force suggests that primate jaw‐muscle architecture reflects evolutionary changes related to jaw movements as one of a number of functional demands imposed on the masticatory apparatus. Am J Phys Anthropol, 2009. © 2009 Wiley‐Liss, Inc.     

Model life tables for the smaller new world monkeys

Mortality statistics from five populations of small New World monkeys (includinsg Callithrix jaccus, Leontopithecus rosalia, Saguinus fuscicollis, and Saguinus oedipus) were combined to generate a standard model life table reflecting the mortality patterns of these primates. The model is applied to three individual populations to illustrate a strategy for smoothing and interpolating mortality statistics of varying completeness and quality. © 1993 Wiley-Liss, Inc.     

Phylogenetic relationships of the New World monkeys (Primates, platyrrhini) based on nuclear G6PD DNA sequences

In order to test hypotheses about the phylogenetic relationships among living genera of New World monkeys, 1.3 kb of DNA sequence information was collected for two introns of the glucose-6-phosphate dehydrogenase (G6PD) locus, encoded on the X chromosome, for 24 species of New World monkeys. These data were analyzed using a maximum parsimony algorithm. The strict consensus of the three most-parsimonious gene trees that result shows support for the following clades: a pitheciine clade including Callicebus within which Chiropotes and Cacajao are sister taxa, an Alouatta-atelin clade within which Brachyteles is the sister taxon of Lagothrix and which is sister to another clade containing the callitrichines, and a callitrichine/Aotus/Cebus/Saimiri clade. Within the callitrichines, Callimico is the sister taxon of Callithrix. Cebus and Saimiri form a clade. These results are broadly consistent with previously published DNA sequence analyses of platyrrhine phylogeny and provide additional support for groupings provisionally proposed in those earlier studies. Nevertheless, questions remain as to the relative phylogenetic placement of Leontopithecus and Saguinus, the branching order within the Aotus/Cebus/Saimiri/callitrichine clade, and the placement of the pitheciine clade relative to the atelines and the callitrichines.     

Do mothers prefer helpers or smaller litters? Birth sex ratio and litter size adjustment in cotton-top tamarins (Saguinus oedipus)

Sex allocation theory has been a remarkably productive field in behavioral ecology with empirical evidence regularly supporting quantitative theoretical predictions. Across mammals in general and primates in particular, however, support for the various hypotheses has been more equivocal. Population‐level sex ratio biases have often been interpreted as supportive, but evidence for small‐scale facultative adjustment has rarely been found. The helper repayment (HR) also named the local resource enhancement (LRE) hypothesis predicts that, in cooperatively breeding species, mothers invest more in the sex which assists with rearing future offspring and that this bias will be more pronounced in mothers who require extra assistance (i.e., due to inexperience or a lack of available alloparents). We tested these hypotheses in captive cotton‐top tamarins (Saguinus oedipus) utilizing the international studbook and birth records obtained through a questionnaire from ISIS‐registered institutions. Infant sex, litter size, mother's age, parity, and group composition (presence of nonreproductive subordinate males and females) were determined from these records. The HR hypothesis was supported over the entire population, which was significantly biased toward males (the “helpful” sex). We found little support for helper repayment at the individual level, as primiparous females and those in groups without alloparents did not exhibit more extreme tendencies to produce male infants. Primiparous females were, however, more likely to produce singleton litters. Singleton births were more likely to be male, which suggests that there may be an interaction between litter size adjustment and sex allocation. This may be interpreted as supportive of the HR hypothesis, but alternative explanations at both the proximate and ultimate levels are possible. These possibilities warrant further consideration when attempting to understand the ambiguous results of primate sex ratio studies so far.     

Correlates of molt in golden lion tamarins (Leontopithecus rosalia)

In this paper we describe the timing and correlates of molt for a native population of golden lion tamarins (Leontopithecus rosalia). We conducted 820 examinations of 267 adult tamarins over a 7.75 year period to determine the annual molting cycle in this population. Dorsal molt was an annual event for most individuals in the study population; however, 10% of sampled individuals apparently molted twice in a 12 month period. Duration of molt was estimated at 5–6 weeks. The proportion of samples in which tamarins were in molt was significantly greater during the wet season than the dry season and positively correlated with mean monthly precipitation and minimum temperature but not tamarin births, suggesting an environmental component to timing of molt. We found no sex differences in the occurrence of molt during wet or dry seasons. However, the relative frequency of samples in molt was significantly less for gravid females than for nongravid females. In four polygynous groups, socially dominant females gave birth before subordinate females, and younger reproductive females completed molt before older reproductive females. © 1995 Wiley-Liss, Inc.