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THE POPULATION AND CONSERVATION OF HOWLER MONKEYS IN VENEZUELA AND TRINIDAD Melvin Neville INTRODUCTION The demographics of a population of howler monkeys on Hato Masaguaral, a cattle ranch in Venezuela's Guarico State, is examined with regard to the practical difficulties in censusing. Extended work in limited areas with repeated age-sex counts on each troop is advocated. Census data from work in 1969-1970 and 1972 on Hato Masaguaral are analyzed to show the need for a large sample size in estimating such param- eters as sex ratio and to provide an idea of the popula- tion characteristics of howler monkeys in a protected llanos area. Hill (1962) lists five subspecies ofAlouatta seniculus for Venezuela and Trinidad. A. s. seniculus occurs on the western border with Colombia. A. s. stramineus andA, s. macconelli are found south of the Orinoco. A. s. arctoidea in the northern part of Venezuela is the nearest mainland neighbor of A. s. insulanus on Trinidad. The dominant capuchin in most of Ven- ezuela is C. nigrivittatus bruneus (see Hershkovitz, 1949; C. griseus grisens of Hill, 1960). Thus, C. nigrivit- tatus intervenes between the Trinidad capuchin, C. albifrons trinitatis, and the nearest mainland sub- species of C. albifrons. Hershkovitz (1972) states that "the Trinidad capuchin was, almost certainly, intro- duced by man." We know little about the total extent of the distribu- tion of the red howler monkey, A. seniculus, in Trinidad and Venezuela. The extension of the popula- tion data that I obtained at my study sites becomes increasingly speculative when extrapolated to larger areas. For this reason, I will avoid estimating numbers of monkeys that may remain in other areas. I close instead with a discussion of the possibilities for con- servation of howlers and capuchins in Trinidad and Venezuela. STUDY SITES, METHODOLOGY, AND TECHNICAL COMMENTS The actual fieldwork for the demographic portions of this chapter consisted of 51.5 h of observations of howling monkeys in Bush Bush Forest, Trinidad, during the summer of 1968; 603 h of observation of howlers (out of ca. 893.5 field hours) at Hato Masaguaral in Venezuela in 1969-1970; and 58 h of observations on Alouatta during June and July of 1972 at Hato Masaguaral (out of 82.5 field hours). Addi- tional field time was spent at Camatagua Reservoir in Venezuela during the summer of 1972. Hato Masaguaral (Figures 1 and 2), a cattle ranch owned by Tomas Blohm, is situated approximately 50 km south of Calabozo in southern Guarico State. The ranch provides a sample of primate populations in a protected or unutilized area in the llanos north of the Orinoco and will form the basis for my discussion of demography. The Hato has extensive populations of howlers (A. s. arctoidea) and limited numbers of capuchins (C. nigrivittatus) (Neville, 1972). The Camatagua Reservoir, formed in 1969 near Camatagua in southeastern Aragua State, regulates the flow of the 101
102 NEVILLE CARiBBEAN SEA TRiNiDAD BRAZiL FIGURE 1 Venezuela: 1-7, national parks on the UN list (iUCN, 1967); 8-9, howler study sites. 1. Henry Plttier (Rancho Grande). 2. Guatopo. 3. Sierra Nevada de Merida. 4. El Avlla. 5. Yurubi. 6. Yacumbu. 7. Canaima. 8. Camatagua Reservoir. 9. Hato Masaguaral. Guarico River and supplies water to Caracas. Its watershed has extensive howler and limited capuchin populations. The basic approach to censusing was to record directions of dawn howls, track down the troops, and make counts. However, A. seniculus troops do not always participate in the dawn chorus (a variability also reported by Chivers, 1969, for A. palliata on Barro Colorado Island). Chorusing frequencies range from % percent (22 of 23 mornings for the WHT troop from Bush Bush) to 18 percent (4 of 22 mornings for Troop 1 of Western Forest, Hato Masaguaral). One of the possible factors influencing the variability is den- sity in a limited region. However, even some of the most densely packed troops occasionally failed to participate in the dawn howl. Walking through an area and counting animals, one may miss entire troops. Howlers may remain un- noticed in a small tree unless an animal happens to move or vocalize. Vocalizations were a fairly common response to humans in Hato Masaguaral, where most of the troops were incompletely habituated and un- hunted. Where hunting occurs, however, the animals are silent and will remain motionless unless able to flee. In any given area, I believe that an accurate census can only be obtained by repeating counts of each resident troop at least twice. If a troop is cen- sused only once, there is a high probability of error due to hidden or strayed monkeys. Figure 3 shows that the 1969-1970 counts for Middle and Eastern Forests in Hato Masaguaral continued to increase as more time was invested and I became better acquainted with the area. All but two troops were counted twice in the 1972 Hato census. For 5 of the 17 troops that were counted more than once, the first count was incomplete. Correct ascertainment of sex and age also profits by repeated counting. Howlers also are notoriously dif- ficult to maintain in zoos, hence I was not able to obtain a mental image of size, shape, and behavioral changes correlating with age classes before going into the field. The correlation of field categories to a chronological scale had to be made in retrospect and is therefore improving with continued work. The basic criteria for age assignment in this report were shape of the female genitalia, the male head and throat, and size. Animals assigned as infants were approximately 0 to 10 or 12 months of age. The juvenile stage appeared to last from ca. 1 yr of age to 2.5 yr, the criterion for the end point being a change in the female genitalia with the clitoris losing prominence relative to the labia. The size achieved by females of this stage was used to define the lower size limit for small subadult males. The subadult female stage ap- peared to last approximately 1 yr, until the female achieved essentially full size and adult configuration of the genitalia. Some individuals, however, retained an intermediate appearance even after giving birth. The category of adult male was assigned to males of apparently full size in body, throat, and beard; it may have taken 2 yr beyond the juvenile stage to achieve fully adult characteristics. Utilizing some behavioral features on occasion to make assignments is almost unavoidable (e.g., an individual making a deep, dawn howl must be an adult male, or an imperfectly seen individual crawling jerkily over the body of a large monkey must be a recent infant). In particular, discussion of variability in de- velopment both of behavior and of size and anatomical features requires a large sample of animals with known birth dates. The infant and juvenile categories were divided into three approximate sizes and the subadults into two. These categories probably have a crude relation to chronological age and may indeed approximately equally subdivide the large category. Conflicts in age assignment with the same animal were usually be- tween two of the adjacent finer categories and were not considered serious. Chalmers (1968a,b) and Alrich- Blake (1970) provide additional discussion on the problems of censusing arboreal monkeys. DEMOGRAPHIC RESULTS In the Hato Masaguaral, howlers live in small groups (Table 1, 1972 census; Table 2, 1970 final counts). In
u> -^^m.:/' \ ~-.;*â¢1â¢/;... 5^ a -o 9-5 a. S E Â°- S 2 I! S 5 So Â« S > c I Â§ U. k. ^^ o 0 ^ e -o 0 w Sg fe = *!, !f 01 * O g -g c 8.2 103
104 NEVILLE FIGURE 3 Increase In known population of howlers in Middle and Eastern forests, Hato Masaguaral, be- tween September 11, 1969, and February 25, 1970, as a function of hours worked (searching plus observation). Major jumps in the census are due to the discovery of new troops, while small changes indicate minor changes within troops or im- provement of troop counts. Q_ O O. 10 20 30 40 50 HOURS OF WORK 60 70 80 TABLE 1 Summer 1972 Census in Hato Masaguaral: Troops Identified by Letters and Equated, in Some Instances to the Numbered 1969-1970 Troops by Identification of Individuals* Male Female Unsexed Area and Troop Ad. Subad. Juv. Inf. Ad. Subad. Juv. Inf. Inf. Total Western Forest Troop A (= I) 1 2 2 4 1 1 11 Troop B ( = 3) 1 1 1 2 1 1 7 Troop C 1 2 1 4 Troop D 1 1 1 1 2 1 7 Troop E 2 2 1 2 1 1 1 10 Troop F 2 1 1 2 2 1 9 Troop G 1 1 1 2 1 I 7 Subtotal 9 4 7 5 16 3 6 4 1 55 Middle Forest Troop H 2 1 1 1 3 1 1 10 Troop 1 (=7) 2 1 2 1 : 1 9 Troop J (=8) 3 1 2 2 i 1 10 Troop K 1 1 2 1 5 Troop L 2 1 2 1 2 8 Troop M 3 1 2 1 2 i 12 Subtotal 13 4 8 5 14 1 5 3 . 1 54 Eastern Forest Troop N 1 1 2 2 1 7 Troop O 2 3 2 4 2 2 15 Troop P I 1 3 1 1 1 8 Troop Q(= 13) 1 1 1 1 3 7 Troop R(= 15) 1 1 2 2 1 7 Troop S 2 1 2 3 I 1 10 Subtotal 8 5 8 3 17 2 7 3 1 54 TOTAL 30 â¢ 13 23 13 47 6 18 10 3 163 â¢ Inf. = infant (less than I yr); Juv. = relation to 1969-1970 ranges. juvenile (ca. 1-2.5 yr); Subad. = Subadult (duration ca. 1 yr for females. 1-2 yr for males): Ad. = Adult. See Figure 4 for
THE POPULATION AND CONSERVATION OF HOWLER MONKEYS 105 TABLE 2 Terminal Troop Counts from 1970 Troops Resident in Portions of the Hato Masaguaral Sites Recensused in 1972 Male Female Ilnsexed Area and Troop Ad. Subad. Juv. Inf. Ad. Subad. Juv. Inf. Inf. Total Western Forest 1 1 2 1 1 1 6 2b(half) 1 1 1.5 1 0.5 5 3 2 1 1 2 1 7 4a 1 1 3 1 1 7 4b 2 2 3 1 8 23 1 2 1 1 5 Subtotal 8 2 5.5 0 13 2 5 2.5 0 38 Middle Forext 2b (half) 1 1.5 1 0.5 5 7 I 2 2 6 8 1 3 2 3 2 12 9 2 1 2 1 8 10 1 : 1 3 1 1 10 17 2 1 4 I8b 3 1 i - 1 1 10 Subtotal 10 6 8.5 4 16 1 5 4.5 0 55 Eastern Forest 11 3 1 2 1 2 9 12 1 1 2 4 1 1 2 12 13 1 2 1 1 2 1 1 9 14 2 1 1 2 1 1 1 9 15 1 1 1 2 1 6 16 2 1 3 1 1 8 Subtotal 10 6 3 4 15 2 5 8 0 53 TOTAL 28 14 17 8 44 5 15 15 0 146 1972, 19 troops were censused west of the major highway crossing the ranch; the average size of these troops was 8.6 Â± 2.5. In 1970 the average for 19 troops living in the same area was 7.7 Â± 2.3. Approximately 22.5 months separates these counts. Because of the presence of recognizable individuals, some troops are identified in Table 1 as descendants of particular troops in Table 2. Figure 2 shows that such troops tend to be conservative in their ranging tendency. The close correspondence of the number and locations of the other 1972 troops to 1969-1970 ranges is suggestive of other identities. It is assumed that identifiable indi- viduals, usually adult males and females, have not switched troops. Some troops indicated in Neville (1972, Figures 6 and 7) are omitted, either because their ranges fell mostly or totally outside the area recensused in 1972 or because they were judged to have been incursive in the area. Solitary animals and pairs are not indicated in the tables or the figure. To study the probability of individuals switching troops or to census nontroop monkeys would require marking of animals. Apparently the populations are steady in Eastern and Middle forests and increasing in Western Forest, my impression in 1969-1970 (Neville, 1972). A steady population level need not imply that Middle and East- ern forests are experiencing a death rate equivalent to the birth rate. I suspect that there are various be- havioral mechanisms (including the howling vocaliza- tions) that lead to emigration of groups and individuals from favorable but well-populated areas. Figure 4 presents a comparison of the age-sex structures for 1970 and 1972 in Hato Masaguaral using only the troops that appear in Tables 1 and 2. Rather than compare percentages of the population in each category, actual numbers are used so that overall population change can be observed. The problem of having nonequal age categories is apparent, but the- larger juvenile population in 1972 is striking. In Table 3 the finer divisions of juvenile and infant are employed for the 1972 census. Assuming that the small and middle juvenile categories approximate a year of growth and are therefore roughly equivalent in dura- tion to the infant stage, one notes that the second-year
106 NEVILLE AGE MALE FEMALE AD SUBAD JUV INF AD SUBAD JUV INF 30 20 I0 0 10 20 30 40 50 1972 5 4 2 I 0 5 4 3 2 30 20 10 0 10 20 30 40 50 1970 FIGURE 4 Population profiles for the 1972 and 1970 census of Tables 1 and 2. Dotted lines in infant category for 1972 indicate three unsexed infants that were arbitrarily assigned in equal portions to each sex. See text for discussion of the difficulty of correlating age categories with chronological age (present estimate indicated in years). animals number 28 as opposed to 26 first-year animals. One expects some variation from year to year, of course, but one also expects attrition. It appears that the second-year infant group may have been consider- ably more numerous than the first-year group. Table 4 compares the proportion and the ratio of females to males in each major age category for the 1972 census, the comparable portion of the 1970 cen- sus (roughly 22 months before the 1972 census), and the larger census for the 26 troops of the 1969-1970 AD 1 AD Q 1 1 Q A n o U O AU SUBAD JUV JUV INF INF study (Neville, 1972, Table I). The added value of the latter through the increase in number is partially diminished by the extended time through which the census was taken (average values taken by averaging the first and last representative counts for the troops) and the fact that it contains troops not recensused in 1972. The unusually large juvenile proportion in 1972 is again striking, as well as the general agreement in age proportions between the 1970 census and the larger 1969-1970 census of which the 1970 census is a part. Comparison of the sex ratios in the 1970 and 1969- 1970 censuses indicates that one needs a large sample size for accuracy (in estimation of a hypothetical population equilibrium ratio), the infant ratio in par- ticular being very variable. The adult sex ratios are remarkably stable, part of which is surely accidental. The subadult ratios imply that the subadult male stage lasts at least twice as long as that of subadult females. From knowledge of other monkeys (mostly ma- caques), one would expect attrition, at least in the form of out-migration, of subadult males also to be higher than that of subadult females. The longevity of howlers in the wild is not known. We are only beginning to appreciate the possibilities for some catarrhine popula- tions (rhesus and Japanese macaques and chimpan- zees) on which extended longitudinal studies with identified individuals have been made. While the population of howler monkeys in this part of Hato Masaguaral is probably growing, the persis- tence of the trend is untested. Data is almost com- pletely absent on several aspects of howler popula- tions dynamics: the fate and abundance of solitaries, the effects and frequency of group transferals, and the epidemiology of the howler population. A good demo- graphic analysis of a primate population needs a population profile with the age categories stepped in equal progressions (Heltne et al., this volume). Field data are very difficult to convert into this form when the study population lacks a sharp birth season. Many of these questions could be answered if the monkeys could be marked in some fashion that would not TABLE 3 Age Structure of the 1972 Census Using Finer Subdivisions within the Juvenile and Infant Categories Juvenile Infant Sex Adult Subadult Large Middle Small Large Middle Recent Total Male 30 13 8.5" 6.5" 8 3 9 1 79 Female 47 6 5 8 5 4 6 0 81 TOTAL 77 19 13.5 14.5 13 7 15 4 163" " One individual was described in the notes as "large/middlish." * Three infants were not sexed.
THE POPULATION AND CONSERVATION OF HOWLER MONKEYS 107 TABLE 4 Numbers, Proportion of Total, and Sex Ratio for Each Age Category in the 1972 Census, the Comparable Portion of the Census in 1970, and the Average Count for 1969-1970, Represented by the Larger Sample in Neville (1972, Table 1) Age 1972 1970 1969-1970 Category Number Percent Fem./Male Number Percent Fem./Male Number Percent Fem./Male Adult 77 47.2 1.57 72 49.3 1.57 108 49.2 1.57 Subadult 19 11.7 0.46 19 13.0 0.36 29 13.2 0.31 Juvenile 41 25.1 0.78 32 21.9 0.88 45.5 20.7 1.27 Infant 26 15.9 0.77" 23 15.8 1.88 37 16.9 1.23" TOTAL 163 99.9 1.03 146 100.0 1.18 219.5 100.0 1.18 â¢ Three infants in the total count were not sexed. * Two and one-half infants were not sexed; the one-half refers to the summarizing procedure wherein the first and last representative counts of a troop were averaged. preclude future close observer distances and would permit recensusing over several yearly intervals. CONSERVATION IN VENEZUELA Venezuela's 91,205,000 ha in 1970 contained approxi- mately 10,399,000 people (Brittanica Book of the Year, 1972), signifying that area alone still forms protection for at least some animals. The Venezuelan Division of National Parks has responsibility for more than 1,400,000 ha (i.e., 1.61 percent of Venezuela) appor- tioned among 10 national parks and 3 natural monu- ments. Six forest reserves total an additional 1,813,000 ha. The following description has been drawn princi- pally from Acosta-Solis (1968), Beebe (1949), Beebe and Crane (1947), Harrisson (1971), the UN list of National Parks (IUCN, 1967), and informational sheets (undated) from the Venezuelan Ministry of Agriculture and Husbandry, Division of National Parks. Seven of the national parks are presented in Figure 1 in addition to the locations in which I worked. Several of the northern parks have potential for primate con- servation. The most famous of the parks is Henry Pittier (formerly Rancho Grande), which consists of 90,000 ha rising from 0 m on the coast to 2,344 m in the cloud forest of the coastal Andean range north of Maracay. The laboratory buildings at 1,097 m are actively used by research scientists. The park was established in 1937 and contains howlers (personal observation) and capuchins (Beebe, 1949). The National Park of Guatopo, comprising 92,640 ha ranging from 400 to 2,200 m, was set aside in 1958 to conserve the water supply to Caracas. Conservation of water supply for farming areas and villages has been a prime reason in the formation of a number of the parks, including Henry Pittier; Sierra Nevada de Merida (160,000 ha ranging from 600 m up to the highest point in Venezuela, Pico Bolivar, at 5,007 m) (established in 1952); El Avila (66,192 ha to the north of Caracas with elevations from sea level on the coast to 2,700 m) (founded in 1959); and Yurubi in Yaracuy State (founded in 1960 to protect the water supply of San Felipe) (4,000 ha). Yacambii, 9,000 ha in the Sierra Portuguesa in Lara, was founded in 1962. Canaima, in Bolivar, is the only national park south of the Orinoco; this 1,000,000-ha park, founded in 1962, contains the famous Angel Falls. An eighth national park, the 8,500-ha Cueva de la Quebrada "El Toro" located in the Federal District (established in 1969), includes the cave "El Toro," from which flows an underground river. The cave roosts the same Sieatornis birds as the Alejandro von Humboldt Natural Monument in Monagas. The 181-ha Humboldt Monument contains the "Caves of the Guacharos," named after its famous nocturnal oil birds (Steatornis caripensis). The largest of the three natural monuments is Cerro de Maria Lionza, 40,000 ha set aside in 1960 in Yaracuy State. Aristides Rojas, 1,630 ha, dates from 1949 and conserves a rock struc- ture near San Juan de los Morros, in northern Guarico. Harrisson (1971, p. 12) notes that "wildlife refuges" can be developed in the six forest reserves, but "so far no designations are known to have been made. The rainforests of the plains north of the Orinoco (Apure, Barinas, Guarico) need special attention and consider- ation in this respect." To this, one could add the forests of Lake Maracaibo, Paria Peninsula, the mouth of the Orinoco, and the vast areas south of the Orinocoâthese harbor the great majority of the diver- sity of the Venezuelan primates (Hill, 1960; 1962; Rohl, 1959). Reserves should be set aside in these areas now. In the llanos, the relatively few concerned land- holders provide the major efforts toward active protec- tion of wildlife, e.g., Tomas Blohm on Hato Masagural. Reservoir areas and adjacent protected watershed.
108 NEVILLE FIGURE 5 Approximate lo- cations of remnant popula- tions of howler monkeys (Alouatta seniculus insulanus [Hill, 1960]) and capuchin monkeys (Cebus aIbifrons trinitatis [Hill, 1962]) in Trinidad. Locations provided by Dr. Elisha Tikasingh (per- sonal communication, 1972) from personal knowledge or discussion with others. Map redrawn from Bacon and Ffrench (1972): the three wildlife sanctuaries that re- port lists as still containing monkeys are shown num- bered: (1) Central Range Wildlife Sanctuary, (2) Trinity Hills Wildlife Sanctuary, and (3) Bush Bush Wildlife Sanctuary. Â» MAJOR CITY - MAIM ROAD Â« WILDLIFE SANCTUARY A ALOUATTA C CEBUS such as the Camatagua Reservoir, could also provide sites for conservation of primates and other wildlife. CONSERVATION IN TRINIDAD The fauna of Trinidad is closely related to that of northern Venezuela; Trinidad has probably been sepa- rated from the Paria Peninsula only since the end of the Pleistocene era (Vuilleumier, 1971). Figure 5 shows the known locations of remnant populations of howler monkeys (Alouatta seniculus insulanus) and capuchin monkeys (Cebus albifrons trinitatis) of Trinidad. The distribution is similar to that shown in Downs et aI. (1955). In general, hunting for food has been intense over the 483,000-ha island, and the expanding human population (945,210 for Trinidad and Tobago, 1970 estimate, Brittanica Book of the Year, 1972) has put considerable pressure on forests. The various wildlife sanctuaries of Trinidad and Tobago, most of which either never had or have lost their primate representa- tion, have been described by Bacon and Ffrench (1972). Donald Griffin (personal communication, 1967) re- ported that monkeys had almost been eradicated from Arima Valley, where the famous William Beebe Tropi- cal Research Station is located. Unreported, isolated populations may remain within the rugged range of hills (heights to 940 m) to the north of the highway between Port of Spain, Arima, and Sangre Grande. Of the three wildlife sanctuaries in which primates (capuchins and howlers) are reported, the Central Range Wildlife Sanctuary, occupying 2,153 ha, is a part of the Central Range Forest Reserve established in 1922. The sanctuary area came into being in 1934 with the implementation of the 1933 Ordinance No. 35 (Pyke et al., 1972). The Trinity Hills Wildlife Sanctuary occupies 6,483 ha in the Victoria Mayaro Reserve; it is part of the Trinity Hills Reserve, estab- lished in 1900. The sanctuary is now under mining lease to Texaco Trinidad Inc. and Trinidad Tesoro Oil Company (Dardaine, 1972). Oil companies may con- tribute to conservation measures through protection of unused portions of their reserves. Bush Bush Wildlife Sanctuary, 1,550 ha set aside in 1968, includes the elevated areas of Bush Bush Island and Bois Neuf Forest in the seasonally flooded Nariva Swamp, a major feature of the central eastern side of Trinidad. Bush Bush Forest has been studied since 1959, principally by the Trinidad Regional Virus Laboratory (TRVL). Protection of the area was first carried out by TRVL and then by the New York Zoological Society (NYZS), whose responsibility ended in June 1971 (Tikasingh, 1972). Since that time there has been no systematic protection, and hunters and "fishers" constitute a major threat to the wildlife (Tikasingh, 1972, personal communication). It was impossible to realistically extrapolate esti-
THE POPULATION AND CONSERVATION OF HOWLER MONKEYS 109 mates of primate populations in the Bush Bush Wildlife Sanctuary. The population density of 1.1 howlers/ha given in Neville (1972), where the difficulties of this estimate are noted, is surely too low. Only one or two groups ofCebus were encountered during the summer of 1968. The extent and location of wildlife sanctuaries in Trinidad and Tobago in general is adequate and well planned (Tikasingh, personal communication, 1972). However, it is imperative that existing laws be en- forced. There is considerable hunting pressure on the animals themselves and a persistent agricultural/ industrial threat to the forests. Trained and responsible forest officials need to be placed in each reserve. Reactivation of research in Bush Bush by an agency such as the TRVL or the NYZS. and a direct approach to enlist the active cooperation of high officials in the oil companies leasing in southern Trinidad, would proba- bly be of great help. CONCLUSIONS Our knowledge of the distributions and population parameters of primates in Venezuela and Trinidad is very incomplete. There is little data on the effective- ness of the conservation systems of these two coun- tries in relation to their primate populations. A major problem in Trinidad's Bush Bush Wildlife Sanctuary is enforcing protection. Venezuela has considerable need for the promulgation of more protected areas, as well as enforcement of existing laws. ACKNOWLEDGMENTS I wish to particularly thank Tomas Blohm and Elisha Tikasingh for their communications in respect to the conservation systems of Trinidad and Venezuela and for their assistance during my fieldwork. I am also deeply in debt to the many other individuals who have assisted me in my work. REFERENCES Acosta-Solis, M. 1968. Proteccion y conservacion de la naturaleza en Sudamerica. Pages 230-250 in E. Fittkau. J. lilies. H. Klinge. G. Schwabe. and H. Sioli, eds. Biogeography and ecology in South America, vol. I. Dr. W. Junk Publ., The Hague. Aldrich-Blake, F. P. G. 1970. Problems of social structure in forest monkeys. Pages 79-101 in J. Crook, ed. Social behaviour in birds and mammals. Academic Press, New York. Bacon, P. R., and R. P. Ffrench. eds. 1972. The wildlife sanctuaries of Trinidad and Tobago. Wildlife Conservation Committee, Minis- try of Agriculture, Lands and Fisheries, Trinidad and Tobago. 80 pp. Beebe. W. 1949. High jungle. Duell, Sloan & Pearce, New York. 379 pp. Beebe. W., and J. Crane. 1947. Ecology of Rancho Grande, a subtropical cloud forest in northern Venezuela. Zoologica (N.Y.) 32:43-60. Brittanica book of the year, 1972. Encyclopedia Brittanica, Inc., Chicago. Chalmers, N. R. 1968a. Group composition, ecology and daily activities of free living mangabeys in Uganda. Folia Primatol. 8(3-4):247-262. Chalmers. N. R. 1968b. The social behaviour of free living man- gabeys in Uganda. Folia Primatol. 8(3-4):263-281. Chivers, D. J. 1969. On the daily behaviour and spacing of howling monkey groups. Folia Primatol. 10:48-102. Dardaine, S. 1972. Trinity Hills Wildlife Sanctuary. Pages 25-30 in P. R. Bacon and R. P. Ffrench, eds. The wildlife sanctuaries of Trinidad and Tobago. Wildlife Conservation Committee, Trinidad and Tobago. Downs, E. G., T. H. G. Aitken, and C. R. Anderson. 1955. Activities on the Trinidad Regional Virus Laboratory in 1953 and 1954 with special reference to the yellow fever outbreak in Trinidad. B.W.I. Am. J. Trop. Med. Hyg. 4:837-843. Harrisson, Barbara. 1971. Conservation of nonhuman primates in 1970. S. Karger. Basel. 99 pp. Hershkovitz. P. 1949. Mammals of northern Colombia. Preliminary report no. 4: Monkeys (Primates), with taxonomic revisions of some forms. Proc. U.S. Nat. Mus. 98(3232):323-427. Hershkovitz, P. 1972. Notes on New World monkeys. Int. Zoo Yearb. 12:3-12. Hill, W. C. O. 1960. Primates: Comparative anatomy and taxonomy. IV. Cebidae. Part A. Edinburgh University Press, Edinburgh. 523 pp. Hill, W. C. O. 1962. Primates: Comparative anatomy and taxonomy. V. Cebidae, Part B. Edinburgh University Press, Edinburgh. 537 pp. IUCN (International Union for the Conservation of Nature and Natural Resources). 1967. Liste des Nations Unies des parcs nationaux et reserves analogues. IUCN Publications, New Series, No. 11. Hayez. Louvain. Belgium, 550 pp. Neville, M. K. 1972. The population structure of red howler monkeys (Alouatta seniculus) in Trinidad and Venezuela. Folia Primatol. 17:56-86. Pyke, S.. P. R. Bacon, R. P. Ffrench. and B. S. Ramdal. 1972. Central Range Wildlife Sanctuary. Pages 20-24in P. R. Bacon and R. P. Ffrench, eds. The wildlife sanctuaries of Trinidad and Tobago. Wildlife Conservation Committee, Trinidad and Tobago. Rohl, E. 1959. Fauna descriptiva de Venezuela (vertebrados), 4th ed. Neuvas Graficas, Madrid. 516 pp. Tikasingh, E. S. 1972. Bush Bush Wildlife Sanctuary. Pages 67-71 in P. R. Bacon and R. P. Ffrench, eds. The wildlife sanctuaries of Trinidad and Tobago. Wildlife Conservation Committee, Trinidad and Tobago. Vuilleumier, B. S. 1972. Pleistocene changes in the fauna and flora of South America. Science 173:771-780.