Effects of black howler monkey (Alouatta caraya) seed ingestion on insect larvae

Fig (Ficus monckii) and laurel (Ocotea puberula) seeds were obtained from Alouatta caraya feces (ingested seeds) and from trees (noningested) in northeastern Argentina. Seeds were examined to detect the presence (infested) or absence (noninfested) of larvae. Sixty percent (N = 315) of noningested fig seeds were galls with insect larvae inside, while 23% (N = 331) were encountered in the ingested group. Eighty-two percent (N = 28) of noningested laurel seeds were infested, and only 19% (N = 63) of ingested seeds were infested. According to the present data, the insects' larvae are digested by howlers intaking animal protein, but the laurel seeds were not destroyed. Am. J. Primatol. 45:411–415, 1998. © 1998 Wiley-Liss, Inc.     

Birth Seasonality in Alouatta caraya in Northern Argentina

Given appropriate ecological and social conditions, natural selection should favor individuals that can concentrate their reproductive events to a particular time of the year that offers high opportunities for infant survivorship. Previous studies on births in Alouatta caraya in Northern Argentina revealed the existence of a peak during the dry season—a period with scarcity of food resources—in mainland gallery forest (G. E. Zunino, Extra 133: 1–10, 1996). The time of conception and the period of independence of the offspring are positively correlated with precipitation, temperature and availability of food. Offspring became independent from their mothers when the availability of resources was high, and conception coincided with the peak of fruit production. Our goal was to examine patterns of birth seasonality in Alouatta caraya in flooded forest on an island in Northern Argentina for comparison with the mainland population. Both sites are at similar latitudes, but differ in forest type. The results indicate that the availability of new and mature leaves is more consistent throughout the year in the flooded forest (p<0.05); however, there was no difference in the availability of fleshy fruits between sites (p>0.05). The pattern of births differed between the gallery forest and the flooded forest (2-way Anova, p<0.001). In the flooded forest births occurred throughout the year, which supports the contentions that howlers do not have a fixed birth season and that the observed variation in the timing of births appears to represent a facultative behavioral response to changes in food availability.     

A study of a black howling monkey (Alouatta caraya) population in northern Argentina

A population of Alouatta caraya in northern Argentina had an ecological density of 130 animals per km². Mean troop size varied from 7.2 to 8.9 individuals, and the ratio of adult males to adult females from 0.58 to 0.51. Infants comprised from 6% to 14% of the population, juveniles from 16% to 21%. These percentages probably vary seasonally in response to a birth peak at the beginning of the dry season. Males were age-graded in multi-male troops. Sexual dimorphism was extreme in this species. Males were all black and averaged 6.7 kg; females were yellow-brown and averaged 4.4 kg. Juvenile males retained the pelage color of the female until approximately 4.5 yr of age and 5 kg in weight. No genital mimicry or exaggeration occurred in this species. Vocalizations of A. caraya were similar to those of A. seniculus, both of which tend to be lower pitched than those of A. palliata.     

Red howler monkey birth data I: Seasonal variation

A large set of birth data from a population of red howler monkeys (Alouatta seniculus) in two habitats found a consistent birth “dip,” with births occurring less frequently in early wet season (May–July) than during the remaining months. In one of two habitats, births were negatively correlated with rainfall, and viable conceptions were positively correlated with rainfall. The observed degree of within-troop birth synchrony appeared to reflect populational synchrony with environmental factors. Correlations between births and the phenology of plant foods were not striking, but there was weak support for the hypothesis that births are timed to maximize the availability of weaning foods. Reduced births in early wet season also minimize the number of Infants who would experience the transition to independent locomotion and feeding during the peak of the dry season when probable low moisture content of foods and high daytime temperatures might be disadvantageous. However, there was no relationship between season of birth and infant mortality.     

Grooming in brown howler monkeys,Alouatta fusca

The grooming behavior of a group of brown howler monkeys was studied for one year in an Atlantic forest reserve of southeastern Brazil. A total of 290 grooming bouts were recorded and analyzed. The two adult females directed most of the grooming (91%), while the adult male was the major recipient (37%). Grooming between females, and between them and their siblings, also occurred quite often. On average, the group spent 2% of its daily time grooming, with a higher frequency around noon. There were significant differences, however, in time spent grooming between seasons; grooming was more abundant during the coldest seasons (autumn–winter) and rarer in hotter ones (spring–summer). A significant negative correlation was found between grooming time and temperature, but contrary to expectations, grooming time failed to correlate with both the group' diet and the demands of food-gathering, as measured by travelling time and day range length. A comparison of grooming behavior with other species of the genus suggests that brown, red (A. seniculus), and black howler monkeys (A. caraya) are more similar to each other than to mantled howlers (A. palliata), a result that probably is linked with the differing social structure and group size of the latter species. © 1995 Wiley-Liss, Inc.     

Predation by jaguar on howler monkeys (Alouatta seniculus) in Venezuela

We document the loss of all but the youngest member of a troop of six howler monkeys due to probable jaguar predation during a 7-month period in 1988. The formation of Guri Lake resulted in forest fragmentation which forced monkeys into new and unfamiliar areas and altered the balance of predator and prey populations, and may thus have contributed indirectly to the success of the jaguar. The selection of defoliated (dead) trees for sleeping sites by the howlers may have directly increased the risk of predation. © 1992 Wiley-Liss, Inc.     

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

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

Survey of the black howler monkey,<Emphasis Type="Italic">Alouatta pigra</Emphasis>, population at the Mayan site of Palenque,Chiapas, Mexico

A survey of the population of the black howler monkey (Alouatta pigra) present at the Mayan site of Palenque was conducted during 2000. A total of 911 man/hours, spread over 112 days were spent surveying the 600 ha area of pristine forest at the site for howler troops. We detected the presence of 136 individuals of which 131 were members of 20 troops, the rest were 3 solitary adult males and 2 adult males travelling as a pair. Ecological density was estimated at 23 individuals/km². Mean troop size was 7.0 individuals and it ranged from 2–12 individuals; 60% of the troops were multimale. All sighting of howler monkeys were in evergreen rain forest and 75% were in trees ≥20 m in height. The reported densities and mean troop size are higher than those reported for the species in Guatemala and in central Quintana Roo, Mexico. The vegetation of the forest contains tree species reported to be used by species ofAlouatta in the Moraceae, Sapotaceae, Leguminosae, and Lauraceae plant families. Protection of a large perimeter area (ca 1700 ha) around the archeological site by the Mexican government ensures the conservation of the forest and of the black howler monkey population present at the site.     

Prenatal dental development in the black howler monkey (Alouatta caraya)

Prenatal dental development was investigated in 19 black howler monkey fetuses that ranged in crown-rump length from 84 mm to 170.5 mm. During this period of fetal development, all of the deciduous teeth and the first permanent molars were found to pass through various stages of crown and root formation. The deciduous incisors, canines, and first molars each calcified from a single calcification center. The second deciduous molars each calcified from two separate calcification centers. And, the third deciduous and first permanent molars each calcified from four separate calcification centers. The morphogenetic events involved in the establishment of the molar crown patterns were found to differ markedly from those of their counterparts among catarrhine primates. In all cases, however, the calcification sequence was found to be directly related to the morphology of the developing crown.     

Seed predation ofCariniana estrellensis (Lecythidaceae) by black howler monkeys,Alouatta caraya

Seed predation by howler monkeys is poorly documented. Here we report the seed predation onCariniana estrellensis (Lecythidaceae) fruits by the black howler monkeyAlouatta caraya in south-east Brazil during an intense dry season. This observation suggests that even non-specialized seed predators such as howlers can use seeds in critical periods of dry season.     

Tool use by a red howler monkey (Alouatta seniculus) towards a two-toed sloth (Choloepus didactylus)

Among New World monkeys, spontaneous tool use and object manipulation are commonly descirbed inCebus species only. We report here an occurrence of tool manipulation by a wild male red howler monkey (Alouatta seniculus), observed using a stick to softly but repeatedly hit a two toed sloth (Choloepus didactylus) resting in the same tree. The ecological context of this unusual behavior for this quiet species generally showing very little manipulative propensity is discussed.     

Histological and microbiological aspects of the vagina in captive howler monkeys (Alouatta caraya)

The histology and the glycogen content of the vaginal epithelium was studied in 15 adultAlouatta caraya monkeys. The histological sections revealed a thin epithelium without cornification. The application of the PAS-amylase method showed absence of glycogen. The microbial flora of the vagina was examined in eight adultAlouatta caraya. The vaginal smears showed a mixed flora with a predominance of Gram+cocci. Haemolytic streptococci were found in 100% of the tested monkeys. Other cocci, such asStaphylococcus albus, Streptococcus faecalis andMicrococcus sp. were less frequent. Of the fecal organisms,Proteus sp. was the most frequently isolated. Neither ureaplasms nor any species ofLactobacillus could be isolated. Positive cultures for nonpathogenic yeasts was a common feature. The relation between the absence of glycogen in the vaginal epithelium and the impossibility to isolate lactobacilli is discussed.     

A new southern limit for the distribution ofAlouatta caraya in Rio Grande do Sul State,Brazil

The discovery of two groups of the black howler monkey,Alouatta caraya, inhabiting two orchards on a cattle farm, Fazenda Casa Branca (29°56′S, 55°59′W), Rio Grande do Sul State, Brazil, represents a new southern limit for the geographic distribution of this species.     

Squirrel monkey cytomegalovirus antibodies in free-ranging black howler monkeys (Alouatta caraya), Misiones, Argentina

Serum from four black howler monkeys (Alouatta caraya) was screened for antibodies to seven viruses by dot immunoassay. Cytomegalovirus antibodies were detected in three of four individuals and provide the first evidence of exposure by black howler monkeys to this virus.     

Diet of the red howler monkey (Alouatta seniculus) in French Guiana

We report the feeding behavior and food preferences of a troop of red howler monkeys (Alouatta seniculus) over two annual cycles in primary tropical rain forest in French Guiana. The monkeys used 195 plant species from 47 families as food. Major food categories were young leaves (54%), mature fruits (21.5%), and flowers (12.6%). Other food categories included old leaves, immature fruits, termitarium soil, bark, and moss. The monkeys were less selective than other howler groups, since 19 plant species contributed 1% to their diet and accounted for only 35.7% of their total diet. The Sapotaceae was the most frequently eaten plant family and represented >10% of the total diet.     

Prometaphase chromosomes of the howler monkey (Aloutta caraya): G,C, NOR,and restriction enzyme (RES) banding

Prometaphase lymphocyte chromosomes from eight adult argentinian Alouatta caraya females were characterized using sequential G-C banding techniques, Ag-NOR bands and bands obtained with the restriction enzymes Hae III, Eco RI, Alu I and Sau 3A. The cytogenetic analysis showed 2n = 52, with four, five, or six NOR chromosomes. Digestion with Hae III and Eco RI produced G-like-bands. Centromere regions and two interstitial C-bands (in chromosomes number 16 and 21) showed intraindividual or interindividual heterochromatic polymorphisms. Alu I digestion produced C-like bands with gaps in the centromere regions, and Sau 3A produced C-like bands. The karyotypes and banding patterns of A. caraya, A. palliata, A. belzebul, and A. seniculus are compared, based on whole chromosome and whole arm homeologies. © 1994 Wiley-Liss, Inc.