A bibliography on howler monkeys (Alouatta sp.)

Reports dealing with howler monkeys since1900 have been assembled in the present bibliography. The references marked with(R) have been taken verbatim from Ruch's Bibliographia Primatologica. Papers identified by^* deal more extensively withAlouatta.     

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.     

A phylogeny of howler monkeys (Cebidae: Alouatta) based on mitochondrial, chromosomal and morphological data

The current taxonomic status of the species and subspecies belonging to the genus Alouatta is addressed by combined phylogenetic analysis using morphological, kariotipyc and molecular data (mitochondrial genes cytocrome oxidase II and cytochrome B). Our result demonstrated that Alouatta palliata is the most basal taxon for the genus in concordance with previous studies, as well as showing the validity of the taxon Alouatta sara as a species. Also our analysis shows that the sex chromosome has evolved from a XY/XX system to a X1X2Y1Y2/X1X1X2X2 system within the genus, as well as an increase in the size and complexity of the hioideal bone.     

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.     

Adoption in free-ranging red howler monkeys,Alouatta seniculus of Venezuela

This report describes three cases of infant adoption in red howler monkeys (Alouatta seniculus) of Venezuela. In one case, a lactating female adopted her infant granddaughter after the infant's mother disappeared and the infant survived for the next 25 months. In the second case, an adult female adopted her infant granddaughter for nine days while the infant's mother was still a group member. In the third case, a nulliparous female temporarily adopted an infant from a neighboring group. The details and the possible reasons for these adoption are described.     

Attitudes towards urban howler monkeys (Alouatta caraya) in Paraguay

Primates - Increasing urbanisation is encroaching into natural habitats and sometimes forcing wildlife into urban centres. Whether or not wildlife can thrive in an urban environment is dependent on...     

Roaring rhythms in black howler monkeys (Alouatta pigra) of Belize

Roaring was recorded during 15-min intervals for 55 days from April 29 to July 14, 1981 in the area around Bermuda Landing, Belize. Roaring profiles were compiled to represent four three-week periods in which roaring was graphed against the time of day. Rates of roaring were also calculated for three troops. Results indicate a gradual change in the daily profile of roaring from dry to rainy season. The marked bimodality of roaring at dawn and dusk in the dry season changed to a more dampened bimodality with reduced dawn and dusk peaks and more roaring during the midday in the rainy season. This seems related to the decreased hours of sun and the amount of rain during the wet season. Additionally, literature on monkeys with long range vocalizations suggests that bimodal peaks in calling may be more prevalent in species which display territorial defense.     

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.     

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.     

Genetic diversity in black howler monkeys (Alouatta pigra) from Belize

To assess the level of genetic variation in a threatened black howler monkey (Alouatta pigra) population, we examined 36 allozyme loci and restriction fragment profiles of mitochondrial DNA (mtDNA). Mean heterozygosity at allozyme loci was only 0.021 and 5.6 percent of the loci were polymorphic. Analyses of mtDNA also revealed low genetic diversity compared with other primates. F-statistics revealed no significant genetic heterogeneity among troops within the Bermudian Landing preserve, but did indicate a deficiency of heterozygotes at one of the two loci. We explore several explanations for this result, which is unexpected in a socially structured primate. Low genetic diversity in this population may reflect its history of demographic bottlenecks. Am. J. Phys. Anthropol. 102:329–336, 1997. © 1997 Wiley-Liss, Inc.     

Artificial nest predation by brown howler monkeys (Alouatta guariba clamitans)

Howler monkeys (Alouatta spp.) have long been considered strongly vegetarian primates. Their occasional ingestion of invertebrates has largely been interpreted as unintentional. Recent observations of the consumption of bird eggs by Alouatta caraya living in small and resource-impoverished habitat patches in the state of Rio Grande do Sul (RS), Brazil help to confirm that such behavior by howler monkeys is at times intentional. We report the findings of an experimental study on artificial nest predation by free-ranging Alouatta guariba clamitans in RS and third-party unpublished observations of intentional feeding on animal matter by Alouatta arctoidea in Venezuela and Alouatta palliata in Mexico. A nest station composed of ten artificial nests baited daily with two quail eggs each was placed at six study sites. Each site was monitored from dawn to dusk during 10–12 consecutive days. Individuals (juvenile males and an adult female) from two of the six study groups inspected the nests and ate eggs once. Study subjects from these two groups were the only ones to be supplemented with food (basically fruit) by local inhabitants, a habit that may have decreased their level of neophobia and facilitated their visit to the artificial nests. We suggest that faunivory is an opportunistic and infrequent, but intentional howler monkey feeding behavior.     

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.     

Dispersal patterns in black howler monkeys (Alouatta pigra): Integrating multiyear demographic and molecular data

Dispersal is a fundamental process in the functioning of animal societies as it regulates the degree to which closely related individuals are spatially concentrated. A species’ dispersal pattern can be complex as it emerges from individuals’ decisions shaped by the cost–benefit tradeoffs associated with either remaining in the natal group or dispersing. Given the potential complexity, combining long-term demographic information with molecular data can provide important insights into dispersal patterns of a species. Based on a 15-year study that integrates multiyear demographic data on six groups with longitudinal and cross-sectional genetic sampling of 20 groups (N = 169 individuals, N = 21 polymorphic microsatellite loci), we describe the various dispersal strategies of male and female black howler monkeys (Alouatta pigra) inhabiting Palenque National Park, Mexico. Genetically confirmed dispersal events (N = 21 of 59 males; N = 6 of 65 females) together with spatial autocorrelation analyses revealed that the dispersal pattern of black howlers is bisexual with strong sex-biases in both dispersal rate (males disperse more often than females) and dispersal distance (females disperse farther than males). Observational and genetic data confirm that both males and females can successfully immigrate into established groups, as well as form new groups with other dispersing individuals. Additionally, both males and females may disperse singly, as well as in pairs, and both may also disperse secondarily. Overall, our findings suggest multiple dispersal trajectories for black howler males and females, and longer multiyear studies are needed to unravel which demographic, ecological and social factors underlie individuals’ decisions about whether to disperse and which dispersal options to take.     

Molecular phylogenetics of large-bodied tamarins, Saguinus spp. (Primates, Platyrrhini)

With 33 recognized taxa, the tamarins, Saguinus spp., constitute the most diverse genus of New World monkeys (Platyrrhini), and are found almost exclusively within the Amazon basin. This diversity can be subdivided into three main morphological groups, based primarily on pelage characteristics, although there is also an ecologically important division between the small- and large-bodied forms (adult body weight ± 300 g vs. > 450 g, respectively). In the present study, the phylogenetic relationships among the large-bodied forms were analysed using the sequences of a fragment of the mitochondrial rRNA16S gene, from which 58 informative sites were identified. The analysis revealed the existence of four main lineages, three of which coincided with geographical and/or morphological patterns. However, Saguinus leucopus formed a highly distinct clade, contradicting expectations based on its morphology and distribution, but corroborating a previous study of the NADH dehydrogenase subunit I (ND1) gene. Whereas genetic differences between some closely related species were relatively small (< 1%), that observed between the two specimens of S. imperator was twice higher (± 2%), indicating the possible presence of distinct species within this taxon. Previous molecular clock analysis suggested that the earliest radiation event of the large-bodied tamarins occurred sometime in the lower Miocene, whereas the most recent events, such as the division of the closely related S. midas and S. niger would have occurred during the Pleistocene. Most of these events would thus have taken place before the formation of the present-day river system, which now constitutes a considerable barrier to gene flow among many populations.     

Collection and evaluation of semen from captive howler monkeys (Alouatta caraya)

Semen samples (n=58) were collected by electroejaculation from nine adult male howler monkeys (Alouatta caraya) between November 2000 and August 2001 at the National Primates Center, Ananindeua, Brazil. The ejaculates were free of coagulum. Mean (+/-S.D.) values were: volume, 0.09 +/- 0.05 ml; pH, 8.1 +/- 0.5; concentration 649.5 +/- 926.7 x 10(6) sperm/ml; progressive motility, 75.8 +/- 18.1%; forward progressive sperm motility (scale, 0-5), 3.5 +/- 1.0; live spermatozoa, 68.3 +/- 15.0%; primary defects, 9.6 +/- 4.5%; and secondary defects, 11.8 +/- 4.6%. There were high correlations between motility and live sperm (r = 0.91, P < 0.01), motility and forward progressive sperm motility (r = 0.84, P < 0.01) and between forward progressive sperm motility and live sperm (r = 0.78, P < 0.01). There were no alterations observed during clinical examinations and hematological analysis performed before and after semen collection. Therefore, the method was considered safe and efficient. It can be used for the evaluation of the breeding potential of male howler monkeys in captivity and for the establishment of new assisted reproductive technology (ART) for threatened species of neotropical primates.