Census habitat preference and polyspecific associations of six monkeys in the Lomako Forest Zaire.код для вставкиСкачать
American Journal of Primatology 34295-307 (1994) RESEARCH ARTICLE Census, Habitat Preference, and Polyspecific Associations of Six Monkeys in the Lomako Forest, Zaire SCOTT MCGRAW Department of Anthropology, State University of New York at Stony Brook, Stony Brook This paper reports preliminary data on a number of poorly known cercopithecids inhabiting the Lomako Forest, Zaire. Data include those on density, biomass, group size, the relationship between group type (mono vs. polyspecific) and forest type (mixed primary, secondary, monodominant primary, and swamp), and vertical stratification. Species examined are Colobus angolensis, Cercocebus aterrimus, Cercopithecus wolfi, Cercopithecus ascanius, Cercopithecus neglectus, and Allenopithecus nigroviridis. The density and biomass for the Lomako Forest anthropoids (excluding Cercopithecus neglectus and A. nigroviridis) are 165 ind/km2 and 1,034 kg/km2, respectively. Cercopithecus wolfi and Colobus angolensis are found in group sizes similar to those reported from other sites while Cercopithecus ascanius, Cercocebus aterrimus, and A. nigroviridis display group sizes unique to the Lomako. While Colobus angolensis, Cercocebus aterrimus, Cercopithecus ascanius and Cercopithecus wolfi were found, to varying extents, in all four forest types, Cercopithecus neglectus and A. nigroviridis inhabited only swamp forest. The different species sort out along vertical continua both within and between the four forest types. 0 1994 Wiley-Liss, Inc. Key words: Cercopithecus, Allempithecus, Colobus, Cercocebus, ecology and polyspecific associations INTRODUCTION Zaire is the most primate-rich country in Africa, with at least 24 anthropoid and 8 prosimian species in 14 genera [Oates, 19851. Despite this extraordinary diversity, few studies on monkey communities have been carried out in Zaire as most field work on the cercopithecids of equatorial Africa has been conducted in sites east (e.g., Uganda, Tanzania, Kenya) or west (e.g., Gabon, Cameroon, Nigeria, Ivory Coast) of the Congo basin. Long-term research on African monkeys is rare and even basic information such as relative abundance and patterns of habitat use are lacking for many taxa. In this paper, preliminary ecological data on a number of poorly known cercopithecids living in the Lomako Forest, Zaire are placed in the context of data from other field sites (see Table I for summary of data from previous studies). Gautier-Hion et al. [19811 have suggested that the formaReceived for publication May 28, 1993; revision accepted March 9, 1994. Address reprint requests to Scott McGraw c/o Dr. Randall Susman, Department of Anatomical Sciences, School of Medicine, State University of New York a t Stony Brook, Stony Brook, NY 11794-8081. 0 1994 Wiley-Liss, Inc. 296 I McGraw TABLE I. Comparative Data on Lomako Forest Monkeys* x Body weight Species (kd Group size Colobus angolensis 9.9 6.6 Population density (ind/km2) 7.7 Groves [19731 Moreno-Black & Maples [19771 4.3 4.9 5.5 Cercocebus aterrimus Cercopithecus wolfi Cercopithecus ascanius Cercopithecus neglectus 8 17.5 69 Horn  3.8 ND ND Thomas 119911 3.6 22, 23, 24 72 Cords  17-23 30-35 117 140 5,6 28 5.5 *ND = 4.5 Struhsaker & Leland [19791 Quiris  Brennan [19851 Gautier-Hion & Gautier [19781 3.2 Allenopithecus nigroviridis References Thomas  > 40 ND Gautier [19851 no data. Body weights are averages of adult males and females. tion of mixed-species groups within different forest types may be a response to (among other things) varying risks of predation within each habitat. Data on the number of group types within each habitat are presented to address this issue. The species discussed are: Colobus angolensis (Angolan Black and White colobus), Cercocebus aterrimus (Black mangabey), Cercopithecus ascanius whitesidei (Redtail monkey), Cercopithecus wolfi wolfi (Wolf‘s guenon), Cercopithecus neglectus (DeBrazza’s monkey), and Allenopithecus nigroviridis (Allen’s Swamp monkey). THE STUDY SITE The Lomako Forest is located in the interior of the Congo Basin (Zaire) between the Yekokora and Lomako Rivers a t 0.50’N, 21.05’E (Fig. 1). In addition to the monkeys examined in this study, the Lomako Forest is home to a population of pygmy chimpanzees (Pan paniscus) that has been the subject of study by members of the Lomako Forest Pygmy Chimpanzee Project, based a t the State University of New York a t Stony Brook, since 1979 [see Susman, 19841. At least four gross vegetation types are found in the Lomako. (1) The majority of the primary study site consists of approximately 35 km2 of lowland terra firma forest. (2) Pockets of secondary growth that include sites of former hunting villages, manioc fields, and tree fall gaps are scattered throughout the terra firma forest. (3) Areas of monodominant slope forest, comprised almost exclusively of Gilbertiodendron dewevrei trees, crosscut the site along streams that feed the Lomako River. (4) Finally, the primary study site is bordered by extensive areas of permanently inundated swamp forest that encroach into the evergreen forest via stream flood plains (dominated by Sclesopermium manii). These vegetation types are indicated in Figure 2. Census of Lomako Forest Monkeys I 297 Fig. 1. The location of Lomako Forest within the Congo Basin. Within the terra firma forest the main canopy layer is continuous, reaching heights of between 30 and 40 m and dominated by species of Polyalthia and Scorodophloeus (e.g., Polyalthia suaueolens, Scorodophloeus zenkeri, Dialium zenkeri, Zruingia robur, Celtis mildbraedi, Crudia laurentii). Emergent trees (e.g., Oxystigma oxyphyllum and Antiaris toxicaria) are common and may reach heights of up to 55 m. The under story is more discontinuous and consists of a network of lianes which allows for movement between forest layers. The lowest herbaceous layer, consisting largely of Haumania liebrechtsiana and Palisota spp., usually reaches heights no greater than 4 m [Malenky & Stiles, 19911. Further details on the study site may be found in Susman et al. [19801, White [19861, and Malenky [19901. METHODS Results presented here are from a 2-month study conducted in 1991. Twentyfour surveys were conducted along established trails and fruit transects in the primary study site. Although the use of existing pathways may bias density estimates, artificial transects were not cut within the Lomako Forest so as not to disturb the existing habitat. Sections of the trail system which curved more than 30" were excluded to avoid inadvertently recording animals twice which may have been flushed farther along the transect routes. Three trails were censused eight times each. Transect lengths were 5.1, 5.5, and 3 km, respectively (see Fig. 2 for location of transects). All surveys began at 6:OO A.M. and were concluded by approximately 12:OO noon. On census days, trails were walked slowly and all observations were made from the transect path only. Every attempt was made not to violate the 298 I McGraw Fig. 2. Transect routes and major forest types found within the Lomako Forest study site. assumptions of line transect sampling discussed by Burnham et al. : i.e., (1) that monkeys directly on the transect were never missed, (2) that monkeys were fixed a t the initial sighting location and none were counted twice, (3) that distances were measured exactly (estimated to the nearest meter), and (4)that sightings were independent events. After Rodman , the following data were collected a t all localities: (1)time of sighting, (2) location on transect, (3) forest type, (4) distance to first animal detected, (5) species present, (6) group type (mono- or poly-specific; various definitions of poly-specific associations have been employed by other workers [e.g., Bernstein et al., 1976; Waser, 1986a; Cords, 1987; Mitani, 19911. In this study, I followed the rationale of Struhsaker  who recorded poly-specific associations “when two or more social groups were spatially intermingled; this usually means they are in the same or contiguous tree and within 20 m of one another” [Gartlan & Struhsaker, 1972; Struhsaker, 1975]), (7) number of animals sighted, (8) height of first animal observed, (9) activity of first animal sighted, and (10) foods consumed. Using the recommendations of the National Research Council [ 19811, transect Census of Lornako Forest Monkeys / 299 TABLE 11. Maximum Reliable Sighting Distances Used for Density Calculations Species Cercopithecus ascanius Cercopithecus wolfi Cercocebus aterrimus Colobus angolensis Sighting distance (m) N 30 36 40 45 a7 72 107 19 strip width was determined using the method of maximum reliable sighting distance. Since sighting distances used for the estimation of densities were found to vary with species, densities were calculated using taxon specific distances. These distances are presented in Table 11. Noncensus days were spent following groups and recording observations ad libitum. Upon contacting a group, I recorded (1)time of sighting, (2) forest type, (3) species present, (4) initial group count, (5) height of first animal observed, and (6) activity of first animal sighted; subsequently animals were followed for as long as possible to determine the reliability of group counts obtained from census transects. This was accomplished by comparing initial group counts with counts made a t 5-minute intervals during follows. Data collected on these days were not used for density/biomass estimates but rather to supplement data on forest preference, group size, vertical distribution, and poly-specific associations derived from transect censusing. Additional time was allotted to specifically investigate the flooded riverine forests which border the primary study site. Every fourth day, I traveled through the swamp forest via a number of routes leading to the river system, collecting data in the fashion described above. Systematic forays were made on foot along the river's smaller tributaries and some portions of the inundated forest were investigated from a canoe. It must be emphasized that the four categories of habitat are found in different proportions and that equal sampling time was not spent within each vegetation type. Therefore, figures on habitat use do not necessarily represent how much time each monkey spends in each forest type. Nevertheless, these data can give a preliminary indication of gross habitat use a s the census transects sampled a t least a portion of ail four forest types (Fig. 2). RESULTS Density, Biomass, and Group Size Estimates Results of density, biomass, and group size estimates are presented in Table 111. Data on mean group counts are derived both from census counts (when I was reasonably certain the whole group had been counted) and from non-census follows when the entire group could be counted repeatedly. Cercocebus aterrimus ( x group size = 10.9) is the most abundant monkey in the study site (73.1 ind/km2)followed by nearly equal numbers of Cercopithecus ascanius (42.8 ind/km2) and Cercopithecus wolfi (44 ind/km2)with mean group sizes of 14.7 and 10.1, respectively. Colobus angolensis (5.8 ind/km2) was encountered relatively infrequently and in smaller groups ( x group size = 5) than the above taxa. Allenopithecus nigrouiridis and Cercopithecus neglectus were never observed along transect routes and density estimates were therefore not attempted for them. It is difficult to speculate on the relative abundance of these swamp taxa without systematic investigations of the inundated forest throughout the Lomako River Basin. However, considering the limited time spent exploring their habitat and the regularity with which these 300 I McGraw TABLE 111. Group Size, Density, and Biomass Estimates* Taxon Cercocebus aterrimus Colobus angolensis Cercopithecus ascanius Cercopithecus wolfi Cercopithecus neglectus Allenopithecus nigrouiridis Pan paniscus X X Total observations Group counts Group size" Group sizeb Density (indikm2) Body weight 146 77 10.9 10.2 73.1 8d 585 27 21 5 5 5.8 9.9" 57 105 24 14.7 12.7 42.8 3.6" 154 101 37 10.1 12 44.2 3.8" 168 12 5 3 ND - 5.5 7 3 4 ND - 4.5 NA NA NA ND 2' Total 165 indikm' 35 Biomass 70 1,034 *NA = not applicable; ND = no data. Tombined census and noncensus data bCensus data only. 'Badrian & Malenky [19841. dTervuren Museum (n = 4). 'Thomas [19911. monkeys were either observed or heard, it is probable that these two species are fairly common throughout the Lomako River system. Group Types and Forest Use Within the study area, the Lomako primates were not distributed evenly throughout the four categories of vegetation types and most of the Lomako monkeys displayed strong tendencies to associate with one or more different species. Table IV summarizes the relative frequency with which different group types of each species were found in different forest categories while Table V reports the composition of each mixed-species association. Cercocebus aterrimus, Cercopithecus wolfi, and Cercopithecus ascanius were most often encountered in some combination of mixed-species association. Cercocebus aterrimus was found most often in primary forest, either alone (n = 44)or in association with other taxa (n = 59). The black mangabey was encountered rarely in secondary and swamp forest while it used slope forest in proportions equal to those used by Cercopithecus ascanius and Cercopithecus wolfi. Cercopithecus ascanius and Cercopithecus wolfi were most often encountered in terra firma forest although with different frequencies. Both guenons were found in slope and swamp forest in nearly equal proportions. Mono-specific groups of Cercopithecus wolfi were observed in secondary forest only once while mono-specific groups of Cercopithecus ascanius were recorded in this vegetation type on fifteen occasions. It is interesting to note that groups comprised solely of Cercocebus aterrimus and Cercopithecus wolfi were nearly three times more common than the mixed groups of Cercocebus aterrimus and Cercopithecus ascanius. Colobus angolensis was observed a n equal number of times in primary and slope forest. This is significant because slope forest makes up only a small percentage of the total study site. It is possible that the frequency with which Colobus Census of Lomako Forest Monkeys / 301 TABLE IV. Number of Observations of Group Types in Different Forest Types 1" Species Cercocebus aterrimus Cercopithecus wolfi Cercopithecus ascanius Colobus angolensis Cercopithecus neglectus Allenopithecus nigroviridis Slope 2" Swamp Mono Poly Mono Poly Mono Poly Mono Poly 44 12 19 4 - 59 56 36 4 - 0 1 15 1 - 6 7 11 1 - 12 2 7 4 - 15 17 13 4 - - __ 7 3 1 5 12 5 3 3 3 1 0 2 TABLE V. Composition and Number of Poly-Specific Groups Polyspecific groups of two species Cercocebus aterrimus Colobus angolensis CercoDithecus ascanius Colobus angolensis Cercopithecus ascanius Cercopithecus wolfi 0 - 13 1 34 1 12 N Polyspecific groups of three species C. aterrimus, C. wolfi, and C. ascanius C. angolensis, C. wolfi, and C. ascanius C. aterrimus, C. wolfi, and C. angolensis Allenopithecus nigrouiridis, C. wolfi, and C. ascanius Polyspecific groups of four species C. aterrimus. C. ascanius. C. wolfi. and C. angolensis 26 1 2 2 5 angolensis was found in slope forest was a seasonal phenomenon as the study was conducted during the period in which Gilbertiodendron dewevrei was flowering. The preliminary data here indicate that these flowers are a preferred food of Colobus angolensis in the Lomako which may explain the high occurrence of the species in this habitat. With the exception of mono-specific groups in swamp forest, there seemed to be little association between forest and group type for Colobus angolensis. Allenopithecus nigroviridis and Cercopithecus neglectus were never observed outside of the swamp forest, although the remaining species were found in this habitat at various times and in various associations. Cercopithecus neglectus was never observed associating with other taxa while Allenopithecus nigroviridis was found in mixed groups twice. Vertical Stratification Figure 3 presents a bar graph of the height of first animal sighted with data from all four forest types pooled. Multiple comparisons among means revealed significant differences for every combination of taxa at the .01 level. A stepped series appears with Cercopithecus ascanius occupying the lowest tier followed respectively by Cercopithecus wolfi, Cercocebus aterrimus, and Colobus angolensis. In nearly 50% of all observations, Cercopithecus ascanius was observed below 10 m and was frequently seen on the ground or on low hanging lianes foraging for fallen fruit and insects. Mean height for Cercopithecus wolfi was approximately 5 m higher than that of Cercopithecus ascanius while Cercocebus aterrimus used the 302 I McGraw Cercopithecus arcaniut Cercopifhecus wolf1 Cercoeebur aterrirnut Colobus angolensis Percent observed All pairwise comparisons significant at .01 level Fig. 3. Height of first animal sighted obtained by pooling data from the four forest types. middle and upper canopy layers extensively. Although it was never observed on the ground in the course of this study, tracks of Cercocebus aterrimus were frequently found along stream beds throughout the study site and other workers in the Lomako confirm that the black mangabey does occasionally descend to the forest floor (Thompson-Handler, personal communication). Colobus angolensis was found at the greatest height of all species. The Angolan colobus was frequently seen feeding or sunning itself at the tops of emergent Gilbertiodendron dewevrei trees during the hottest parts of the day. In addition, footprints of Colobus angolensis were found along stream beds in the Lomako Forest where local guides insist the monkey digs for water worms. Both Allenopithecus nigroviridis and Cercopithecus neglectus were observed most often on the ground. Allenopithecus nigroviridis was not seen foraging above 2 m although Cercopithecus neglectus was observed feeding a t levels between 10 and 15 m above the ground. To determine whether stratification was consistent across forest types, mean height was calculated separately for each forest type (Fig. 4).(It is important to note that these heights are not scaled to those available within each forest type. This is most significant for heights recorded in secondary forest: figures reported are lower for all species in secondary forest because this habitat in the Lomako is, by definition, between 15 and 30 m shorter that the other three forest types.) In general, Colobus angolensis was consistently observed a t the upper levels of all forest types while Cercocebus aterrimus was found slightly lower. The two guenons were most often found in the mid-canopy of primary and slope forest while in swamp forest, Cercopithecus ascanius and Cercopithecus wolfi tended to frequent lower levels. DISCUSSION Information on densities and biomasses of whole African primate communities is scarce. The preliminary data presented here indicate that the density and biomass of the Lomako Forest primates are comparable to those a t other African sites. Estimates of the partial Lomako primate density (165 ind/km2) and biomass (1,034 kglkm') (excluding the swamp taxa Allenopithecus nigroviridis and Cercopithecus Census of Lomako Forest Monkeys I 303 35 30 v) & 25 + 0 n ..... E 20 n ........... c .- 2 15 Dl I".- l o L 5 0 Primary Mbau Swamp Secondary Forest Ty pe 0C. angolensis C. aterrimus C. ascanius 0C. wolfi Fig. 4. Height of first animal sighted within each forest type. neglectus) are intermediate between those reported from the Ituri (112 indlkm' and 710 kg/km2) [Thomas, 19911 and Kibale forests (549 ind/km2 and 2217 kg/km') [Struhsaker, 1975; Oates, 19771. While estimated primate densities for the Lomako fall within the range of West African sites (132-326 ind/km2),the Lomako's primate biomass is greater than that reported from any West African locality (524-761 kg/km') [Bourliere, 1985; Thomas, 19911. The Lomako estimates do not include data on the swamp taxa and it is difficult to predict how much the addition of these species would affect the total figures, since densities and group sizes for Cercopithecus neglectus and Allenopithecus nigrouiridis are believed to vary widely [see Gautier, 1985; Gautier-Hion & Gautier, 1978; Quiris, 1976; Brennan, 19851. Furthermore, because the assumptions and biases of different census methods can result in widely varying density and biomass estimates, comparisons are necessarily tentative. In general, most of the Lomako monkeys were found at individual densities and in group sizes similar to those reported from most other sites with similar taxa (see Table I). Notable exceptions include the much larger groups of Allenopithecus nigrouiridis observed by Gautier [ 19853 near Mbandaka, Zaire, the larger groups of Cercocebus aterrimus observed near Lake Tumba, Zaire [Horn, 19873, and the larger groups and higher densities of Cercopithecus ascanius reported from Kibale [Struhsaker & Leland, 19791. Despite its comparatively high density and biomass levels, the Lomako contains among the lowest number of species of any site within the Congo Basin. 304 I McGraw Seven anthropoids inhabit the Lomako while 13 are found in the Ituri Forest [Thomas, 19911, 9 at Wamba [Kano & Mulavwa, 19841, and 8 at Lake Tumba [Horn, 19871. Conspicuously absent are (1)multiple folivores (e.g., three colobines inhabit the Ituri Forest and two are found at both Wamba and Lake Tumba) and (2) multiple ground-dwelling species (e.g., five largely terrestrial species are found in Ituri Forest). These deficiencies are intriguing considering the mosaic of habitats available at the Lomako and the high productivity of the forest [Malenky, 19901. Although hunting is forbidden in the immediate study site, the monkey populations are considered threatened and it is possible that certain taxa have already been hunted to extinction [Badrian & Badrian, 19771. For example, Talapoin monkeys were never sighted in the Lomako, despite their otherwise widespread distribution south of the Zaire River [e.g., see Lernould, 19881. On the other hand, the impoverished fauna and low level of endemism might better be explained on biogeographic grounds: despite its location within the south-central forest block, the Lomako does not appear to be a n interfluvial refugium [Colyn et al., 19911. In either case, further investigation of the surrounding areas is needed to confirm the taxonomic inventory of the Lomako River Basin. To varying degrees, the monkeys show differential forest use. The most dramatic instance involves Cercopithecus neglectus and Allenopithecus nigroviridis which, despite the proximity of other forest types, were never found outside of the inundated swamp forest. Beyond the swamp forest, tendencies to use single habitats appear less marked and these data indicate that most species are capable of exploiting all vegetation types available in the Lomako. The Lomako Forest monkeys have been shown to range throughout a variety of habitats a t other locations. However, because most have not been studied in detail, the extent to which each species displays preferential habitat use is unknown. For example, in the Ituri, Thomas  noted that Colobus angolensis spent considerable time in riparian forest and was not found disproportionately in mono-dominant, Gilbertiodendron dewevrei (slope) forest. Furthermore, Colobus guereza, a close relative of the Angolan black and white colobus monkey, has been touted as a frequent user of secondary forest [Oates, 19771. Interestingly, the Lomako black and white colobus was observed in secondary forest on only two occasions. Additional time should be budgeted to investigate those factors responsible for differential habitat utilization in this and the other monkeys. Colobus angolensis, Cercocebus aterrimus, Cercopithecus ascanius, and Cercopithecus wolfi appear to occupy distinct forest levels both within and across the different forest types. In general, this paper’s findings on Colobus angolensis, Cercocebus aterrimus, and Cercopithecus ascanius concur with comparable data from other studies [Thomas, 1991; Horn, 1987; Groves, 1973; Struhsaker, 19691. While little to no information exists for Cercopithecus wolfi itself, other members of the Mona super-species (Cercopithecus mona, Cercopithecus campbelli, Cercopithecus pogonias) are known to prefer the mid and lower canopy layers [Struhsaker, 19691 which agrees with the observations contained herein. The preliminary observations on Allenopithecus nigroviridis and Cercopithecus neglectus support previous reports that these swamp taxa are semi-terrestrial [Gautier, 1985; Gautier-Hion & Gautier, 1978; Kingdon, 19881. Mixed-species groups have been reported in five of six Lomako monkeys studied at other sites [Groves, 1973; Moreno-Black & Maples, 1977; Horn, 1987; Gautier, 1985; Thomas, 1991; Cords, 1987; Gautier-Hion, 1988al. Functional explanations for poly-specific associations have most often focussed on the benefits either of increased foraging efficiency [e.g., Gautier-Hion, 1988bl or the reduction of predator pressure [e.g., Cords, 19841. While data are not yet sufficient to quantify Census of Lomako Forest Monkeys / 305 the degree of feeding competition among the Lomako monkeys, preliminary information from this and other studies suggests that there may be a high amount of dietary overlap between species [Cords, 1987; Horn, 19871. In addition, evidence is available that the Lomako monkeys are subject to significant predation pressure. The crowned hawk eagle (Stephanoaetus coronatus), a known monkey predator [Gartlan & Struhsaker, 1972; Brown, 1982; Skorupa, 19891 is common throughout the Lomako where it is known to claim monkeys of all sizes [Badrian & Malenky, 19841. Furthermore, monkeys are believed to actively avoid associating with pygmy chimpanzees [Malenky, 19901which have been implicated as monkey hunters a t other sites [Horn, 19801. It has been suggested [Gautier-Hion et al., 19811 that structural differences in vegetation types (e.g., low, dense secondary forest vs. high, open primary forest) may imply variable risks of predation from aerial (e.g., eagles) and scansorial (e.g., felids, snakes, and pygmy chimpanzees) hunters. If poly-specific groups have evolved as a response to these threats, then one might expect differential formation of poly-specific groups within each forest type. For example, that Cercopithecus wolfi was found more often in poly-specific groups in primary forest may be made possible by the mutual benefit of increased sentinels. Although such hypotheses remain speculative, one goal of future studies should be to assess the relative risks of predation within different forest types while looking for patterns in group formation among monkeys with similar amounts of dietary overlap. The mosaic of habitats found within the Lomako forest provides a good opportunity for workers interested in differential habitat use to conduct natural experiments in comparative primate biology. The data presented here (which should be viewed as preliminary) are intended to provide the basis for future studies in which particular attention should be directed toward: (a) confirming the taxonomic inventory of the broader area, (b) assessing the degree of dietary overlap among the local cercopithecids, (c) evaluating the relative risk of predation within each forest type, and (d) determining the association between group type and forest utilization. CONCLUSIONS 1. The density of the Lomako Forest anthropoids (excluding Cercopithecus neglectus and Allenopithecus nigroviridis) is estimated at 165 ind/km2 which corresponds to an overall biomass of 1,034 kg/km2.While anthropoid species richness is low (seven species), anthropoid biomass and density compare favorably with estimates from other African forests. 2. Most of the Lomako primates, for which comparable data exist, are found a t densities and in group sizes similar to those reported from other sites. Notable exceptions include smaller groups of Cercopithecus ascanius, Cercocebus aterrimus, and Allenopithecus nigroviridis in the Lomako. 3. The monkeys are not distributed randomly throughout the different forest types. While Colobus angolensis, Cercocebus aterrimus, Cercopithecus ascanius, and Cercopithecus wolfi were found, to varying extents, in all four forest types, Cercopithecus neglectus and Allenopithecus nigroviridis were never observed outside of the swamp forest. 4.The monkeys sort out vertically from one another both within and between the four forest types. In general, Colobus angolensis occupied the highest canopy layer followed by Cercocebus aterrimus, Cercopithecus wolfi, and Cercopithecus ascanius. 5 . Poly-specific associations are common in the Lomako Forest. Further atten- 306 I McGraw tion should be directed toward determining whether the formation of poly-specific groups is associated with different forest types. ACKNOWLEDGMENTS I thank Dr. Zana Ndontoni (Directeur General du CRSN), and the Centre de Recherche en Sciences Naturelle (CRSN) for permission to study in the Lomako Forest. I a m indebted to my advisor, Randall Susman, for the opportunity to work in the Lomako Forest. Helpful comments and discussions were provided by Randall Susman, John Fleagle, Charlie Janson, Richard Malenky, Nancy Thompson-Handler, Francis White, Tony Falsetti, Chris Wall, Dan Schmitt, and four anonymous reviewers. Thanks to Lucille Betti-Nash who prepared the maps. Funding for the project was furnished by NSF Grant BNS-870687 to R.L. Susman, Conservation International and the Chicago Zoological Society. REFERENCES Badrian, A.; Badrian, N. Pygmy chimpanzees. ORYX 13:463-472, 1977. Badrian, N.; Malenky, R. Feeding ecology of Pan paniscus in the Lomako Forest, Zaire. Pp. 275-299 in THE PYGMY CHIMPANZEE. R.L. Susman, ed. New York, Plenum Press, 1984. 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