Mandible/basihyal relationships in red howler monkeys (Alouatta seniculus): A craniometrical approach

The morphological relationships between the cranium and basihyal of red howler monkeys (Alouatta seniculus) were analyzed based on measurements of 36 cranial and 3 basihyal dimensions and observations of the female specimen in spirits. In this study, 115 crania from 111 red howler monkeys and 4 mantled howler monkeys (Alouatta palliata) were used. The analyses from the standpoints of the correlation coefficients, principal component analysis, discriminant function analysis, age changes and sex differences were performed and the following results were obtained: (1) The cranial measurements closely related to the basihyal measurements were mandibular length, occipital breadth, facial length, ramus height, cranial base length, bigonial breadth and pr-i length. (2) Age changes for the mandibular measurements in males of red howler monkeys were remarkable, and, in particular, the development of the gonion toward posterior and lateral directions were characteristic. (3) The largest sex differences were found in the mandibular measurements of red howler monkeys among the Anthropoidea of seven genera compared. (4) The existence of a “cline” in the cranial measurements of the red howler monkey was recognized. (5) The inter-species differences in the crania between the red howler monkey and mantled howler monkey are obvious, metrically and non-metrically. Based on the results mentioned above, the morphological relationships between the mandible and basihyal in the red howler monkey are discussed.     

Noninvasive collection of fresh hairs from free‐ranging howler monkeys for DNA extraction

The use of noninvasive collected samples as source of DNA in studies of wild primate populations has increased in recent years. Fresh‐plucked hairs represent an important source of DNA, with relatively high quality and concentration. In this study, we describe a low‐cost noninvasive technique for collecting fresh‐plucked hairs used to obtain DNA samples from free‐ranging black howler monkey populations (Alouatta pigra). We designed and manufactured darts made of wooden dowels, with the anterior part smeared with glue, which were projected with blowpipes to trap howler monkey hairs. All of the materials to make the darts are inexpensive and are available locally. We collected 89 samples from 76 individuals residing in 15 troops, and the total number of hairs obtained was 754. We found no differences in the number of hairs collected among sex–age classes or among localities but the percentage of darts recovered with sample varied among localities. Preliminary results indicate that over 96% of samples yielded DNA suitable for polymerase chain reaction‐based microsatellite marker analysis. The technique proved successful for collecting fresh‐plucked hairs of free‐ranging black howler monkeys without any trauma to the animals and can be easily adapted to obtain samples from other wild primate and mammal species. Am. J. Primatol. 71:359–363, 2009. © 2009 Wiley‐Liss, Inc.     

Timing of births in sympatric brown howler monkeys (Alouatta fusca clamitans) and northern muriquis (Brachyteles arachnoides hypoxanthus).

We monitored the birth patterns of sympatric brown howler monkeys (Alouatta fusca clamitans) and northern muriquis (Brachyteles arachnoides hypoxanthus) during a 4‐yr period from October 1996 to August 2000 at the Estação Biológica de Caratinga, Minas Gerais, Brazil. Brown howler monkey births (n = 34) occurred throughout the year, and birth frequencies did not differ between rainy and dry season months. The aseasonal birth patterns of the howler monkeys differed significantly from the dry season concentration and dry month peak in muriqui births (n = 23). We found no effects of infant sex or the number of females on interbirth intervals (IBIs) in our 10 howler monkey study troops. IBIs of brown howler monkeys averaged 21.2 ± 2.5 mo (n = 8, median = 21.0 mo), and were significantly shorter following dry season births than rainy season births. Their IBIs and yearling survivorship (74%) were similar to those reported for other species of howler monkeys, but yearling survivorship was much lower than that of muriquis (94%), whose IBIs were more than 12 mo longer than those of the howler monkeys. Our study extends comparative knowledge of birth patterns in Alouatta to a poorly known species, and provides insights into the different ways in which diet and life history may affect the timing of births in large‐bodied platyrrhines under the same seasonal ecological conditions. Am. J. Primatol. 55:87–100, 2001. © 2001 Wiley‐Liss, Inc.     

Dispersión Primaria de Semillas por Primates y Dispersión Secundaria por Escarabajos Coprófagos en Tikal,Guatemala1

We linked primary dispersal by spider monkeys (Ateles geoffroyi) and howler monkeys (Alouatta pigra) to post‐dispersal seed fate by studying the effects of dung type and defecation pattern on secondary seed dispersal by dung beetles. First, we described the defecation patterns for both primate species. Howler monkeys generally defecated in groups (88% of observed defecations), with each individual producing on average 31 g of dung, resulting in a large area of the forest floor (31 m²) covered by large amounts of dung (clumped spatial pattern). Spider monkeys generally (96% of observed defecations) defecated individually, each individual producing an average of 11 g of dung, resulting in a small area of the forest floor (2 m²) covered by small amounts of dung (scattered spatial pattern). Secondly, we captured dung beetles using as bait the dung of both primate species, to detect differences in the assemblages of these secondary seed dispersers attracted to the dung of both primates. More individual dung beetles, but not more species, were attracted to howler monkey dung than to spider monkey dung. Finally, we assessed experimentally (using plastic beads as seed mimics) how dung type (Ateles vs. Alouatta) and defecation pattern (scattered vs. clumped) affect secondary seed dispersal by dung beetles. We found that post‐dispersal seed fate was affected by dung type, with more seeds being buried when present in howler monkey dung, than in spider monkey dung, but was not affected by defecation pattern. It is important to consider post‐dispersal processes, such as secondary seed dispersal by dung beetles, when comparing species of primary dispersers.     

In situ hybridization (FISH) maps chromosomal homologies between Alouatta belzebul (Platyrrhini,Cebidae) and other primates and reveals extensive interchromosomal rearrangements between howler monkey genomes

We hybridized whole human chromosome specific probes to metaphases of the black-and-red howler monkey Alouatta belzebul in order to establish chromosomal homology between humans and black-and-red howlers. The results show that the black-and-red howler monkey has a highly rearranged genome and that the human chromosome homologs are often fragmented and translocated. The number of hybridization signals we obtained per haploid set was 40. Nine human chromosome probes gave multiple signals on different howler chromosomes, showing that their synteny is disturbed in A. Belzebul. Fourteen black-and-red howler autosomes were completely hybridized by one human autosomal paint, six had two signals, three had three signals, and one chromosome had four signals. Howler chromosomes with multiple signals have produced 12 chromosomal syntenies or hybridization associations which differ from those found in humans: 1/2, 2/20, 3/21, 4/15, 4/16, 5/7, 5/11, 8/18, 9/12, 10/16, 14/15, and 15/22. The hybridization pattern was then compared with those found in two red howler taxa and other mammals. The comparison shows that even within the genus Alouatta numerous interchromosomal rearrangements differentiate each taxa: A. belzebul has six unique apomorphic associations, A. seniculus sara and A. seniculus arctoidea share seven derived associations, and additionally A. seniculus sara has four apomorphic associations and A. seniculus arctoideaseven apomorphic associations. A. belzebul appears to have a more conserved karyotype than the red howlers. Both red and black-and-red howlers are characterized by Y-autosome translocations; the peculiar chromosomal sex system found in the red howler taxa could be considered a further transformation of the A. belzebul sex system. The finding that apparently morphologically similar or even identical taxa have such extreme genomic differences has important implications for speciation theory and neotropical primate conservation. Am. J. Primatol. 46:119–133, 1998. © 1998 Wiley-Liss, Inc.     

Impact of yellow fever outbreaks on two howler monkey species (Alouatta guariba clamitans and A. caraya) in Misiones,Argentina

Two yellow fever outbreaks (YFOs) ocurred in northeastern Argentina between November 2007 and October 2008, seriously affecting populations of two howler monkey species: the brown howler Alouatta guariba clamitans and the black howler Alouatta caraya. Both howlers live syntopically in El Piñalito Provincial Park, Misiones, where four groups (36 individuals) were studied since January 2005. The first dead howlers were found on January 20, 2008, in El Piñalito. Systematic searches found 14 dead howlers within the area (12 from the study groups and two from neighboring groups), with only two young seen on January 25, 2008, and none found since up to December 2008. In October 2008, another YFO hit howler monkey populations from El Soberbio, Misiones. Overall, 59 howlers were found dead in Misiones from November 2007 to December 2008. Thanks to the alert of the howler's death in El Piñalito, a prompt human vaccination campaign started in the area. Wild howler monkey populations from both species are in a delicate situation in Misiones, especially the brown howler, an already endangered species in Argentina and endemic to the Atlantic Forest. If we add the recurrence of YFOs to the reduction of suitable habitat to small fragments, it could be only a matter of time until howler populations disappear from the Upper Paraná Atlantic Forest in Misiones. Am. J. Primatol. 72:475–480, 2010. © 2010 Wiley‐Liss, Inc.     

Micro‐computed tomographic evaluation of fetal skeletal changes induced by all‐trans‐retinoic acid in rats and rabbits

BACKGROUND: Our laboratory has been conducting positive control studies to evaluate the utility of micro‐computed tomography (micro‐CT) for qualitative evaluation of fetal skeletal morphology. All‐trans‐retinoic acid (atRA) was used to produce a different spectrum of defects compared to our previous studies with boric acid and hydroxyurea. METHODS: Groups of five mated Crl:CD(SD) female rats each were administered vehicle or atRA (2.5–50 mg/kg) on GD 10, and groups of four mated Dutch Belted rabbits each were dosed with vehicle or atRA (6.25–25 mg/kg) on GD 9. Cesarean sections were performed on GD 21 and 28, respectively. Following external examination the viscera were removed and fetuses scanned in a micro‐CT imaging system. Fetuses were subsequently stained with alizarin red. Skeletal morphology was evaluated by each method without the knowledge of treatment group. Total bone mineral content (BMC) of each fetus was quantitated using the micro‐CT images. RESULTS: In rats there were dose‐related increases in the incidence of extra lumbar vertebra and non‐dose‐related increases in supernumerary ribs at all dose levels. There were decreases in mean number of ossified sacrocaudal vertebra at ≥5 mg/kg, and increases in skull bone malformations at ≥10 mg/kg. Rabbits were less sensitive on a mg/kg basis since skeletal malformations and a decrease in mean number of ossified sacrocaudal vertebra were observed only in the 25‐mg/kg group. Micro‐CT evaluation detected essentially the same incidence of skeletal abnormalities as seen in alizarin red‐stained rat and rabbit fetuses. BMC analysis showed a trend toward slight decreases in atRA‐treated rats, but no notable changes in rabbits. CONCLUSIONS: These results add support to our previous work that demonstrates that micro‐CT imaging can effectively assess rat and rabbit fetal skeletal morphology. Birth Defects Res (Part B) 89:408–417, 2010. © 2010 Wiley‐Liss, Inc.     

Capture of Alouatta guariba clamitans for the surveillance of sylvatic yellow fever and zoonotic malaria: Which is the best strategy in the tropical Atlantic Forest?

Howler monkey capture is an arduous and expensive task requiring trained and specialized professionals. We compared strategies and methods to most efficiently capture Alouatta guariba clamitans in remnants of the Atlantic Forest in Rio de Janeiro and its bordering states of Minas Gerais and São Paulo. We tested whether or not the success of expeditions in the forest with anesthetic darts, nets, and baited traps differed with and without the support of an information network, a contact chain built with key institutions and inhabitants to continuously monitor howler monkey presence. The influence of forest conditions (vegetation type and fragment size) upon darting success was also evaluated. We captured 24 free‐living A. guariba clamitans. No howler monkey was caught with traps, probably due to the predominantly folivore feeding to high local plant diversity providing a great variety of food options. Captures based on an information network were significantly more efficient in terms of numbers of caught monkeys than without it. Captures with darts were considerably more efficient when performed in semideciduous forests and small forest fragments as opposed to ombrophilous forests or large woods. Although we walked great distances within the forest searching for howler monkeys, all but one animal were captured at the forest fringes. Hindrances to search and the darting method in the Atlantic Forest, for example, the steep terrain, high tree canopies, hunt pressure, and low A. guariba clamitans population density, were mitigated with the use of the information network in this monkey capture. Moreover, the information network enhanced the surveillance of zoonotic diseases, which howler monkeys and other nonhuman primates are reservoirs in Brazil, such as malaria and yellow fever.     

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.     

Successional loss of two key food tree species best explains decline in group size of Panamanian howler monkeys (Alouatta palliata)

Negative impacts of discrete, short‐term disturbances to wildlife populations are well‐documented. The consequences of more gradual environmental change are less apparent and harder to study because they play out over longer periods and are often indirect in their action. Yet, they can drive the decline of wildlife populations even in seemingly pristine and currently well‐protected habitats. One such environmental change is a successional shift in a community's species composition as it regenerates from disturbance caused by past human land use. Early and middle successional tree species often provide key foods to folivores and frugivores, but the abundance of these resources drops as the forest matures, with adverse repercussions for these consumers. Our 44‐year record (1974–2018) of howler monkey (Alouatta palliata) group sizes and demographic composition from Barro Colorado Island, Panama, a protected reserve, documents an example of this phenomenon. After 70 years of relative stability, the mean size of howler monkey groups exhibited a marked decline, beginning in 2003. This downward trajectory in group size has continued through the most recent census in 2018. The composition of howler groups also changed significantly during the study period, with the patterns of decline differing among age/sex classes. There is no evidence that these changes were caused by increased rates of emigration, group fission, predation, parasitism, or disease. Rather, they are best explained by an island‐wide, succession‐driven decline in the densities of two species of free‐standing fig trees, Ficus yoponensis and F. insipida, which together were providing ~36% of BCI howlers’ annual diet. Abstract in Spanish is available with online material.     

Survey of Alouatta caraya, the black-and-gold howler monkey, and Alouatta guariba clamitans, the brown howler monkey, in a contact zone, State of Rio Grande do Sul, Brazil: evidence for hybridization

Sympatry and natural hybridization between howler monkey taxa (Alouatta spp.) has only recently being confirmed in the wild. Surveys in areas of potential contact between the distribution of two taxa have shown that sympatry is rare, although more common than previously known. Here we report the results of a survey conducted in a contact zone between the only two sexually dichromatic howler monkey taxa, Alouatta caraya and A. guariba clamitans, in São Francisco de Assis, State of Rio Grande do Sul, Brazil. Our survey, covering an area of about 400 ha at the Cerro dos Negros (29°33′50″–29°35′10″S, 54°58′40″–54°59′50″W; ~100–279 m a.s.l.), was successful in locating seven black-and-gold and one brown howler monkey social groups living syntopically. Black-and-gold group size ranged from 5 to 15 individuals, whereas the brown group was composed of 7 individuals. The pelage color of three adult males belonging to different black-and-gold groups and another adult male belonging to the brown howler group presented a mosaic of red or rufous and black. These adult males and an adult female living in another black-and-gold group are putative hybrids. Therefore, it appears that pre-zygotic reproductive isolation has not evolved, at least not completely, between these howler monkey species, corroborating previous reports for these and other Alouatta taxa. Future genetic studies need to confirm the occurrence of hybridization in this contact zone, and to determine the viability and fertility of hybrids and their possible offspring. In addition, there is no evidence supporting the existence of significant segregation in habitat and resource utilization by black-and-gold and brown howler monkeys.     

Interactions between tayras (<Emphasis Type="Italic">Eira barbara</Emphasis>) and red-handed howlers (<Emphasis Type="Italic">Alouatta belzebul</Emphasis>) in eastern Amazonia

Two tayras (Eira barbara) were observed attacking an infant red-handed howler (Alouatta belzebul) on an island in eastern Brazilian Amazonia, as a nearby adult male watched passively. In a separate incident, four tayras were seen attacking a subadult female on the ground. Tayras were also observed in the vicinity of the two howler study groups on a number of occasions over a 9-month period. During this same period, the two groups lost a third of their members, including infants and subadults, and the remains of six animals were found at the study site. While tayras were the only predators seen attacking the howlers, it remains unclear to what extent they were responsible for apparently high mortality rates in this high-density, isolated howler population.     

Spatio–temporal Variations in Post‐dispersal Seed Fate1

The post‐dispersal fate of Chrysophyllum lucentifolium (a canopy tree; Sapotaceae) seeds was analyzed in French Guiana over three consecutive years. Experiments using 750 thread‐marked seeds were performed to investigate seed removal, predation, and caching by terrestrial vertebrates on howler monkey (Alouatta seniculus) defecation sites, where clumps of intact C. lucentifolium seeds were observed. Year‐to‐year variations in seed fate during the peak fruiting period were considered in relation to overall fruit and seed resource availability estimated by a raked‐trail survey. The effect of two forest areas, which differed in soil and floristic composition, was examined with conspecific fruiting tree density as a covariant. Exclosure versus open treatment was used to discriminate small rodents (not larger than a spiny rat) from other vertebrates. The presence of fresh howler dung did not affect seed fate after 20 days as shown by comparisons between defecation sites and control during the first year. There was a significant effect of year on the percentage of seeds remaining after 20 days. Low seed removal in 1995 and 1996 (compared to 1997) corresponded to higher overall fruiting and higher fruiting of C. lucentifolium, or the presence of alternative resources for rodents. An effect of forest area was observed on the seed removal rate, which varied with years and protection. Comparatively, an effect of forest area on the percentage of seeds lost was observed in 1996 and an effect of treatment on the percentage of seeds eaten was seen in 1995. The mode of seed caching suggested that spiny rats were the main seed remover. Results of this study suggest that greater seedling recruitment may occur when large fruit crop and high howler dispersal co‐occur with a lower impact of rodents (i.e., when rodents are saturated by abundant and diversified fruit resources such as in 1995). Such event synchrony, however, is highly unpredictable after only three years of study.     

Interspecific Infanticide and Infant‐Directed Aggression by Spider Monkeys (Ateles hybridus) in a Fragmented Forest in Colombia

Interspecific aggression amongst nonhuman primates is rarely observed and has been mostly related to scenarios of resource competition. Interspecific infanticide is even rarer, and both the ultimate and proximate socio‐ecological factors explaining this behavior are still unclear. We report two cases of interspecific infanticide and five cases of interspecific infant‐directed aggression occurring in a well‐habituated primate community living in a fragmented landscape in Colombia. All cases were initiated by male brown spider monkeys (Ateles hybridus) and were directed toward infants of either red howler monkeys (Alouatta seniculus: n = 6 cases) or white‐fronted capuchins (Cebus albifrons: n = 1 case). One individual, a subadult spider monkey male, was involved in all but one case of interspecific infanticide or aggression. Other adult spider monkeys participated in interspecific aggression that did not escalate into potentially lethal encounters. We suggest that competition for food resources and space in a primate community living in high population densities and restricted to a forest fragment of ca. 65 ha might partly be driving the observed patterns of interspecific aggression. On the other hand, the fact that all but one case of interspecific infanticide and aggression involved the only subadult male spider monkey suggests this behavior might either be pathological or constitute a particular case of redirected aggression. Even if the underlying principles behind interspecific aggression and infanticide are poorly understood, they represent an important factor influencing the demographic trends of the primate community at this study site. Am. J. Primatol. 74:990‐997, 2012. © 2012 Wiley Periodicals, Inc.     

Birth in free-ranging howler monkeysAlouatta seniculus

This report describes two live births in the red howler monkey (Alouatta seniculus) at Hato Masaguaral, Venezuela. Both births took place during the afternoon on a limb of a tree. An adult troop male was next to the females during delivery. Supported by the Environmental Science Program Grant to Dr. J. F.Eisenberg.     

Williams-Beuren mapping in Callithrix argentata, Callicebus cupreus and Alouatta caraya indicates different patterns of chromosomal rearrangements in neotropical primates

Human chromosome 7 has a complex syntenic origin. It was divided into two segments in both the ancestral primate karyotype and in Platyrrhini. Apparently, a small segment in the ancestral platyrrhine karyotype was associated with HSA5 and the remainder formed a middle‐sized submetacentric. We tested the dynamics of platyrrhine chromosomes by hybridizing the locus specific Willams‐Beuren probe (7q 11.23, 450 kb) to chromosomes of representative species from the three families of the New World monkeys recently proposed by molecular genomics: Cebidae, Callithrix argentata (bare ear marmoset or silvery marmoset, 2n = 44); Pitheciidae, Callicebus cupreus [red titi monkey, or coppery monkey, 2n = 46)] and Atelidae, Alouatta caraya (black and gold howler, 2n = 52). In both the marmoset and the howler monkeys, the signal was found on the small segment of chromosome 7 associated with human chromosome 5, but not in Callicebus cupreus. Instead, the Williams‐Beuren syndrome (WS) signal was found on a C. cupreus chromosome previously reported to be hybridized only by human chromosome 1. The WS probe indicates a small, but complex translocation never described before. Our results point out that fluorescence in situ hybridization (FISH) with locus specific probes and cloned DNA fragments such as bacterial aftificial chromosomes (BACs) provides higher resolution than FISH with whole chromosomes paints. It may be well that the variability seen in the hybridization patterns and revealed by the WS FISH in this report is as a result of a rearrangement ‘hot spot’. The WS region in humans is composed of region‐specific different blocks of complex segmental duplications that probably promote the extraordinary rate of evolutionary dynamics of this region among primate species, and which continues to be reflected today by the predisposition of this region to disease syndromes such as WS. The evolutionary history of this region also suggests that repeat families in this region had their origin in a common ancestor of both Old World and New World monkeys.     

Sex differences in leadership during group movement in mantled howler monkeys (Alouatta palliata)

Benefits of group life depend in large part on whether animals remain cohesive, which often requires collective decisions about where and when to move. During a group movement, the leader may be considered as the individual occupying the vanguard position of the group progression, when its movement evokes following by other group members. In nondespotic societies, individuals with greater incentives to move frequently are leaders. During 15 months of observations (1,712 contact hours), we investigated two mantled howler monkey (Alouatta palliata) groups at La Flor de Catemaco (Los Tuxtlas, Mexico) to examine whether sex and female reproductive state influenced leadership likelihood in two contexts: movements toward feeding trees; movements associated with loud calls, a group-defense behavior used by males of this genus. Females led and occupied forward positions during group movements toward feeding trees more often than adult males. Adult females led these movements more frequently when they were gestating than when they were lactating or cycling. There were no differences between sexes in the leadership of group movements associated with loud calls. Leadership by gestating females is perhaps the result of their higher nutritional/energetic needs when compared with cycling females, and of their greater mobility when compared with lactating females carrying dependent offspring. Female leadership during movements toward feeding trees may be a mechanism to optimize access to food resources in mantled howler monkeys.     

The Identity Objection to the future‐like‐ours argument

Some critics of Don Marquis's ‘future‐like‐ours’ anti‐abortion argument launch what has been called the Identity Objection. The upshot of this objection is that under a psychological theory of personal identity, a non‐sentient fetus lacks precisely what Marquis believes gives it a right to life – a future like ours. However, Eric Vogelstein, in a recent article, has argued that under this theory of personal identity a non‐sentient fetus, in fact, has a future like ours, which he believes dissolves the Identity Objection. But Vogelstein is mistaken. Even if he is correct that there is a sense in which a non‐sentient fetus has a future of value under a psychological theory of personal identity, the sense in which it has one is importantly different from the sense in which we have one, meaning that, under such a theory, a non‐sentient fetus does not have a future like ours.     

Interspecific interaction and predator avoidance behavior in response to tayra (<Emphasis Type="Italic">Eira barbara</Emphasis>) by mantled howler monkeys (<Emphasis Type="Italic">Alouatta palliata</Emphasis>)

This paper reports the response of one howler monkey group (Alouatta palliata) to a group of potential predators, the tayra (Eira barbara). The apparently successful predator avoidance behavior of the monkeys was recorded in detail. We observed a group of four adult tayras moving around theAlouatta group displaying a species-typical aggressive behavioral pattern. The two adult females of the howler group successfully chased the tayras away by repeatedly moving closer to the mustelids and even following them until the predators moved off.     

Howling on the edge: Mantled howler monkey (Alouatta palliata) howling behaviour and anthropogenic edge effects in a fragmented tropical rainforest in Costa Rica

The function of long calling is a subject of interest across animal behaviour study, particularly within primatology. Many primate species have male‐specific long‐distance calls, including platyrrhines like the folivorous howler monkey (Alouatta spp.). Howler monkeys may howl to defend resources such as feeding trees or areas of rich vegetation from other monkey groups. This study tests the ecological resource defence hypothesis for howling behaviour in the mantled howler monkey (Alouatta palliata) and investigates how anthropogenic forest fragmentation may influence howling behaviour. More specifically, this study examines how howling bout rate, duration, precursors and tree species richness, DBH, and canopy cover vary in 100 m anthropogenic edge and interior forest zones at La Suerte Biological Research Station (LSBRS), a fragmented tropical rainforest in Costa Rica. Results show that tree species richness and canopy cover are higher in forest interior at this site, suggesting that monkeys should howl at greater rates in the interior to defend access to these higher‐quality vegetation resources. Overall, our results supported the ecological resource defence hypothesis. The main howl precursor was howling from neighbouring groups. Although howling rate did not differ between forest zones, howling bouts from forest interior were longer, had a greater number of howls per bout and were preceded by different precursors than howls from anthropogenic edge zones, including more howls from neighbouring groups. Our findings provide some of the first evidence for behavioural edge effects in primate vocal communication behaviour.