Drinking from arboreal water sources by mantled howling monkeys (Alouatta palliata Gray).

Despite occasional trips to the ground and feeding in trees whose canopies touched the river, mantled howling monkeys were never seen to drink from any ground water. Drinking from arboreal cisterns was observed, but only during the wet season (meteorologically the less stressful season but phenologically the more stressful season). The lack of sufficient new leaves during the wet season forced the howlers to ingest more mature leaves which contained significantly less water. To compensate for the lowered amount of water in their food, the monkeys utilized arboreal water cisterns. The cisterns dried up during the dry season, but the howlers maintained their water balance by altering their time of actiivity and selecting a diet comprised largely of succulent new leaves. The effect of plant-produced secondary compounds on drinking also was discussed.     

Plasma lipoproteins of free-ranging howling monkeys (Alouatta palliata)

1. Plasma lipids and lipoproteins of free-ranging howling monkeys from Costa Rica (Alouatta palliata), aged 5 months to 23 years, were characterized. 2. High density lipoproteins were lipid-rich, similar to HDL2 of human plasma. 3. Fatty acid compositions of major lipid classes of very low, low and high density lipoproteins differed among social groups, possibly due to both dietary and genetic factors. 4. Low and high density lipoprotein phospholipids were enriched in phosphatidylethanolamine. 5. Howler plasma cross reacted with antihuman apoA-I antibodies but not with antihuman LDL antibodies. 6. No dimeric form of apoA-II was present, unlike human apoA-II.     

Breech delivery and birth-related behaviors in wild mantled howling monkeys

The breech birth of an infant mantled howling monkey was observed on February 12, 1990. The mother assisted the successful delivery by pulling on the infant's tail and hindleg. No other members of the social group attended the mother or demonstrated any interest in the birth process.     

A coprological survey of parasites of wild neotropical felidae

In conjunction with an ecological study of jaguars in the Cockscomb Basin of Belize, Central America, fecal samples from jaguars (Panthera onca), jaguarundis (Felis yagouaroundi), ocelots (Felix pardalis), and pumas (Felix concolor) were examined for parasite products (eggs, larvae, and oocysts). Of the 45 samples examined, 39 (86.7%) were positive for parasite products, 23 of 25 (92%) jaguar samples were positive, as were all of the puma (4/4) and ocelot (8/8) samples. Four of 6 samples from unknown species were positive (66.7%). Two jaguarundis samples were negative. The following were identified in the samples: Paragonimus sp. eggs, Taeniidae eggs, Strongylate eggs, Toxocara cati eggs, Toxascaris sp. eggs, Capillaria sp. eggs, Spiruridae eggs, Aelurostrongylus sp. larvae, Oncicola sp. eggs, Hammondia pardalis oocysts, Isospora sp. oocysts, Toxoplasma gondii-like oocysts and Sarcocystis sp. sporocyst.     

Grooming in the mantled howler monkey,Alouatta palliata Gray

Dominant individuals groom subordinates in the mantled howler monkey. This relationship is previously unreported for the species and is a characteristic that howler monkeys share with many birds and mammals.     

Risk factors connected to gastrointestinal parasites in mantled Alouatta palliata mexicana and black howler monkeys Alouatta pigra living in continuous and in fragmented rainforests in Mexico

In this study we document the prevalence of gastrointestinal parasites (helminths and protozoans) found in fecal samples of populations of Alouatta palliata mexicana and of A.pigra in Los Tuxtlas and in Palenque,southeast Mexico,and its relation to habitat condition,sex/age and season.Nineteen parasite morphotypes were detected in the fecal samples from populations of the two howler monkeys,of which 58％ were shared by both species.When considering all parasite species,populations of the two howler species were more likely to be parasitized in fragmented habitat compared to continuous habitat.Individuals of both howler monkey species that lived in fragmented habitat had a higher prevalence of Controrchis biliophilus.A.p.mexicana individuals had a higher prevalence of Trypanoxyuris minutus than A.pigra,probably the result of the larger group sizes found in the former species,and T.minutus was more likely to be found in A.palliata individuals that lived in fragmented habitat.Adult A.p.mexicana males had a higher risk of being parasitized compared to adult females,but these differences were not detected in A.pigra.Parasite species such as Entamoeba sp.,Nematoda sp.28.Nematoda sp.B and Parabronema sp.where only found during the wet season m both howler monkey species.Populations of both howler monkey species had a higher prevalence of Nematoda sp.A in the wet season and Ascaridae eggs were only detected during the wet season in A.pigra.Other parasites detected displayed no clear seasonal pattern.     

Blood groups of the mantled howler monkey (Alouatta palliata).

Fifty-two howler monkeys were tested for their human-type A-B-O blood groups. All were group B, as shown by the presence of B and H in their saliva, and anti-A in serum. The B-like agglutinogen of their red cells is common to all New World monkey species tested, and is of different origin and significance than their true A-B-O blood group. Differences among the B-like agglutinogens of the red cells of howler monkeys, marmosets, rabbits and humans group B were demonstrated, and limited tests have also been performed to study the biochemical basis of the anti-B reactions.     

Behavioral development and socialization of infants in a free-ranging group of howling monkeys (Alouatta palliata)

A 22-month field study was carried out on free-ranging mantled howlers in Costa Rica. Six female and 5 male infants were observed systematically from birth until they died, left the group, or the study ended. Interaction patterns, activity patterns, and proximity data were analyzed from 703 h of focal observations and 753 h of ad lib observations. Developmental trends in weaning and nonmother care were associated with mothers' feeding patterns, suggesting an increase in maternal feeding efficiency. As howler immigration patterns resulted in groups of adults of low relatedness, analyses based on social bonding or kin selection were inappropriate, and socialization patterns instead appeared to prepare howler infants to respond predictably in an adult world. Females, which were more sociable as adults, were also more sociable as infants, initiating interactions and reacting positively. They also exhibited less weaning stress than males. Males, which were forced out of the group sooner, remained solitary longer, and primarily interacted with adult females as adults, were forced to be independent sooner, reacted negatively to interactions, and ceased interacting with adult males by 3 months of age. Ecological constraints on development could not be determined from this study, although there was no evidence for developmental trends being influenced by predator stress.     

Digestive strategies and food choice in mantled howler monkeys Alouatta palliata mexicana: bases of their dietary flexibility

Mantled howler monkeys (Alouatta palliata) occupy a wide variety of tropical habitats and are the most folivorous of New World primates. However, their diet may include fruits, buds, petioles, and flowers, as well as leaves, suggesting they must cope with variations in the nutrient composition of their food. We studied the physiological basis of the dietary flexibility of these monkeys by comparing food choice, digestive performance and patterns of digesta flow in six adults, fed diets of either leaves or a mixture of fruit and leaves. Although monkeys ate similar amounts of the two diets, they ingested more digestible protein when offered the leaf diet, on which they lost body mass, but they ingested much more soluble sugars when offered fruit and leaves on which they gained mass. Digestibilities of dry matter, fat, energy and fibre did not differ between diets, but those of crude protein, soluble sugars and minerals were higher on the fruit–leaf diet. Mean retention times in the gut of solute (Co-EDTA) and particulate markers (Cr-mordanted cell walls) did not differ between diets, but on both diets the monkeys retained the particulate marker (mean retention time ca 55 h) for longer than they did the solute marker (MRT ca 50 h). A lack of selective retention of solutes and small particles in the gastro-intestinal tract of howler monkeys probably restricts them to mixed diets but their digestive strategy is sufficiently flexible to allow them to feed on a diet of leaves when fruit is unavailable.     

Multimodal communication by male mantled howler monkeys (Alouatta palliata) in sexual contexts: a descriptive analysis

We analyzed continuously sampled focal and ad libitum data of male mantled howler monkeys (Alouatta palliata) observed in random order. Males resided in two groups in a Costa Rican tropical dry forest environment (riparian habitat group: 3 males, 15 females, 402 h observation; deciduous habitat group: 2 males, 8 females, 114 h observation). Samples were limited to sexual contexts, in particular, the 60-min periods before and after each copulation observed within each group for each male. Time samples for each male were distributed equally before and after their own copulations. Before statistical analyses were conducted, data were corrected for differences in time sampled for males within each group. Four types of multimodal signaling were resolved: (1) audiovisual, (2) olfactory-visual, (3) olfactory-visual-tactile and (4) tactile-gustatory. Olfactory and tactile signals were never observed in combination with auditory signals. Consistent with expectation for a Neotropical, arboreal species, audiovisual signals were the most frequently observed type of multimodal communication in both groups (riparian habitat group: n = 139; deciduous habitat group: n = 66). Our evidence strongly suggests that unimodal signals may be combined and recombined to form complex, multimodal signals. Subordinate males in each group were more likely than dominant males to emit audiovisual signals before their own copulations. Male dyads were compared to assess the relative rate of audiovisual signaling by one male before another male's copulations. On average, the subordinate male of the riparian habitat group exhibited audiovisual signals at a higher rate before his own copulations compared to the rate of audiovisual signaling by his dominant challengers. The same comparisons are not significant for males in the deciduous habitat group. The pattern of male response that we report whereby subordinates emit some complex signals at a higher rate than dominants supports the 'terminal investment hypothesis' predicting that organisms should increase reproductive effort with age since, in mantled howlers, age correlates negatively with dominance rank. Additional, qualitative observations suggested that subordinates in both groups were most likely to obtain copulations when they increased rates of complex signaling and/or escalated interactions with their male challengers. Group differences were apparent, however, and we suggest factors that may account for these patterns. We assessed responses by female receivers of complex signals emitted by males in sexual contexts. In general, higher-ranking males are more attractive to females and are more successful at monopolizing them. Findings for other, less frequently displayed, multimodal signals (olfactory-visual, olfactory-visual-tactile and tactile-gustatory) are presented and discussed. We conclude with the suggestion that howlers may be a robust model for the investigation of complex signals in Neotropical primates, including research on functionally referential communication and context-dependent syntax.     

Fruit eating and seed dispersal by howling monkeys (Alouatta palliata) in the tropical rain forest of Los Tuxtlas,Mexico

The frugivory and ranging habits of howling monkeys living in the rain forest of Los Tuxtlas, Veracruz, Mexico, were studied for 5 consecutive years with the aim of investigating the role of seed dispersal agents played by the howling monkeys. The howling monkeys' consumption of fruit occupied half of their feeding time, and 80% of this time was spent feeding on mature fruit. Observations confirmed use of 19 tree species and a preference for a few species of Moraceae and Lauraceae. Fruit exploitation was very seasonal; only two species provided fruit year-round. Home range size was about 60 ha, and animals in the troop (N = 16) showed a day range of 10–893 m. Monthly collection of fecal samples during 2 years indicated that 90% of the seeds (N = 7,928) in the samples belonged to eight tree species and to one liana; the rest belonged to 15 unidentified species of vines. Germination success for the seeds in the feces was about 60% and for control seeds was 35%. Howling monkeys created diverse seed shadows in the vicinity of their leaf and fruit sources, and while they dispersed the seeds of some plant species, they also produced a great deal of fruit and seed waste for others.     

Intestinal parasites in howler monkeys Alouatta palliata (Primates: Cebidae) of Costa Rica

Fecal samples of 102 howler monkeys (Alouatta palliata) from several sites of Costa Rica were studied for intestinal parasites. The zones studied were: Central Valley (San Ramón, Alajuela), Central Pacific (Chomes and Manuel Antonio National Park. Puntarenas), North Pacific (Palo Verde Park and Playa Potrero, Guanacaste). Chira Island in the Nicoya Gulf and Caribean area (Cahuita. Limón). Animals were anesthetized with dards containing Telazol in order to collect the fecal material; some monkeys defecated spontaneously and others by direct stimulation. Samples were studied in saline solution (0.85%) and a Iodine solution, or stained with Haematoxylin. The material was also cultured in Dobell culture medium to determine the presence of amoeba and flagellates. Strongvloides. Controrchis. Trypanoxyuris genera were found in 3.4% of the samples. In addition 16.7% to 80% of the animals showed protozoa infection with Endolimax, Entamoeba, Trichomonas and Giardia. It is discussed the relationships of parasite infection with environmental conditions, animal population and human presence, specially in the monkey conservation programs point of view.     

Reproduction and population growth in free-ranging mantled howling monkeys

Free-ranging mantled howling monkey (Alouatta palliata Gray) females experienced a regular estrus cycle averaging 16.3 days, demonstrated sexual skin changes, and participated in multiple matings before becoming pregnant. Gestation averaged 186 days. The average interval between births was 22.5 months. Sexual maturity occurred at approximately 36 and 42 months for females and males, respectively. Female age at first birth was about 3½ years. Births were scattered during some years and clustered during others. The age, rank, and parity of the females affected infant survival. More female than male infants survived to one year of age. Increased population size was the result of immigration rather than births.     

Habitat selection and seasonal patterns of activity and foraging of mantled howling monkeys(Alouatta Palliata) in Northeastern Costa Rica

I conducted a 15- month ecological study of habitat preferences and activity and foraging patterns of two troops of mantled howling monkeys, Alouatta palliata,in a lowland rain forest at La Selva Biological Reserve in northeastern Costa Rica. The two troops specialized on different habitats in spite of the fact that both of them had all habitats available and were not constrained by neighboring troops since the population density of howlers is low (7- 15 howlers/km ² ).Troop 1 spent the majority of time in primary forest (80%) followed by secondary forest (10%), while troop 2 spent the majority of time in undisturbed riparian habitat (60%) followed by primary forest (30%). Habitat sampling indicates that neither the total number of stems, species, or families nor the diversity (Shannon index) or evenness is a good indicator for howler habitat selection. Instead the density of trees from the 12 species most commonly consumed by each troop is the most important factor. Activity and foraging patterns were not dependent upon the season as has been described for howling monkeys in forests with a more pronounced dry season at Barro Colorado Island, Panama, and La Pacifica in northwestern Costa Rica. This is likely a result of the more constant food supply at La Selva, combined with less intraspecific competition due to the low howler density. The intraspecific variability of foraging patterns and troop- specific habitat specialization observed in Alouatta palliatashould be considered in the conservation biology of primates. Primate relocation programs should include not only an ecological assessment of the release site but also a comparison of the release site with the habitat that the groups currently occupy.     

Natural selection on molar size in a wild population of howler monkeys (Alouatta palliata)

Dental traits have long been assumed to be under selection in mammals, based on the macroevolutionary correlation between dental morphology and feeding behaviour. However, natural selection acting on dental morphology has rarely, if ever, been documented in wild populations. We investigated the possibility of microevolutionary selection on dental traits by measuring molar breadth in a sample of Alouatta palliata (mantled howler monkey) crania from Barro Colorado Island (BCI), Panama. The age at death of the monkeys is an indicator of their fitness, since they were all found dead of natural causes. Howlers with small molars have significantly decreased fitness as they die, on average, at an earlier age (well before sexual maturity) than those with larger molars. This documents the existence of phenotypic viability selection on molar tooth size in the BCI howlers, regardless of causality or heritability. The selection is further shown to occur during the weaning phase of A. palliata life history, establishing a link between this period of increased mortality and selection on a specific morphological feature. These results provide initial empirical support for the long-held assumption that primate molar size is under natural selection.     

Non-visual senses in fruit selection by the mantled howler monkey (Alouatta palliata)

Primates - There is extensive knowledge about the visual system and the implications of the evolution of trichromatic color vision in howler monkeys (genus Alouatta) related to food selection;...     

Exploration and play in howler monkeys (Alouatta palliata)

Exploration and play were observed in eight troops of howler monkeys (Alouatta palliata) containing 56 young and 95 adults. The behavior patterns of seven age classes are described. There was a clear trend for animals to spend less time in nonsocial exploration with increasing age, and for the frequency of social play to follow an inverted “U” pattern, peaking in the early juvenile stage at 15–30 min per day. The howlers' specialization for eating large quantities of difficult to digest plant matter affected their play: as the young became increasingly dependent on plant food around the infants stage, there was a shift in their playtimes to allow for the energy demanding activity of digestion. This and other aspects of howler behavior are related to a reinforcement theory of exploration and play.