AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 84:43-58 (1991)

Demography and Social Organization of Free-Ranging catta in the , ROBERT W. SUSSMAN Department ofdnthropology, Washington University, St. Louis, Missouri 63130 KEY WORDS , Population structure, Fertility, Mortal- ity, Migration ABSTRACT In 1987, a long-term study of the demography of Lemur catta was begun in southern Madagascar. Eighty-five ringtailed lemurs were captured, marked, and released. Adult age classes were estimated using patterns of dental attrition. Including young, 155 individuals from nine groups were identified and monitored over 18 months. The study population of the reserve remained stable, with a growth rate of 0.98. Group sizes ranged from nine to 22 individuals (mean 14). Home ranges were larger (32 ha) and population densities lower (135/km2)than those for previously studied popu- lations, and there was a relationship between habitat quality (e.g., no. of large trees) and these factors. At the beginning of the study, there were more adult males than females, but the sex ratio reached 1.00 by the last census. Females first gave birth at 3 years of age, and 80% or more of the females gave birth in 2 consecutive years. Fifty-two percent of the infants died in the first year and, given preliminary findings, only 40% of those born reach adulthood. Age- specific fertility patterns were similar to those reported for anthropoid pri- mates. Forty-seven percent of the adult males migrated or were missing within a year. This included 78% of the 3-4 year olds and 38% of older age classes. No females were observed to migrate. One group split during the study. Demo- graphic patterns are discussed and related to patterns in other populations of ringtailed lemurs as well as in anthropoids.

Although a number of demographic stud- behavior and organization of primate popu- ies have been conducted on free-ranging an- lations (see, e.g., Packer, 1979; Dunbar, thro oid primates (see Richard, 1985, and 1984,1985;Altmannet al., 1988).As natural Duni ar, 1986, 1988, for recent reviews), plant communities continue to decrease, there are few demographic data availableon these data will become increasingly impor- natural populations of prosimians. Thus, we tant in our attempt to conserve remnant know little about the dynamics of these op- primate populations. ulations or life-history variables in t 1: ese In this paper, I report preliminary results species. Furthermore, studies of primate of a pro osed long-term study of the demog- opulations in which individuals are tagged raphy oF a population of free-ranging Lemur For long-term identification are still ex- catta in the Beza Mahafaly Reserve in south- tremely rare. Knowledge of life-history tac- ern Madagascar. Apart from a parallel study tics and PO ulation dynamics is critical to an being conducted on Propithecus varreauxi in underst ansing of the relationships that exist the reserve (Richard and Rakotomanga, in between animals and their environment press), no other demographic study of indi- (Caughley, 1977; Stearns, 19771, as has been viduals tagged for long-term identification demonstrated in a number of primate stud- exists for natural populations of prosimians. ies (e.g., Otis et al., 1981; Strum and West- ern, 1982; Ohsawa and Dunbar, 1984; Dun- bar, 1987; Cheney et al., 1988).Demographic patterns also play a key role in the social Received January 20,1990; accepted May 23,1990.

@ 1991 WILEY-LISS,INC. 44 R.W. SUSSMAK L. catta is one of the most studied of the from the river, the forest becomes more xero- Malagas lemurs and a population, living in phytic in character, with trees becomin 97 ha o the in southern smaller and more densely distribute % Madagascar,P has been censused intermit- (Sussman and Rakotozaf , in preparation). tently since 1972 (Budnitz and Dainis, 1975; Major tree species inchdy e Azima tetracan- Mertl-Millhollen et al., 1979; Jolly et al., tha, Cruteva excelsa, Acacia rovumae, Eu- 1982; OConnor, 1987). However, individu- phorbia tirucalli, Quiuisianthe apinae, Sal- als in this population have not been marked vadora augustifolia, and a numfl er of species or consistently identified, and there have of Grewia. Tree species endemism is about been lapses of several years between cen- 70%. One square hectare paths have been suses. Thus many basic questions have re- cut throughout this portion of the reserve, mained unanswered. For example, we need and paths are color coded and trees are to know more about fertility rates, age of marked to facilitate locating groups and females at first birth, interbirth intervals, mapping day and home ranges. and infant mortality rates. We know little Southern Madagascar is characterized by about general mortality rates and rates of a dry season and a wet season, althou h the population growth. We know that individu- amount of rainfall can vary tremen2 ously als migrate between groups, but we do not from year to year. Annual rainfall in the know rates or patterns of migration. Do all region of the reserve is about 750 mm, of males migrate, what are the ages of migrat- which 600 mm falls during the austral sum- ing individuals, do natal males migrate, do mer, November-March. The wet season is animals disperse to neighborin or distant also characterized by high ambient temper- groups, and do females migrate.3 These are atures, averaging between 34°C and 35"C, some of the uestions we are addressing in and reaching highs of 48°C. Average temper- this study. I?ntil we have answers to these atures during the driest and coolest months basic questions, such things as relationships (June-August) range between 23°C and between opulation dynamics and environ- 30°C and can fall to 3°C at night. During this ment, or Pife-time reproductive strategies of time, conditions are very dry, and most tree individuals, will remain unknown. species lose their leaves. Annual tempera- tures average 25°C. These data are from the STUDY SITE meterolo 'cal station at Betioky-Sud (1951- Research was conducted in southwestern 1980) an%l do not reflect microclimatic differ- Madagascar at the Beza Mahafaly Reserve. ences that might occur between this station This reserve was established in 1978 and and the reserve. decreed a Special Government Reserve in 1986 (Richard et al., 1987). Beza Mahafaly is METHODS the field site for a cooperative interuniver- Between June, 1987, and February, 1988, sity project coordinated by the School of Agronomy of the University of Madagascar, Washington Universit , and Yale Univer- sity. The project was Beveloped to promote conservation, education, research, and de- velopment in southern Madagascar. Beza Mahafaly is located ca 23'30's lat., 44"40'E long., about 35 km northeast of Betioky-Sud (Fig. 1). The reserve is divided (Phillips-Conroy, personal communication), into two parcels, one of 500 ha containing but smaller amounts proved to be insuffi- desert-like didierea forest and the other ap- cient. A total of 80 animals were captured proximately 80 ha of gallery forest. The re- and, including five animals caught in a pre- serve boundaries are fairly arbitrary and are vious study (Ratsirarsan, 1987), 85 animals contiguous with forests of the same type are now marked for individual identifica- throughout the region. The study was con- tion. Juveniles were relatively easy to iden- ducted at the latter site, referred to as parcel tify and were not routinely darted. Only 1. This parcel is completely enclosed by a three adults in the nine groups were not barbed-wire fence. It is dominated by Tama- captured. Groups were recensused by M. rindus indica trees and is characterized by a Sauther and J. Kaufmann in November, relatively tall canopy forest bordering the 1988. Includin infants and 'uveniles, a total Sakamena River. As one moves east to west of 155 individg uals were i d entified during DEMOGRAPHY OF LEMUR CATTA 45

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Fig. 1. Map of the location of the Beza Mahafaly Special Reserve. 46 R.W. SUSSMAN this study, including all members of nine RESULTS groups. Demograp hic structure Each animal was given a nylon collar with a numbered plastic tag. The color of the Tables 1-3 present the composition of cen- collar identified the group, the color of the sused groups at three different times over an tag identified the sex of animals within each 18 month eriod: just after the birth season group, and the shape of theta identified the in Septeder, 1987; in Janua , 1988, dur- individual. In this way the it entification of ing male migrations; and after 7t e 1988birth the individual could be made quite easily and season in November. Eight heterosexual quickly, even when the tag number was not groups and one all-male group were included visible. in the first census (Table 1). By January, While the animals were tranquilized, the 1988, three females and one male had s lit following information was collected: weight, from Yellow group, forming group Ye1 ow reproductive state, general physical condi- Prime (Table 2). This also was during Pthe tion, internal body temperature, dermatolo- period (December-May) when some males glyphs, hair samples, external arasites, fe- were attempting to change groups. By this cal samples, dental casts and a Ifescription of census, 11 males emigrated or were missing the dental condition, and body measure- from the population, and four new males had ments. Ear notches were given to many indi- migrated into it. Other males changed viduals, but natural marks made these diffi- grou s within the study population, includ- cult to use for identification. The age of adult ing tR e three males from the all-male group individuals was estimated b tooth wear. (Brown B) who joined s linter group Yellow Immature animals were age2 by their size. Prime. Five (20%) oftg e 1987 infants had The population was divided into the follow- died by this second census (Table 2). By ing age classes: infant, 1year old, 2 year old, November, 1988, dispersing males had set- young adult (34 years old), young prime, tled into new groups (although not necessar- prime adult, late prime, and old. Most L. ily the group they had originally attempted catta are born within a 5 week period each to enter), and the 1988 crop of infants was year, and age cohorts in the immature age born. Thus differences between censuses re- classes are quite distinct. Determinations of flect births, deaths, age changes, male mi- relative age classes were usually made inde- gration, and grou fission. The dynamics of pendently by two or more observers, and these changes wil fbe discussed in the follow- rarely did observers disagree. However, esti- ing sections. mates such as these can be subject to error, Table 4 summarizes key statistics reflect- and the number of years re resented by each ing the social structure of this population adult age class is impossib e to determine at during the three census periods and com- this point. P pares them with data from previous studies.

TABLE 1. 1987 census (after the birth season)' Group M F I JM JF J? Total Yellow 6 6 3 3 18 Brown B 3 3 Tan West 5 4 3 3 1 16 Green 5 3 3 3 3 17 Red 4 3 3 3 1 14 Blue 5 2 2 1 1 11 Black 2 3 3 1 1 10 Tan East 5 4 4 1 2 2 18 Brown South 4 4 4 3 2 17 Totals 39 29 25 15 11 5 124 Mean 4.5 3.6 3.1 3.9 15.13 M/F ratio = 1.34 'In this and the following tables M, male; F, female; I, infant; JM, juvenile male; JF, juvenile female; and J?,juvenile of unknown sex. DEMOGRAPHY OF LEMUR CATTA 47

TABLE 2. 1988 census (during male migrations) Group M F I JM JF J? Total 1 2 Yellow 3 3 2 2 10 -2 Yellow Prime 1 t 3 3 1 1 9 Tan West 3 4 3 2 1 13 -2 Green 3+2 3 2 3 3 16 -2 +1 Red 2+2 3 3 1 1 7 -3 Blue 2 2 1 1 1 7 -3 Black 2 3 2 1 1 9 Tan East 5+ 1 4 3 1 2 2 18 +I Brown South 4 + 2 4 3 3 2 18 +2 Totals 35 29 20 12 11 5 112 (-11) (+4) Mean 3.9 3.2 2.2 3.1 12.4 M/F ratio = 1.21 'This column includes the number of males emigrating out of a group. %dicates the number of males entering a group from outside of the reserve population. The + in the column for (M) indicates the total number of males attemptingto immigrate into a group;thus for Green group, two males left the group and two males entered the group, one from outside of the reserve.

TABLE 3. 1988 census (after the birth season)' Group M F I JM JF J? Total Yellow 3 3 3 2 2 13 Yellow Prime 4 3 2 9 Tan West 4 4 1 2 2 13 Green 4 5 5 2 1 17 Red 3 4 3 2 12 Blue 4 2 1 2 1 10 Black 2 4 4 2 12 Tan East 4 4' 4' 1 2 15' Brown South 7 6 5 2 2 22 Totals 35 35 28 Mean 3.9 3.9 3.1 M/F ratio = 1.00 'A Tan East female and her infant died shortly after the 1988 birth season, leaving 13 animals in this group at the end of the study

TABLE 4. Group structure of censused Lemur catta populations Beza Beza Beza Previous Nov. 87 Feb. 88 Nov. 88 studies' No. of groups 8 9 9 Avg. group size 15.1 12.4 13.7 13.4 (n = 57) Mean No. adult M 4.5 3.9 3.9 5.2 (n = 10) Mean No. adult F 3.6 3.2 3.9 6.0 (n = 10) Mean No. infants 3.1 2.2 3.1 2.9 (n = 10) Mean No. juveniles 3.9 3.1 2.8 3.3 (n = 10) Adult M/F ratio 1.34 1.21 1.00 0.87 (n = 10) Range M/F group 0.67-2.5 0.67-1.67 0.5-2.0 0.5-1.5 (n = 10) Immature/all adults 0.82 0.75 0.76 0.55 (n = 10) Immature/adult F 1.93 1.65 1.51 1.03 (n = 10) Total population 124 112 123 Total Beza Mahafaly population just before 1988 birth season = 95 'Jolly (1966, 1972); Sussman (1974); Budnitz and Dainis (1975); Mertl-Milhollenet al. (1979);Jolly et al. (1982). 48 R.W. SUSSW Average group size was about 14 animals in portion of the reserve. During the first 8 the nine groups and individual months of the study, the home ranges of ranged from nine to 22 animals. Ppshis is groups bordering the Sakamena River aver- similar to results from previous censuses in aged 17 ha, whereas those found mainly in which groups have averaged about 13 and the dryer section of the forest averaged about ranged from five to 27 individuals. Adult sex 32 ha (Fig. 2). Over the total 18 months, two ratios of ringtail grou s normally are close to of the river groups enlarged the size of their 1.00. The Beza Ma R afaly population, al- ran es (to 31 and 26 ha, respectively) espe- though it began with more males than fe- cia1 y to feed on the fruit of Satvadora augus- males, reached an equal ratio by the last tifoliak trees during October and November, census as the result of female maturations which are located only in the dryer portion of and adult male migration (see below). The Parcel 1 (Fig. 3). A third river group (Red) total population size after the two birth sea- extended its range to the south of the fenced sons remained essentially stable, 124 ani- portion of the reserve. Including this sea- mals in November, 1987, and 123 in Novem- sonal expansion, the average home range of ber, 1988 (growth rate = 0.98). However, five grou s (whose ranges were known over because of infant mortality and male emigra- 18 mont1: s) was 32 ha (range 26-35 ha). tion, the population dropped to 112 animals These ranges are much larger than those by January, 1988, and reached a low of 95 previously re orted for L. catta living in animals just before the 1988 infants were undisturbed K abitats (6-23 ha). As was born. found in the Berenty population, the home Six of the nine groups had home ranges ranges of oups at Beza Mahafaly had located almost entirely within the fenced highly overP- apping boundaries. In the study

Fig. 2. Map of the home ranges of groups within the reserve. DEMOGRAPHY OF LEMUR CATTA 49

Ff. 3.. Map of rimar and seasonall expanded home ranges of oups Black and Blue. and the istribution ofiarge #amrmdus itdua and Saluadom augusti&~ trees along grid paths.

TABLE 5. Home range size and densities Disturbed forest Beza Mahafaly Previous studies1 O'Conner (1987) Avg. home range size (ha) 25 (n = 6) 10.34 (n = 5) 23.4 (n = 2) 32 w/seasonal expansion (n = 5) Range (ha) 16-35 5.7-23.1 12.2-34.6 Population densit (per km2) 90-135 147-350 17.4 Biomass2 (kg/krnq 200 - 48.7 - 'Jolly (1966), Sussman (1974), Budnitz and Dainis (1975). 2BiomassatBezaMahafalyis basedonaverageadultweightof2,211 g(n=65):maleavg. =2,213g(n=41),femaleavg.=2,207g(n=24), 52 avg. = 1,673 g (n = 12), J1 avg. = 1,175 g (n = 2). Biomass reported by OConner was based on captive adult weights from Tattersall (1982) (avg. = 2,760, n = 11). population, groups had few or no areas of reserve). Four months after the birth season, exclusive use. density was about 115/km2and 'ust before Table 5 summarizes data on home ran e the birth season about 90/km2.T h ese densi- sizes, population density, and biomass. T e ties are much lower than those reported for population density was estimated to be ap-a other ringtailed lemur populations in undis- roximately 125-135/km2 'ust after the turbed areas (147-350/km2). However, i&irthseasons (using the eigh t groups with OConnor (1987) found an extremely low home ranges within the 80 ha fenced density (17/km2) in a disturbed and previ- 50 R.W. SUSSMAN ously hunted forest. The biomass of ring- cycle for u to 3 months (Evans and Goy, tailed lemurs at Beza Mahafaly was approx- 1968). Birtis generally are restricted to a imately 200 kg/km2. 2-3 week period. During the study, in both The density of animals and of groups was birth seasons, most infants were born be- higher in the portion of the forest containing tween September 18 and October 25, with lush gallery forest bordering the Sakamena one or two females giving birth ap roxi- River (Fig. a), reaching about 175/km2.This mately 3-4 weeks later each year. $!here gallery forest differed in tree species compo- were no twins in either season, although sition and in density from the transitional twins are common at Berenty and in captiv- vegetation to the west of the river, contain- ity (e.g., at the Duke Primate Facility, 27% of ing half as many individual trees but 2.5 148 births have been twins or, in one case, times as many large canopy trees over 25 cm tri lets; A. Katz, personal communication). diameter at breast height (dbh) (230 vs. 90/ 1987,25 of the 29 adult females at Beza ha) (Sussman and Rakotozafy, in prepara- Mahafaly bore infants, and, in 1988,28 of the tion). A relationship between habitat uality 35 females did so, yielding birth rates of 0.86 and home range size was also reporte3 for L. and 0.80, respectively. Thus, as was reported catta at Berenty. One group living in the lush previously (Budnitz and Dainis, 1975;Mertl- gallery portion of this forest had a home Millhollen et al., 19791, ringtails have a very range of 8.1ha, and a second group of similar high birth rate, and the majority of females size living in a dryer ortion of the forest had ve birth every year. Females at Beza Ma- a home range of 23.1 K a (Budnitz and Dainis, i? afaly did not give birth until their third 1975; Budnitz, 1978), and the density of year, although females in captivity com- ringtails is over three times higher for ve birth at 2 years of age (Taylor, groups near the river (OConnor, 1987). 1986; atz, ersonal communication). The sizes of groups in the two microhabi- monlyaA e-speciffc fertility rates are given in tats at Beza Mahafaly did not differ signifi- Tabfe 6. As can be seen for 1987 and 1988 cantly, whereas home range sizes in the two combined, birth rates for prime adult fe- habitats were significantly different males are very close to 1.00. Young adult (P < .001, Student’s t test). Given the distri- females (34 years of age) have a slightly bution of trees at Beza Mahafaly, all else lower fertility rate than prime females over being e ual, groups living in the dry portion the 2 year eriod. Those females classified as of the Borest would need home ranges of old showe considerably lower fertility than approximately 37 ha to have the same num- other classes,B with none of the four females ber of large trees (about 3,450) as groups in this category ‘ving birth in 1988. In fact, living near the river with home ranges of 15 two of these olfindividuals were the only ha. This does not differ greatly from the females not giving birth in either year. actual home range sizes of the groups-- in Although annual birth rates are very high, question. infant mortality is also relatively high (Table Since the boundaries of all the groups do 7). Between the birth seasons of 1987 and not fall comdetelv in one microhabitat or 1988,52% (13 of 25) of the infants died. Five another, a bdter comparison of habitat qual- (20%) of these had disappeared within the it might be made by estimatin first month. Five of the 28 (18%)infants born oH trees in each hectare in 1988 also were missing within 1month. In given group. Two of the this small sample, young prime and prime Green) were studied intensively for 13 females had above average rates of infant months (Sauther, in press) and their ranges survival and none of the infants born to old were the best known. Black had a home females survived the first year. High infant range of 20 ha (excluding seasonal expan- mortality also has been reported at Berenty. sion), containing an estimated 4,460 large trees, and Green had a range of 34 ha, with Mortality an estimated 4,600 large trees. As always, causes of mortality are difficult to pinpoint. Probable causes of death among Birth rate and infant mortality L. catta are seasonal malnutrition, arasite L. catta females are sexual1 receptive for infestations, disease, accidents, anlgreda- 1-2 days (Van Horn and ResE 0, 1977), and tion (especiallyby large birds of pre , omes- most females normally mate within a 2-3 tic dogs, and, in some regions, iumans). week period each ear. In ca tivity, a female Table 8 gives the number of individuals in not impregnated Buring the r)irst estrus, may each age-sex class for the total population DEMOGRAPHY OF LEMUR CATTA 51

TABLE 6. Age specific fertility rates 1987 1988 No. adult Fertility No. adult Fertility 1987 + 1988 females Births rate females Births rate fertility rate 3-4 years 4 4 1.00 8 6 0.75 0.83 Young prime 3 3 1.00 4 3 0.75 0.86 Prime 13 12 0.92 15 15 1.00 0.96 Late prime 3 3 1.00 3 3 1.oo 1.OO Old 4 2 0.50 4 0 0.00 0.25 ?? 2 1 0.50 1 1 1.00 0.67 Totals 29 25 0.86 35 28 0.80 0.83

TABLE 7. Annual infant survival and mortality rates per age class of mother (1987-1988) No. of females Births Survivors Survival rate Mortality rate 3-4 years 4 4 2 0.50 0.50 Young prime 3 3 2 0.67 0.33 Prime 13 12 7 0.58 0.42 Late prime 3 3 1 0.33 0.67 Old 4 2 0 0.00 1.00 ?? 2 1 0 0.00 1.00 Totals 29 25 12 0.48 0.52

TABLE 8. 1987-1988 age classes 1987 age classes 1988 age classes F M ? 1987 total F M ? 1988 total Infants 7 5 13 25 28 28 Juvenile (1-2 years old) 13 15 3 31 10 13 2 25 Young adult 4 9 13 8 7 15 Young prime 3 3 6 4 4 8 Prime 13 15 28 15 15 30 Late prime 3 6 9 3 4 7 Old 4 6 10 4 4 8 ?? 2 2 1 1 2 Total 49 59 16 124 45 48 30 123

after the birth season in 1987 and 1988. In comparing data presented in Table 8 Figure 4 represents an age profile by sex of and in Figure 4,there may be a differential the population during the same two periods. mortality rate between males and females at Except for the first 3 years, age-specificmor- 2-3 years of age, with death more common tality rates and survivorship schedules can- among females of this age class. If this is so, not be determined from these data at present sex ratios even out in the adult age classes, because the actual number of years per age and perhaps mortality is slightly higher class is unknown. However, these data will among young adult males. However, an become available as the younger cohorts conclusions at this point about adult mortaT - grow up and are recaptured over the years. ity patterns must remain highly speculative The longevity record in captivity for ringtails because of the possibility of year to year is about 23 years, but adults rarely live past variations in mortality due to fluctuations in 20 years in captivity (M. Jones personal environmental conditions and because of the communication). high rate of male migration. Sex ratios at 52 R.W. SUSSMAN Age Structure Subdivided by Sex birth are almost equal, as is the case in captivity (for example, there have been 57 Age 1987 Sex ratio females and 63 males born at the Duke Class per 20 class University Primate Center over the past several years; Katz personal communica- P tion). However, sex ratios at birth also ma Y P. vary great1 from ear to year, and imbaP - YA ances may ZPe recti ied by male dispersal. J 1-2 1.15 A life table for three age classes is shown in I Table 9. In this table emigrants are treated 1284 048 12 the same as deaths, so survivorshi is most likely underestimated for the a f;ult age Overall Sex Ratio (malesMernales) =1.20 class. Given these preliminary data, a prox- imately 40% of the infants born woul CQreach Age Sex ratio adulthood. Class 1988 XQ per class Between November, 1987, and November, 1988, one adult male and one adult female were found dead. A second female was miss- YP ing and presumed dead, since female migra- YA tion has not been observed. This 'ves a J-2 mortality rate of 0.07 for females anB a min- imum rate of 0.03 for males. However, 11 males were missing, and one was found dead 128404812 after the first year, and the maximum adult male mortality might be 0.31. Since male Overall Sex Ratio (males/females) =1.07 migration is the norm in ringtails, it seems Fig. 4. Age structure divided by sex of the population more accurate to assume that adult male and ofL. cattu in Beza Mahafaly in 1987 and 1988. female mortality are somewhat similar, about 7-8% er year, and that a total of three or four aduf t males may have died. Mertl- Millhollen et al. (1979) ity of 0.08 at Berenty. If true, the remaining eight grated from the study population.

TABLE 9. Life table for three age classes (1987-19881 No. entering No. dying Proportion leaving Proportion surviving age class or emigrating age class from birth to age Infant 25 13 0.52 0.48 Juvenile 31 7 0.23 0.37 Adult 68 14 0.21 0.29

TABLE 10. Rates of migrating or missing males and females No. missing Total no. Maximum migration Maximum migration or migrating in class rate per year Young adult 7 9 0.78 1.28 Young prime 1 4 0.25 4.00 Prime 5 16 0.31 3.20 Late prime 4 7 0.57 1.75 Old 2 6 0.33 3.00 ?? 1 1 Totals 20 43 0.47 2.15 Females 1 29 0.03 29.00 DEMOGRAPHY OF LEMUR CATTA 53 Migration and group fission males continue to migrate throughout their lives. A total of 20 of the known adult males The common pattern of male migrations either attempted to migrate or were missing observed by Jones at Berenty was a pair of by the November, 1988, census (Table 10).As males migrating into an adjacent group. At was stated above, the fate of 11 of these Beza Mahafaly, ten transfers were followed, animals remains unknown, and one died. and no simple pattern emerged. All males One young adult male attempted to migrate initially left their group or entered a new but was unsuccessful and returned to his group with one or two partners. However, original group. Seven males successfully mi- artners did not always remain to ether. grated into new groups (four of these immi- Fhree pairs attempted to move into afjacent grated into the reserve population). Thus groups, but only one individual among them 47% (20 of 42) of the adult males attem ted was successful in transferring on first at- to mi ate or were missing after the first tempt (i.e., was still in the new group by the year. Fhe maximum number of successful next birth season). This was a prime male migrations was 42% (11 + 71, and the mini- who transferred from Blue to Red. His part- mum rate of migration was 16%.If the adult ner, a natal male, was unsuccessful and male mortality rate was 0.08 as predicted returned to his natal group (Blue). Both above, the rate of migration would be about males of the second pair were unsuccessful 40%, with males migrating on average every in their initial attempt to transfer (into 2.5 years. Jones (1983) reported a maximum Green). One of these males (a natal male) migration rate of 30% for males in the Ber- subsequently disappeared, whereas the sec- ent PO ulation in one year. In the Beza ond (a late prime adult, No. 60) transferred Ma KPafa y population, one prime adult male successfully into a third oup (Blue). An- first captured on September 19, 1985, (Rat- other late prime male left %s group (Green) sirarson, 1987)was still in the same group in and attempted, with No. 60, to transfer into November, 1988,3.3 years later. Blue. He remained with this group for 3 Only one of the adult females was missing months and then subsequently disa peared. in the last census. A second female died after Thus none of these males successfurp y trans- the birth season in November, 1988. I as- ferred with a partner. sume that the former female also died. If she Two partnerships were successful in did migrate, the migration rate would be transfers, but the original group member- 0.03, and the rate of female migration would shi of these individuals was unknown. Two be once every 29 years. maesf successfully joined a roup (Brown Seventy-eight percent of the young adult South) from outside the stuf PO ulation, males (34years old) in the population mi- and the three males of the aH-ma?e group grated or were missing, compared with 38% (Brown B) joined the splinter group Yellow of the adult males of older age classes. Young Prime. Whether this all-male group was adults and late prime adults mi rated (or composed of individuals who left the same were missing) more than average. fi rime and grou or joined together after being unsuc- young prime males were the least likely to cess ul in transferring the previous year is migrate but also had the most known suc- unknown.P cesses in migrating into new groups (Table One further change occurred within the 11).Thus, as in many primate species, young population durin the tenure of the study. males leave their natal group and older adult Group Yellow spit,f with three of the six

TABLE 11. Fate of males missing or migrating Not Not Rate of No. in Fate Successful successful successful known class unknown transfer (return) (unknown) Dead success Young adult 7 2 2 1 1 1 0.29 Young prime 1 1 1.00 Prime 5 3 2 0.40 Late prime 4 2 1 1 0.25 Old 2 2 0.00 ?? 1 1 1 .oo Totals 20 9 7 1 2 1 0.35 54 R.W. SUSSMAN adult females and one of the six adult males we find these populations more stable than forming group Yellow Prime. As stated other habitats in which primates have been above, soon after this group fission occurred, studied? Do diurnal prosimians have a the three adult males of all-male greater ability to maintain opulation stabil- Brown B attempted to join group ity than do anthro oids? Ipf the prosimians Prime. By the end of the mating season, are in a fine-tuneIf equilibrium with their these three males were fully inte ated into environment, will slight perturbations cause the new group. After the group spY it, the two major stress to these o ulations, as is indi- splinter groups still occupied the same home cated by the extremePP y ow population den- range but were never seen together. sit in the disturbed forest studied by O’zonnor (1987)? Since the arrival of hu- DISCUSSION mans in Madagascar 1500-2000 years ago, This study is the be ‘nning of a long-term at least 14 species of the lemur have become research project in wK: ich we ho e to con- extinct. As yet, we do not know if the ring- tinue to monitor the population of E. catta at tailed lemur or sifaka populations at Beza Beza Mahafal over many years. However, Mahafaly are stable over long eriods. the results o Pthe present report must be A number of investigators !l ave found a considered prelimina , since only 18 relationship between opulation size and re- months are represente7 During this short source abundance. Por example, Dunbar period of time, the population size remained (1987) found a si ificant correlation, in stable, with a growth rate of 0.98. However, black-and-white coY obus monkeys, between this was indeed a dynamic equilibrium. group size and the total number of large Changes occurrin during the ear included trees. He speculates that the total number of births, infant an% adult deatK s, male dis- large trees provides a better estimate of persal, and grou fission. Adult sex ratios gross volume of food than does a simple also changed wit in the population over the measure of preferred food trees. study period. R Terborgh (1986) has recently suggested that for any species there is an o timum Population structure group size, given the s atiotempora disper- Few primate populations studied to date sion of its ma or foo $resources, andP that have been found to be numerically stable group size is tJ, us relatively fixed within a (Dunbar, 1988). Many populations are de- species. Indeed, among L. catta in this study clining because of natural climatic changes and at Berenty, group size did not differ or human influences on their environment significantly between habitats, but home (e.g., Struhsaker, 1973; Mittermeier and range was closely correlated with the num- Cheney, 1986). Other populations are in- ber of large trees within the range. Relation- creasing rapidly, usual1 due to provisioning ships between habitat quality and home or other human induce changes (e.g., Itani, range size have been established among a 1975; Dunbar, 1980;B Rasmussen, 1981; number ofbirds (e.g., Stenger Weeden, 1965; Sussman and Tattersall, 1986). If left to Holmes, 1970) and primates (e.g., Struh- their own devices, many natural rimate saker, 1967; Takasaki, 1981). populations would probably exhibit a? ternat- ing periods of growth and decline (see, e.g., Fertility and infant mortality Southwick and Siddiqi, 1977; Froelich et al., Ringtailed lemurs have a very high poten- 1981; Winkler et al., 1984; Fishkind and tial reproductive rate. Females begin to pro- Sussman, 1987). duce offspring by the second or third year Of course, the fact that the size of the (third year at Beza Mahafaly), and most ringtailed population at Beza Mahafaly was females give birth every year thereafter. At stable over a short period of time means very Beza, the mean interbirth interval is 1.2 little. However, it is interesting to note that years, and age appears to be the ma or factor both prosimian populations censused at affecting fertilit . Althou h sociat factors, Berenty a ear to be demographically sta- such as a fema e’s rank ?e.g., Sade et al., ble. The siPR a a (Pro ithecus uerreauxi) opu- 1976; GouzoulesP et al., 1982; Wasser and lation has changedtttle over 20 years (% ich- Barash, 1983; Dunbar, 1984) or number of ard, 1985),and the ringtailed population has females in a group (Dunbar and Sharman, remained remarkably stable for at least 15 1983;van Schaik, 19831,have been related to years (Jolly et al., 1982; OConnor, 1987).Are fertilit in some primate populations, ring- the riverine and xerophytic forests in which tailed Pemales at Beza are generally success- DEMOGRAPHY OF LEMUR CATTA 55 ful in breeding each year. However, the fact ma'or factors influencing adult mortality, that no twins were born at Beza Mahafaly alt ough the little evidence that exists fits and that females first give birth at age 3 someA of the patterns described above. The years may indicate that there is some degree one adult female found dead died, along with of environmental stress in this population her infant, within a month of the infznt's (see, e.g., Altmann et al., 1988). birth. The dead adult male was first missing Age-s ecific fertility rates among the Beza from his group in January, 1988, and pre- Mahafa Py ringtailed lemurs are similar to sumably was attempting to mi rate. He was those of primates for which there are data found on Ma 9,1988, recently %eceased, and available (see Dunbar, 1986) and for most there is evi ence that he was the victim of mammals and birds (Caughley, 1966, 1977; predation byB a fossa (Cryptoprocta ferox) or Clutton-Brock, 1988). Fertility is low amon feral cat (Sauther, 1989). Furthermore, young adult females and increases to a pea there is evidence that males in the process of during physical prime, then declines at olda migrating might be under nutritional stress. age. The three males of all-male group Brown B Infant mortality rates are relatively high (the only males not members of a heterosex- both in the Berenty L. catta PO ulation and ual group at the beginning of the 1988 eriod in that at Beza Mahafaly, witR 52% of the of male migration) weighed significantP y less infants dying in the first year in the latter than all other adult males (P < .001, Stu- site. At present we have too few data to dent's t test). The average weight of all adult discern any patterns in infant mortality. males was 2,213 g (N = 41, range 1,700- Around 20% of the infants born in 1987 and 2,7751, whereas the bachelor males wei hed 1988 died within the first month. Infants 1,700, 1,825 (the only adult males weiga ing also should be especially vulnerable to pre- less than 1,900 g), and 1,950 g. These three dation and other environmental stresses at males were of three different adult age 2.5-3 months of age when they begin to move classes and all other adult males weighing independently and are being weaned, and less than 2,000 g (N = 3) were just reaching perhaps during the peak of the dry season maturity. Loss of weight in transferring when they are 10-11 months old. males has also been reported in toque macaques (Dittus, 1977). Patterns of adult mortality A number of investigators have discovered Migration and group fission relationships between adult mortality and In the majority of mammalian species in- environmental or social factors (Ohsawa and vestigated, and in most primates, males Dunbar, 1984; Teleki et al., 1976; Goodall, have a higher probability of leaving their 19861, seasonal or periodic food shortages natal group and of subsequent dis ersal (Dittus, 1977; Otis et al., 1981; Milton, 1982; than do females (Greenwood, 1980; 5usey Hamilton, 19851, and predation (van Shaik and Packer, 1986; Shields, 1987). L. catta and Hoof, 1983; Terborgh, 1986). Further- shares this pattern of male-biased dispersal. more, many factors that cause mortality may Eight of the nine censused groups were af- have differential influences on individuals of fected by migration. In the ringtailed lemur, different age, sex, or dominance status. For males leave of their own accord and are example, migrating males are assumed to be subject to agonistic attack mainly, but not more susceptible to predation, nutritional solely, by the males of the group into which stress, and agonistic attack (Dittus, 1977; they are attempting to immigrate (Budnitz Otis et al., 1981). Among females, reproduc- and Dainis, 1975; Jones, 1983; Sauther, in tion and infant care are often stressful and press). At Berenty, male migrations were mortality rates may be higher among indi- observed around the birth season, whereas, viduals who are caring for young infants at Beza, transfers occurred between Decem- (Jolly, 1984; Sauther and Nash, 1987; Alt- ber 26 (around the time infants were becom- mann et al., 1988; Richard and Rakoto- ing independent) and the end of the mating manga, in press). season, May 31. Thus knowledge of the patterns of mortal- Althou h a number of investigators have ity, such as age and sex of dying individuals discusse B the possible benefits of transfer- and time of year of death, can often help us ring with group mates (see Pusey and determine some of the possible causes. Packer, 1986), in L. catta at Beza benefits Among the ringtails at Beza Mahafaly, there did not seem to accrue to both partners are not enough data to speculate on the equally. Kin selection has often been invoked 56 R.W. SUSSMAN as the reason for males to transfer together bly of unrelated natal males (Taylor and (Meikle and Vessey, 1981; van Noordwijk Sussman, 1985; Sauther, in press). Since and van Schaik, 1985) and for males to trans- central males appear to hold a favored posi- fer year after ear into the same grou tion within groups, males may transfer into (Colvin, 1983; Aeney and Seyfarth, 1983f: groups in which attaining this status seems However, since none of the partnershi s at more ossible. Beza Mahafaly were of similar-aged incp ivid- At tR e population level, the type of “trickle uals, it is unlike1 that these animals were migration” (Dunbar, 1988) that occurs closely related. Purthermore, since inter- amon L. catta appears to be important in group transfers were so frequent and com- smoota ing out minor inequalities in sex ra- plex, it seems unlikely that regular inter- tios or in numbers of animals within groups group exchanges occur, although this as well as in randomizing gene flow. How- remains to be seen. ever, group fission may be more important At Berenty, most males transferred into than male transfer in adjusting population grou s with fewer males than the groups size over a larger area. If population growth they Rad left. No sim le pattern such as this occurs within one area, emi ration of a splin- emer ed at Beza Ma E afaly, with one excep- ter group, often to a less CFesirable habitat, tion. $he two grou s with the most skewed may be a means of maintaining suitable sex ratio (Yellow 8rime and Blue) had the PO ulation densities. most individuals either immigrate or emi- 8ne roup of ringtails did split at Beza grate, and the direction of migration helped Mahafafy. By the end of the study (almost a correct the imbalance. Furthermore, the year after the initial fission), the two splinter number of males emigrating from the census groups still occupied the same home range, population (11)was greater than that joining although one group seemed to be s ending it (four), and this was a major factor in more time to the west of the reserve.kunbar equalizing the sex ratio between the 1987 (1984, 1988) has speculated that groups of and 1988 birth season. Males at Berent gelada baboons undergo fission because of transferred into adjacent groups (althougz social friction related to intrasexual compe- five of 17 were unaccounted for). The Ber- tition. This “results in intolerable levels of enty reserve is quite isolated from any other harassment (and hence re roductive sup- forest area. At Beza Mahafaly, most sus- pression through stress) !or low-ranking pected transfer males that disappeared from females.” (Dunbar, 1988: 84). It is interest- the study area were not seen in nearby in to note that the ringtailed group that oups and migrating, collared males have spfit contained more adult females than any feen spotted in separate forests 2-3 km from other group and yet had the lowest rate of the reserve. fertility. The evolutionary or adaptive significance of migration has been discussed by a number CONCLUSIONS of authors, as have the potential proximate This study must be considered prelimi- causes (see Pusey and Packer, 1986; Shields, nary, since it covers less than the amount of 1987; Dunbar, 1988; for reviews). In the time it takes for an infant L. catta to reach ringtailed lemur, sexual com etition and maturity. Our goal is to continue to monitor mate choice may be the driving orce for male this population in the future and to expand transfer. Migrations begin wellP before and the study to include some groups in unpro- culminate after the mating season. Resident tected areas outside of the Beza Mahafal males attempt to kee transferring males Reserve. Only with long-term research wi P1 out of the group, an female choice is a we be able to determine how the environ- prere uisite to matin Bsuccess. Female rin - ment influences population d amics and tailedP emurs either a low males to approac!l how demographic variables a ect and are them sexually or activelyK present to a male. affected by social or anization.iY L. catta is Unacceptable males are rebuffed. In cases listed in the IUCN fied Data book as not observed, resident central group males are threatened, yet it appears that this species allowed first access to receptive females. may be very sensitive to habitat quality and Females will also mate with peripheral change. Although high population densities males, with recently transferring males, and occur in gallery forests, ringtailed lemurs with males from adjacent, neighboring are found in much lower densities in dryer groups (Sauther, in press). Females reject vegetation. Recent satellite hotographs re- advances of closely related males and possi- veal that there are fewer t Kan 1,000 ha of DEMOGRAPHY OF LEMUR CATTA 57

emigration. In RAHinde (ed):Primate Social Relation- ships. Oxford: Blackwell, pp. 160-171. Dittus WPJ (1977) The social regulation of population density and age-sex distribution in the toque molikey. Behaviour 63:281-322. respond well to human disturbance, and Dunbar RIM (1980) Demogra hic and life history vari- knowledge of the population structure and ables of a population of gelafa baboons (Theropithecus dynamics of this species is a prerequisite to gelada). J. Anim. Ecol. 49~485-506. Dunbar RIM (1984) Re roductive Decisions: An Eco- its conservation. nomic Analysis of GeLda Baboon Social Strategies. Princeton, NJ: Princeton University. ACKNOWLEDGMENTS Dunbar RIM (1985) Population consequences of social I thank the followin people for their assis- structure. InRM Sibly and RH Smith (eds): Behavioral Ecology: Ecological Consequences of Adaptive Behav- tance in the field: G. Breen, J. Kaufmann, A. ior. Oxford: Blackwell. Lake, Manjagasy, A. Rakotozafy, K. Reilly, Dunbar RIM (1986) Demography and reproduction. In and M. Sauther. All the lemurs were darted BB Smuts, DL Cheney, RM Seyfarth, RW Wrangham without a single accident by the head guard and TT Struhsaker (eds): Primate Societies. Chicago: of the reserve, Behaligno. I am especially University of Chicago, pp. 240-249. Dunbar RIM (1987) Habitat quality, population dynam- grateful for his assistance and expertise. The ics, and group composition in colobus monkeys project would not have been possible without (Colobus guereza). Int. J. Primatol. 8:299-329. the generous aid of the Ministry of Hi her Dunbar RIM (1988)Primate Social Systems. Ithaca, Ny: Education and the School of Agronomy o! the Comstock. University of Madagascar, especially B. Ra- Dunbar RIM, and Sharman M (1983) Female competi- tion for access to males affects birth rate in baboons. kotosamimanana, B. Andriamihaja, B. and Behav. Ecol. Sociobiol. 13:157-159. V. Randrianasolo, J. 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