Use of sleeping trees by ursine colobus monkeys (Colobus vellerosus) demonstrates the importance of nearby food

Examination of the characteristics and locations of sleeping sites helps to document the social and ecological pressures acting on animals. We investigated sleeping tree choice for four groups of Colobus vellerosus, an arboreal folivore, on 298 nights at the Boabeng-Fiema Monkey Sanctuary, Ghana using five non-mutually exclusive hypotheses: predation avoidance, access to food, range and resource defense, thermoregulation, and a null hypothesis of random selection. C. vellerosus utilized 31 tree species as sleeping sites and the species used differed per group depending on their availability. Groups used multiple sleeping sites and minimized their travel costs by selecting trees near feeding areas. The percentage that a food species was fed upon annually was correlated with the use of that species as a sleeping tree. Ninety percent of the sleeping trees were in a phenophase with colobus food items. Entire groups slept in non-food trees on only one night. These data strongly support the access to food hypothesis. Range and resource defense was also important to sleeping site choice. Groups slept in exclusively used areas of their home range more often than expected, but when other groups were spotted on the edge of the core area, focal groups approached the intruders, behaved aggressively, and slept close to them, seemingly to prevent an incursion into their core range. However, by sleeping high in the canopy, in large, emergent trees with dense foliage, positioning themselves away from the main trunk on medium-sized branches, and by showing low rates of site reuse, C. vellerosus also appeared to be avoiding predation in their sleeping site choices. Groups left their sleep sites later after cooler nights but did not show behavioral thermoregulation, such as huddling. This study suggests that access to food, range and resource defense, and predation avoidance were more important considerations in sleeping site selection than thermoregulation for ursine colobus.     

Spider monkey sleeping sites: Use and availability

The behavior of spider monkeys (Ateles geoffroyi) at sleeping sites and the characteristics of these sites were studied in Santa Rosa National Park, Costa Rica. The spider monkeys tended to congregate just prior to dusk at a number of sleeping sites which were repeatedly used (81.6%), but occasionally they slept in trees which were only used once (18.4%). All of the regularly used sleeping trees were not used concurrently, but rather, there was a rotation between sites. In general, males were not encountered at regularly used sleeping sites as often as other age/sex classes, and when they were in all male subgroups, they did not sleep in repeatedly used sites. The trees used as regular sleeping sites tended to be large, but such trees were common in the group's home range. The size of the subgroups attending repeatedly used sleeping trees was large when food was abundant and small when food was scarce. It is suggested that this relationship reflects that the costs of travelling to the sleeping site would be more easily recovered when food was abundant than when food was scarce.     

Sleeping Sites of <Emphasis Type="Italic">Rhinopithecus brelichi</Emphasis> at Yangaoping,Guizhou

Arboreal primates spend about half of their lives at sleeping sites; hence, selection of sleeping sites is crucial for individual survival, and data concerning them is important for conservation efforts. We collected data on sleeping sites for a group of the endangered snub-nosed monkey (Rhinopithecus brelichi) at Yangaoping (27°58′N, 108°45′E) from January 2006 to December 2007. All sleeping sites were located in the mid-slope and in the shadow of ridges facing the northeast and southeast. The monkeys remained quiet while entering and occupying sleeping sites, and slept in evergreen species during the cold season (December–March). Trees in sleeping sites were similar in height and girth at breast height to those elsewhere, but some trees in lower areas were larger. The monkeys usually slept in close proximity to the last feeding spot, and their daily activities usually occurred around the sleeping site. Areas adjacent to sleeping sites were used more intensively than those not adjacent. Monkeys left the sleeping sites later in the morning in the cold season. These behavioral responses suggested that predation risk, thermoregulation, and climate stresses are the main determining factors in the selection of sleeping sites for this temperate monkey.     

Strategies used by bonnet macaques (Macaca radiata) to reduce predation risk while sleeping

Sleep results in a decrease in alertness, which increases an animal’s vulnerability to predation. Therefore, choice of sleeping sites would be predicted to incorporate predator-avoidance strategies. The current study, conducted in two national parks in southern India, examined the behaviors adopted by bonnet macaques (Macaca radiata) to reduce the risk of being preyed upon while sleeping. Bonnet macaques from an urban setting with a low predatory risk were included for comparison. The physical characteristics of the sleeping sites in the forest corresponded with features that were most difficult for predators to access; bonnet macaques selected emergent trees with high boles near human settlements. These trees typically overhung water. Within the canopy, individuals slept in huddled subgroups near the terminal ends of branches, preferentially selecting branches over water. Subgroups were generally composed of members of the same age and sex, which likely promoted social bonding. Adult males and females with infants selected branches higher than members of other age and sex categories. The lateral distances of individuals along branches from the main trunk were similar across demographic categories. The size of a subgroup appeared to be limited by the weight a branch could support; lateral distances were maintained by regulation of mean subgroup weight, with heavier individuals forming smaller subgroups. The urban troop slept on the top of a building. Subgroup compositions at the urban site were similar to those at the forest sites. However, subgroup size, not restricted by branch fragility, resulted in larger subgroups than those found in the forest. Our results indicate that bonnet macaques adopted a suite of behaviors that reduced their risk of being preyed upon at night by selecting sleeping sites that minimized predator encounters and by selecting the safest locations within the canopy.     

Sleeping Tree Selection of Cao Vit Gibbon (Nomascus nasutus) Living in Degraded Karst Forest in Bangliang,Jingxi, China

We studied the sleep‐related behavior of two Cao Vit gibbon (Nomascus nasutus) groups in Bangliang Nature Reserve in Jingxi County, China between January 2008 and December 2009 to test four hypotheses related to sleeping tree selection (predation avoidance, thermoregulation, food access, and range defense). Gibbons entered sleeping trees 88 ± SD 37 min before sunset before their main potential nocturnal predator become active. They usually moved rapidly and straight to sleeping trees and kept silent once settled. Over the course of the study, gibbon groups used many (87 and 57 per group) sleeping trees and reused them irregularly. They also tended to sleep in relatively tall trees without lianas, choosing small branches close to the treetop. These behaviors would make it difficult for potential terrestrial predators to detect and approach the gibbons. Therefore, these results strongly support the predation avoidance hypothesis. Gibbons tended to sleep closer to ridges than to valley bottoms and they did not sleep at lower elevations in colder months. They thus appeared not to select sleeping trees to minimize thermoregulatory stress. Gibbons very rarely slept in feeding trees, instead generally sleeping more than 100 m away from the last feeding trees of the day or the first feeding tree of the next morning. These patterns led us to reject the food access hypothesis. Lastly, we did not find evidence to support the range defense hypothesis because gibbons did not sleep in overlap areas with neighbors more often than expected based on the proportion of overlap and exclusively used areas. Am. J. Primatol. 74:998‐1005, 2012. © 2012 Wiley Periodicals, Inc.     

Effects of water level on sleeping-site selection and inter-group association in proboscis monkeys: why do they sleep alone inland on flooded days?

A one-male group (BE-Group) of proboscis monkeys was studied along the Menanggul River, a tributary of the Kinabatangan River, Sabah, Malaysia, from May 2005 to 2006. It has generally been assumed that proboscis monkeys only set up their sleeping sites along the riverbank; however, when more than 1 m of water covered the forest floor for more than 700 m inland from the riverbank during the seasonal flood, the BE-Group slept inside the forest. It seems that the sleeping-site selection of the BE-Group was not influenced by food availability during the flooded months because the food availability by the vegetational survey did not vary much between flooded and non-flooded months. In addition, feeding behaviors of the focal monkey in the BE-Group also did not vary much between flooded and non-flooded days. On the other hand, the water level statistically influenced the sleeping-site selection. The proboscis monkeys remained in inland forest during the flooded days because of the reduced predation threat, as terrestrial predators such as clouded leopards are prevented from foraging by deep water covering the forest floor. On non-flooded days when the BE-Group slept at the riverbank, they frequently slept close to other one-male groups on the riverside trees. Contrastingly, when the group slept inside the forest on flooded days when the water level was high, they slept away from other groups. This difference in the need for one-male groups to sleep close to each other might be attributed to the decreased predation threat during high water level in the flooded days.     

Sleeping site selection and presleep behavior in wild pigtailed macaques

Several factors are likely to control sleeping site selection and presleep behavior in nonhuman primates, including predation risk and location of food resources. We examined the effects of these factors on the sleeping behavior of northern pigtailed macaques (Macaca leonina). While following a troop living in the surroundings of the Visitor Center of Khao Yai National Park (Thailand), we recorded the physical characteristics and location of each sleeping site, tree, the individuals' place in the tree, posture, and behavior. We collected data for 154 nights between April 2009 and November 2010. The monkeys preferred tall sleeping trees (20.9 ± SD 4.9 m) and high sleeping places (15.8 ± SD 4.3 m), which may be an antipredator strategy. The choice of sleeping trees close to the last (146.7 ± SD 167.9 m) or to the first (150.4 ± SD 113.0 m) feeding tree of the day may save energy and decrease predation risk when monkeys are searching for food. Similarly, the choice of sleeping sites close to human settlements eases the access to human food during periods of fruit scarcity. Finally, the temporal pattern of use of sleeping sites, with a preference for four of the sleeping sites but few reuses during consecutive nights, may be a trade‐off between the need to have several sleeping sites (decreasing detection by predators and travel costs to feeding sites), and the need to sleep in well‐known sites (guaranteeing a faster escape in case of predator attack). Am. J. Primatol. 73:1222–1230, 2011. © 2011 Wiley Periodicals, Inc.     

Predicting the Competitive Regime of Female <Emphasis Type="Italic">Colobus vellerosus</Emphasis> from the Distribution of Food Resources

We examined the spatial and temporal distribution of the foods of ursine colobus (Colobus vellerosus) at Boabeng-Fiema, Ghana as a means to predict the monopolizablity and usurpability of their food resources. Recent evidence suggests that food may not be limiting for folivorous primates, and that male sexual coercion may be a more important influence on folivore social organization. To address the question, we collected focal data on the feeding behavior of adult females and males over 11 mo (September 2000-August 2001) on 2 groups: WW (n = 31–33 individuals) and B (n = 8–16 individuals). We also conducted phenological monitoring and a tree survey of the two-group home ranges to establish food availability and distribution. We used 2 behavioral or organism-defined indicators of feeding behavior to assess potential resource contestability: food site residence time and distance moved between food sites. The colobus fed on a high diversity of species, most of their food trees were not clumped in distribution, within-tree interfood distances were short, and food trees were large. The only condition associated with the potential for monopolization was low food tree density. However, low food tree density may be offset by the colobus’ use of large trees. Taken together, the ecological and behavioral indicators suggest the food resources of Colobus vellerosus had a low potential for monopolization. Our results also indicate mature leaves had the longest food site residence time, which may suggest they should be the most usurpable plant part, though their presumed low quality and high abundance probably counteracted the effect. The pattern implied the potential for direct feeding competition among Colobus vellerosus at Boabeng-Fiema was low and agonistic interactions over food are not expected. Instead, a group size effect on feeding efficiency should be a more predominant influence on feeding efficiency, if food is limiting for the species.     

Multiple Ecological Factors Influence the Location of Proboscis Monkey (<Emphasis Type="Italic">Nasalis larvatus</Emphasis>) Sleeping Sites in West Kalimantan,Indonesia

Multiple ecological factors have been hypothesized to influence primate sleeping site selection. Testing multiple hypotheses about sleeping site selection permits examination of the relative strength of distinct ecological factors and expands our ability to understand how selection pressures influence primate sleeping behavior. Here we examine how avoidance of biting insects, thermoregulation, foraging efficiency, tree stability, and interspecific competition influence selection of sleeping sites by proboscis monkeys (Nasalis larvatus) in Indonesian Borneo. We collected data on relative insect abundance, temperature, rainfall, food availability, group size, sleeping site location, and presence of other primates for 12 mo. Using formal model comparison and information criteria, we analyzed the relative importance of these ecological factors in determining one aspect of sleeping site location: distance from the river. Our models supported the avoidance of biting insects and the foraging efficiency hypotheses. Proboscis monkeys slept further inland on nights when the abundance of sandflies was high along the river, and when less food was available along the river. Many studies suggest that primates select sleeping trees and locations to reduce predation risk; our study indicates that additional factors may also be important in determining sleeping site selection.     

Constraints on Group Size in Red Colobus and Red-tailed Guenons: Examining the Generality of the Ecological Constraints Model

The ecological constraints model proposes that an increase in group size will increase intragroup feeding competition and thereby constrain group size. Although this model has received wide acceptance, tests of it are based only on a few studies of species that have similar ecological requirements and social organizations, and there are reasons to question the widespread acceptance of the assumptions underpinning it. Via a 2-year study, we explored determinants of group size in species that feed on markedly different types of foods: the folivorous red colobus (Procolobus pennantii) and the frugivorous/insectivorous red-tailed guenon (Cercopithecus ascanius). We established 4 study sites approximately 15 km apart in Kibale National Park, Uganda, to examine the relationship between average group size and food availability. In both species, we quantified interdemic variation in diet, density of food trees, rate of travel, and group size. Red colobus at all sites relied heavily on leaf resources (75.5%–86.9%), but fruit (6.4%–13.9%) and flowers (2.0%–13.9%) were important in some populations. In general, red-tailed guenons fed on fruit (35.7%–59.7%), insects (14.5%–17.6%), and young leaves (12.2%–32.8%), but the amount of time allocated to these foods varied among sites. Average monthly density of trees bearing food items ranged among sites from 45 to 79 trees/ha for red colobus and from 19.6 to 67.3 trees/ha for red-tailed guenons. For both species, rate of travel was similar among sites, with one exception for red colobus. Average red colobus group size varied among sites from 14 to 40 (28 groups counted). Red-tailed guenon group size varied among sites from 11 to 24 (16 groups counted). As predicted by the ecological constraints model, group size increased with food tree density across sites for both species.     

Sleeping Site Selection by Urban Marmosets (<Emphasis Type="BoldItalic">Callithrix penicillata</Emphasis>) Under Conditions of Exceptionally High Predator Density

Domestic cats are known to kill small mammals and birds, and represent a predatory threat to all small wildlife. We investigated whether a high cat density affects the choice of sleeping sites of urban marmosets (Callithrix penicillata). One group of marmosets and ≥115 domestic cats live in an 18-ha area in the Municipal Park of Belo Horizonte City, Minas Gerais, Brazil. We observed the selection of 105 consecutive sleeping sites by the marmosets between January and April, 2009. We observed predation of 3 juvenile marmosets by domestic cats and a mean of 3.24 attempted predation events per day. The park contains 3777 trees of 275 species, but the marmosets chose only 6 different species —3 palms, 2 eucalyptuses, and 1 fig— and a total of 12 different sleeping trees. Sleeping sites appeared to be chosen to minimize the risk of cat predation. Marmosets slept only in tall trees (mean±SD = 22.49 m ± 5.4) with high first branches (mean above-ground level = 10.36 m ± 4.7) and smooth or thorny bark. Marmosets reached sleeping trees from adjacent trees, and neither marmosets nor cats climbed into sleeping trees from the ground. These results suggest that domestic cat predation pressure influences the physical characteristics of marmoset sleeping site selection, e.g., height, to reduce predation rate.     

Spawning migrations in the monogamous butterflyfish,Chaetodon trifasciatus

Spawning and related behavior of a monogamous butterflyfish,Chaetodon trifasciatus, were observed at Kuroshima Island, Okinawa, Japan. Each heterosexual pair defended a feeding territory in the daytime. Spawning occurred at dusk on the days around full or new moon in the daytime. Spawning occurred at dusk on the days around full or new moon in the vicinity of offshore tidal currents. Spawning migration to such sites occurred in pairs, the feeding territories of which were located in areas of inshore currents. In the evening each pair established a small temporary territory, which they spawned adjacent to and slept within until the next morning. The distribution of sleeping sites as well as tidal current directions may determine the spawning sites of this butterflyfish.     

Use of sleeping sites by a titi group (<Emphasis Type="Italic">Callicebus coimbrai</Emphasis>) in the Brazilian Atlantic Forest

Predation pressure affects most aspects of primate behaviour, and is especially pronounced in the context of the use of sleeping sites, given the vulnerability of the animal at this time. Most small-bodied platyrrhines have highly systematic patterns of sleeping site choice and use. This study analyses the use of sleeping sites by a free-ranging group of titis (Callicebus coimbrai) monitored at a site in Sergipe, Brazil, between July, 2009 and June, 2010. When the subjects approached a sleeping tree their behaviour was typically cautious, including slow and silent movement, early retirement (20–162 min before sunset on 52 dry afternoons), and sleeping in a tight huddle with their tails entwined. Despite this behaviour, which has an obvious anti-predator function, the group slept in only three different trees during the course of the study, and returned to the same tree used on the previous night on a quarter of evenings (n = 56). This was despite the availability within the group’s home range of a large number of trees with similar structural characteristics (i.e. tall, open crown in the upper canopy). Surprisingly, the three trees were all members of the same species, Licania littoralis (Chrysobalanaceae). The choice of this species, which was not an important source of dietary resources, and the repeated use of a small number of sites, did not seem to be related to factors such as ranging or foraging patterns, but may have a been a response to the specific threat from capuchins, Cebus xanthosternos.     

Sleeping site preferences in tufted capuchin monkeys (Cebus apella nigritus)

The characteristics and availability of the sleeping sites used by a group of 27 tufted capuchin monkeys (Cebus apella nigritus) were studied during 17 months at the Iguazu National Park, Argentina. We tested different hypotheses regarding possible ultimate causes of sleeping-site selection. Most sleeping sites were located in areas of tall, mature forest. Of the 34 sleeping sites the monkeys used during 203 nights, five were more frequently used than the others (more than 20 times each, constituting 67% of the nights). Four species of tree (Peltophorum dubium, Parapiptadenia rigida, Copaifera langsdorfii and Cordia trichotoma) were the most frequently used. They constituted 82% of all the trees used, though they represent only 12% of the trees within the monkeys' home range which had a diameter at breast height (DBH) > 48.16 cm (1 SD below the mean DBH of sleeping trees). The sleeping trees share a set of characteristics not found in other trees: they are tall emergent (mean height +/- SD = 31.1+/-5.2 m) with large DBH (78.5+/-30.3 cm), they have large crown diameter (14+/-5.5 m), and they have many horizontal branches and forks. Adult females usually slept with their kin and infants, while peripheral adult males sometimes slept alone in nearby trees. We reject parasite avoidance as an adaptive explanation for the pattern of sleeping site use. Our results and those from other studies suggest that predation avoidance is a predominant factor driving sleeping site preferences. The patterns of aggregation at night and the preference for trees with low probability of shedding branches suggest that social preferences and safety from falling during windy nights may also affect sleeping tree selection. The importance of other factors, such as seeking comfort and maintaining group cohesion, was not supported by our results. Other capuchin populations show different sleeping habits which can be explained by differences in forest structure and by demographic differences.     

Selection of sleeping trees in pileated gibbons (Hylobates pileatus)

Selection and use patterns of sleeping sites in nonhuman primates are suggested to have multiple functions, such as predation avoidance, but they might be further affected by range defense as well as foraging constraints or other factors. Here, we investigate sleeping tree selection by the male and female members of one group of pileated gibbons (Hylobates pileatus) at Khao Ang Rue Nai Wildlife Sanctuary, Thailand. Data were collected on 113 nights, between September 2006 and January 2009, yielding data on 201 sleeping tree choices (107 by the female and 94 by the male) and on the characteristics of 71 individual sleeping trees. Each sleeping tree and all trees ≥40 cm diameter at breast height (DBH) in the home range were assessed (height, DBH, canopy structure, liana load) and mapped using a GPS. The gibbons preferentially selected tall (mean=38.5 m), emergent trees without lianas. The majority of the sleeping trees (53.5%) were used only once and consecutive reuse was rare (9.5%). Sleeping trees were closer to the last feeding tree of the evening than to the first feeding tree in the morning, and sleeping trees were located in the overlap areas with neighbors less often than expected based on time spent in these areas. These results suggest avoidance of predators as the main factor influencing sleeping tree selection in pileated gibbons. However, other non‐mutually exclusive factors may be involved as well. Am. J. Primatol. 72:617–625, 2010. © 2010 Wiley‐Liss, Inc.     

Antipredation Sleeping Behavior of Skywalker Hoolock Gibbons (<Emphasis Type="Italic">Hoolock tianxing</Emphasis>) in Mt. Gaoligong,Yunnan, China

Studying sleeping behavior can provide key information for understanding the ecology of a species. Antipredation is an important factor that affects primate sleeping behavior. We studied antipredation sleeping behavior in skywalker hoolock gibbons (Hoolock tianxing). We studied one group (NA) and a solitary female (NB) at Nankang from July 2010 to September 2011, and another group (BB) at Banchang from May 2013 to December 2014 in Mt. Gaoligong, Yunnan, China. Over the study period, we recorded 67 sleeping trees for members of group NA over 92 days, 17 trees for the solitary female NB over 22 days, and 159 trees for members of group BB over 186 days. Skywalker hoolock gibbons at both sites rarely used the same tree on consecutive days (N = 3 at both sites). They traveled fast to enter sleeping tree a mean of 160 ± SD 43 min before sunset at Nankang, and a mean of 192 ± SD 40 min before sunset at Banchang. They seldom (Nankang: 14%, N = 183 observations; Banchang: 25%, N = 548 observations) defecated in sleeping trees. They slept at sites with more tall and large trees and preferred to sleep on tall trees in the site. They slept on branches of small diameter and closer to tree tops. Our study suggests that antipredation plays an important role in skywalker hoolock gibbons’ sleeping tree selection and sleeping behavior. In addition, our data suggest potential effects of habitat degradation on gibbons’ sleeping behavior. Tall trees are especially important for gibbons in degraded forest and should be protected.     

Sleeping site selection of Francois’s langur (<Emphasis Type="Italic">Trachypithecus francoisi</Emphasis>) in two habitats in Mayanghe National Nature Reserve,Guizhou, China

Sleeping site selection is an important aspect of the behavioral biology of primates. Comparison of different habitats for the same species in this context enhances understanding of their adaptation to altered environments. We collected data on sleep-related behaviors for 6 groups of Francois’s langur (Trachypithecus francoisi) in two habitats, in Mayanghe National Nature Reserve, Guizhou, China. Regardless of habitat, all sleeping sites were located in areas of steep terrain of ≥60°. In undisturbed habitat, sleeping sites were located only in evergreen broadleaf forest with rock caves and crevices surrounded mainly by a vegetation layer of shrub + rock. In disturbed habitat, sleeping sites were also located in mixed evergreen and deciduous broadleaf forest and in grassland, including rock caves, crevices, and pits, surrounded mainly by arbor + shrub and shrub + rock. Wild food availability was higher in undisturbed habitat than disturbed habitat, but food abundance around sleeping sites was lower. Water sources included river and seasonal gully or pond. There was strong positive correlation between use of sleeping sites away from the river valley and occurrence of seasonal water sources. The number of sleeping sites varied across groups, numbering 6, 7, and 10 for three specific groups. Few sleeping sites were used all year round. Six consecutive nights was the longest recorded run. Francois’s langurs’ sleeping habits differed between two habitats. In undisturbed habitat, minimizing predation risk appeared to predominate, expressed by choosing steep terrain, open visual field, and inconspicuous presleeping behavior. In disturbed habitat, along with predation avoidance, food resources may strongly influence sleeping site selection, as demonstrated by the richer food abundance and greater foraging activity around the site. Finally, water resources may influence choice of sites distant from the river; such sites were used less frequently during water shortages.     

Sleeping cluster patterns and retiring behaviors during winter in a free-ranging band of the Sichuan snub-nosed monkey

Little information is available on the sleeping cluster pattern and retiring behavior of Sichuan snub-nosed monkeys (Rhinopithecus roxellana). Here, we provide observational data on a provisioned free-ranging band in the Qinling Mountains, central China. The results suggest that winter night activity of R. roxellana is a compromise between antipredator and thermoregulatory strategies and an adaptation to ecological conditions of their temperate habitat. Monkeys retired between 1804 and 1858 h in winter. In support of the antipredation hypothesis, all monkeys slept in trees at night, whereas 18.8% of individuals slept on the ground during the day. Also, the study band was more spatially cohesive at night than in daytime, with shorter distances between one-male units. Keeping warm is critical for survival in freezing temperatures. Monkeys often slept in the lower stratum of the tree canopy, avoiding the upper canopy where it is cold and windy. They formed larger sleeping clusters at night than in daytime. The most common types of night-sleeping clusters were adult females and juveniles, followed by adult females with other adult females. These accounted for 60.2% of the total records. The frequency of female–male clusters is two times greater, and that of adult male–juvenile clusters was four times less at night than during the day. The variations in composition of sleeping clusters suggest affiliative patterns at night-sleeping sites differ from those during the day.     

Multiple central place foraging by spider monkeys: travel consequences of using many sleeping sites

Summary Central place foraging models assume that animals return to a single central place such as a nest, burrow, or sleeping site. Many animals, however choose between one of a limited number of central places. Such animals can be considered Multiple Central Place Foragers (MCPF), and such a strategy could reduce overall travel costs, if the forager selected a sleeping site close to current feeding areas. We examined the selection of sleeping sites (central places) by a community of spider monkeys (Ateles geoffroyi) in Santa Rosa National Park, Costa Rica in relation to the location of their feeding areas. Spider monkeys repeatedly used 11 sleeping trees, and they tended to choose the sleeping site closest to their current feeding area. A comparison of the observed travel distances with distances predicted for a MCPF strategy, a single central place strategy, and a strategy of randomly selecting sleeping sites demonstrated (1) that the MCPF strategy entailed the lowest travel costs, and (2) that the observed travel distance was best predicted by the MCPF strategy. Deviations between the observed distance travelled and the values predicted by the MCPF model increased after a feeding site had been used for several days. This appears to result from animals sampling their home range to locate new feeding sites.     

Night observations of free-ranging Rhesus monkeys

The nocturnal distribution and behavior of individually marked Macaca mulatta were studied at the La Parguera, Puerto Rico, colony of the Caribbean Primate Research Center. The new image intensifier was used successfully to identify 399 monkeys in 185 sleeping clusters. Monkeys moved into mangrove trees close to favorite feeding areas usually 35 minutes after sunset. The group condensed to less than one-half the daytime spread, vocalizations increased and grooming ceased. Movements and vocalizations ceased several hours after sunset, although bursts of activity occurred throughout the night. Activity resumed 40 minutes before sunrise. Activity was higher during full moon, when I observed feeding, play and sexual behavior. Fights at night were twice as frequent during the breeding season. Monkeys slept in clusters of one to four, 58% of which were of two. Sixty-three percent were composed of maternal relatives, 33% were mother-infant pairs. Mature males clustered with non-related males, slept alone or with females (in the breeding season). Yearlings slept with their mothers or with older siblings. Distribution of monkeys in a group at night reflects daytime associations.