PRIMATES, 43(3): 23%248, July 2002 237

Home Range and Ranging Pattern in the Slender Loris (Loris tardigradus lydekkerianus)

SINDHU RADHAKRISHNA Universi O, of Mysore and

National Institute of Advanced Studies, Bangalore, India

and MEWA SINGH Umversi O, of Mysore, India

ABSTRACT. The home range and ranging pattern of the slender loris (Loris tardigradus lydekkerianus) was studied for 21 months in a scrub jungle in Dindigul, Tamil Nadu, south India. Sixteen individuals were observed for a total of 2261 hours. Home ranges were measured for eight adult individuals and eight juvenile and subadult individuals. Males had significantly larger home ranges than the females, and home range size increased post-weaning. The ranging patterns involved minimal female intrasexual overlap, large male intrasexual overlap and large intersexual range overlap.

Key Words: Slender loris; Home range; Ranging pattern; Home range overlap; Social organization.

INTRODUCTION

The slender loris (Loris tardigradus, Prosimii:Lorisidae) is a nocturnal prosimian that inhab- its the dry, wet, swampy coastal and montane forests of India and Sri Lanka (RoONWAL & MOHNOT, 1977). Six subspecies - two in south India and four in Sri Lanka - are presently rec- ognized, based on geographical locations and differences in pelage and body weight (ScHULZE & MEIER, 1995). The species has been classified 'Vulnerable' by the IUCN Red Data List (IUCN, 2000); yet, for decades, as with many nocturnal prosimians, little field data was avail- able on it.

The first field study on the slender loris was a 16-day population survey conducted in Sri Lanka by PETrER and HLADIK in 1970. They concluded that the slender Ioris was nocturnal, pre- dominantly insectivorous, and depended on the undergrowth for protection. Population densities were variable, with a maximal value of an animal per hectare, and an inter-individual spacing of about 100 m. Population surveys on the slender loris in southern India are reported by SARKAR et al. (1981) and SINCH et al. (1999, 2000). SINGH et al. (1999) observe that they had sighted four individuals within 50 m of each other in one of the areas they had surveyed.

Three studies report home range sizes for the slender Ioris; the figures were based on obser- vations of the two subspecies found in south India and differ between the studies. The two sub- species were the malabaricus and the lydekkerianus found in the wet forests of the Western Ghat mountain ranges and the dry scrub forests of the Eastern Ghat mountain ranges respec- tively. JOHNSON (1984) calculated the home range of a male slender loris of the subspecies mal- abaricus to be 0.9 ha. In a radiotelemetric study on the same subspecies, however, KAR GUPTA & NASl~ (2001) observed much larger home ranges, varying from 2.5 ha to 34 ha. NEKAmS' (2000) study on the lydekkerianus subspecies of the slender loris reports an average adult male home range size of 3.6 ha, juvenile male home range size of 1.17 ha, and adult female home range size of 1.59 ha.

238 S. RADHAKRISHNA & M. SINGH

A long-term study of the behavioural ecology of one of the populations of the lydekkerianus subspecies of the slender loris, discovered by SINGH et al. (1999), was initiated in 1997. Data from this study on the home range and ranging patterns of 16 slender lorises of different age-sex categories are reported in this paper.

METHODS

The study site, locally called Beerangi Karadu lay in the Ayyalur Forest Range (SINGH et al., 1999) roughly at 10°29'N and 78°10'E, at an altitude of 400 m asl (Fig. 1). It included 16 ha of open dry scrub jungle. The country road that connected the village of Ayyalur to the town of Natham ran through the study area. On one side of the road the land rose up in a hill; the tree species here were mainly Acacia, Euphorbia, Azadirachta, Albizia, and Cassia. Although this was legally a Reserved Forest area, tree felling was a common practice. The land on the other side of the road was taken up by a Tamarindus and Eucalyptus orchard and fields bordered by Cocos nucifera. There was little canopy cover or contiguity in this part of the study area. Prosopis, Commiphora, and Azadarichta, overgrown with lianas, formed a natural fence for the orchard along the roadside; this area was extensively used for ranging by slender lorises.

The study began in October 1997 and concluded in June 1999. Observations were conducted on foot every night from dusk to dawn (18:00 to 06:00). Animals were first spotted by their orange-red tapetal reflection to light and then followed using red cellophane paper-covered Petzl headlamps (Petzl, Crolles, France), as has been recommended earlier (CHARLES- DOMINIQUE, 1977; CHARLES-DOMINIQUE & BEARDER, 1979). Twenty-eight study animals were individually identified during the course of the study. However, sufficient data to calculate home ranges was available for only 16 of them.

Tree pathways were flagged and particular trees that were most often used by the animals were tagged during the course of nightly observations. This made it easier to record if different animals used the same pathways and trees, and the frequency of their usage. If a focal animal had been followed continuously from its sleeping site at dusk to its sleeping site at dawn, it was considered a Full Night Follow. A focal animal follow that did not last the whole night, but included more than five continuous hours was considered a Partial Night Follow. In the morn- ing after a Full Night Follow, the Path Length and distance traversed by the animal during the night was measured, and the night range plotted. Path Length was defined as the distance cov- ered by the focal animal once during the course of the night. Night Distance was defined as the total distance travelled by the focal animal during the course of the night i.e. the Path Length together with distances that the animal repeatedly covered. For instance, if a focal animal trav- elled from its sleeping site (point A) to a tree 50 m distant (point B), remained there the whole night, and moved back to the sleeping site (point A) at dawn, then its Path Length would be 50 m (A to B) and the Night Distance would be 100 m (A to B to A).

Ad lib sampling and 5-rain instantaneous sampling techniques (AL'rMANN, 1974; ANONYMOUS, 1981) were employed to record the behavioural categories of an animal as it was followed through the night. Apart from behavioural variables, every instantaneous scan of a focal individual also included its Sighting Point. The term Sighting Point was used to describe the geographical location of a study animal when it was seen in a particular scan. At the end of the entire study period, the matrix of all the Sighting Points of an animal were plotted and the length of the straight lines connecting the outermost Sighting Points were physically measured using a tape measure and compass. The Home Range of an animal has been defined as the entire area used by it during the study period, and hence, comprised the area enclosed by the

Slender Loris Home Range 239

N

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straight lines connecting the outermost Sighting Points of this animal. The area within the Home Range used more intensively by the animal was designated as its Core Area. This has been defined as the area enclosed by straight lines joining the Sighting Points where the animal was seen in at least 15% of its scans. Fifteen percent was chosen as the lower limit because from the total number of Sighting Points and the number of scans conducted on all the study animals, it was calculated that, on an average, a study individual should be probabilistically seen at each of its Sighting Points in 7% of its scans. Core Area calculations were not carried out for the subadults and juveniles due to insufficient data. The straight lines involved in deter- mining both Home Range and Core Area were represented on a graph sheet and the respective

240 S. RADHAKRISHNA t~ M. S1NGH

areas calculated graphically. Intersexual and Intrasexual Overlap in Home Ranges between dif-

ferent individuals were estimated similarly. Three indices have been used to analyze Intersexual Overlap in Home Ranges. The A Index,

represented in hectares, is the actual area of female Home Range that was overlapped by a male Home Range. The B Index, represented as a percentage, is the proportion of the total Home Range of a female that was overlapped by a male Home Range. Since the Home Range of a male overlapped with those of more than one female, a third index - the C Index - was devel- oped to test for the relative contribution made by the Home Range of a particular female to the total overlapping displayed by the Home Ranges of all the females. This index, represented as a proportion, is calculated as

Percentage overlap of a particular female 's Home Range

Sum of the percentage overlap of all the females ' Home Ranges.

Four main age categories were recognized in the study individuals for the purpose of evaluat- ing Home Range differences with respect to age. These were the Early Juvenile - during the pre-weaning period from birth to 5 months of age, the Late Juvenile - during the post-weaning period from 5 to 9 months of age, the Subadult - from 9 to 12 months of age, and Adult - beyond 12 months of age. These age categories have been devised on the basis of the physical and social development of the animal (RADHAKRISHNA, 2001).

Non-parametric tests (Mann-Whitney U-test, Wilcoxon 's matched pairs signed ranks test and Kendall ' s rank correlation test) were employed to check for significant differences and correla- tion in Home Range sizes with respect to the sex and age classes of the study individuals (SOKAL • ROHLF, 1995). All tests were performed using the statistical software programme

Statistica, Version 4.5.

RESULTS

HOME RANGES OF ADULT INDIVIDUALS

Home Ranges and Core Areas were calculated for four adult males and four adult females. Table 1 gives the information on identity, hours of observation, and Home Ranges for each of these individuals. The mean (-q- SD) female Home Range area was 1.12 (4- 0.33) ha, while the mean female Core Area was 0.15 (-t- 0.05) ha. The mean Home Range size of a male was 2.36

(-q- 0.73) ha and the mean Core Area size was 0.37 (-+- 0.16) ha.

Table 1. Home ranges and Core Areas of adult individuals.

Identity of animal GA TI MO IN DO BI AK SU

Home Core Age-sex Hours of Number Nights followed range Area class Period of study observation of scans P F (ha) (ha) Ad female October 5, 1998-June 12, 1999 85 530 3 3 0.87 0.08 Ad female December 2, 1997-June 22, 1999 194 1613 15 2 1.57 0.16 Ad female February 16, 1998-June 23, 1999 133 1324 8 3 0.87 0.15 Ad female April 26, 1998-June 25, 1999 19 85 1 - 1.17 0.21 Ad male January 8, 1998-April 3, 1998 45 436 3 - 1.92 0.45 Ad male April 13, 1998-May 10, 1999 30 272 1 - 3.32 0.55 Ad male September 5, 1998-June 22, 1999 74 498 1 3 2.52 0.25 Ad male June 24, 1998-June 14, 1999 29 222 1 - 1.67 0.22

Ad female: Adult female; Ad male: Adult male; P: Partial night follow; F: Full night follow.

Slender Loris Home Range 241

The Home Range size of a male was significantly larger than the Home Range size of a female (Mann-Whitney U-test: n = 4, 4; Us = 0; p < 0.05) and the male Core Area was signifi- cantly larger than the female Core Area (Mann-Whitney U-test: n = 4, 4; Us = 0; p < 0.05). However, the percent values for Core Area of total Range were almost similar in both the sexes (15% in the females and 14% in the males).

The mean Path Length of an adult female was 119 (-I-27.37) m with a range of 75 - 157 (n = 6). The mean female Night Distance was 234 (-q- 65.08) m (range: 155 - 338, n = 6), twice the mean female Path Length value. The mean Path Length of an adult male was 241 ( - - 40.31 ) m with a range of 209 - 294 (n = 4). The mean male Night Distance was 328 (-+- 112.73) m (range: 240 - 478, n = 4), 1.36 times the mean male Path Length value. The male Path Length was significantly larger than the female Path length (Mann-Whitney U-test: n = 4, 6; Us = 0; p = 0.01). Night Distance values did not differ significantly between the sexes.

INTRASEXUAL HOME RANGE OVERLAP

Adult females had very little overlap in their Home Ranges; the mean female Home Range overlap was 0.043 (___ .01) ha (range: 0.028 - 0.053, n = 3), and none at all in their Core Areas (Fig. 2). Among the adult males, a larger mean intrasexual Home Range overlap of 1.29 ( - - 0.77) ha (range: 0.54 - 2.07, n = 3) was observed. Though one male range overlapped at least two other male Home Ranges, there was no overlap in their Core Areas (Fig. 3).

INTERSEXUAL HOME RANGE OVERLAP

The mean male-female Home Range overlap among the study animals was 0.73 (+0 .34) ha (range: 0.33 - 1.30, n = 10). The Home Range of an adult male overlapped the Home Ranges of at least two females. Male Core Areas also overlapped female Core Areas, which were usually around sleeping sites and parking trees. Among the study animals, it was observed that though a male's Home Range overlapped the Home Ranges of two or three females, there was a greater overlap with a particular female's range than with those of the others (Table 2).

HOME RANGES OF JUVENILES AND SUBADULTS

Home Ranges were calculated for eight juvenile and subadult individuals, all of which were offspring of the study females (Table 3); these have been depicted in Figure 4. Identification of mother-offspring pairs was possible since the females were observed to be pregnant and were later seen carrying their respective offspring. Infants were parked when they were 3 weeks old and weaned by about 5 months of age (RADHAKRmHNA, 2001). Home Ranges distinctly increased post-weaning. The pre-weaning Home Range of 0.14 ( _ 0.08) ha was significantly smaller than the post-weaning Home Range of 0.70 ( - - 0.30) ha (Wilcoxon's matched pairs signed ranks test, n = 7, Ts = 0, p < 0.05).

The mean Path I~ngth during the pre-weaning stage was 42 ( _ 30.62) m (range: 5 - 145, n = 49) and the mean Night Distance 104 (-q- 62.75) m (range: 13 - 280, n = 49). The mean pre- weaning Night Distance was 2.5 times greater than the Path Length during the same period. The mean Path Length during the post-weaning stage was 105 ( _ 46.78) m (range: 40 - 231, n = 45) and the mean Night Distance 255 (+__ 85.45) m (range: 130 - 500, n = 45). Again, the mean post-weaning Night Distance was 2.4 times more than the mean post-weaning Path Length. The pre-weaning Path Length and Night Distance were significantly smaller than the post-weaning Path Length and Night Distance (Mann-Whitney U-test: n = 49, 45; Path Length: Us = 216; p < 0.01; Night Distance: Us = 162.50; p < 0.01).

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The mean subadult Home Range was 0.97 (-I- 0.16) ha, with a range of 0.80 - 1.12 (n = 3). The mean subadult Path Length was 116 (-I- 39.57) m (range: 50 - 65, n = 12) and the mean Night Distance 244 (-I-- 31.66) m (range: 18 - 290, n --- 12). The mean subadult Night Distance was twice the mean subadult Path Length. Until the age of 10 months, individuals ranged within their mother 's range. Those older than 10 months either moved out of the study area (subadult female AN), or began to enlarge their ranges by including areas outside the mother ' s range (subadult females IS and PU). Three percent (0.03 ha) of subadult female IS' Home Range lay outside her mother 's Home Range, while 37% (0.41 ha) of subadult female PU' Home Range lay outside her mother 's Home Range.

Slender Loris Home Range 243

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No significant correlation was found between the size of the offspring' Home Range and that of the mother's Home Range (Kendall's rank correlation: n = 6; ~" = 0.24; p > 0.05). The

Table 2. Male-female Home Range overlap.

Identity of Female T I (HR = 1.57 ha) Female 1 N (HR = 1.17 ha) Female M O (HR = 0.87 ha) adult male A (ha) B (%) C (prop) A (ha) B (%) C (prop) A (ha) B (%) C (prop)

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subadult female Home Range was not significantly different from the adult female Home Range (Mann-Whitney U-test: n = 3, 3; Us = 4; p > 0.05). The female subadult Path Length and Night Distance were also not significantly different from those of the adult females (Mann-Whitney U-test: n = 12, 6; Path Length: Us = 35; p > 0.05; Night Distance: Us = 30.5; p > 0.05),

DISCUSSION

The slender loris Home Range sizes described in the present study differ from the figures

246 S. RADHAKRISHNA & M. SINGH

reported in earlier studies. This can be partly ascribed to the difference in the subspecies involved and their environments; the JOHNSON (1984) and KAR GUPTA & NASH (2001) studies were on the wet forest malabaricus subspecies. The differences with the NEKARIS (2000) results, which were obtained from the same study site, can be attributed to the different method- ologies used and the longer duration of the present study.

The basic pattern of home ranges in many nocturnal mammals i.e. variable overlap in female home ranges, little overlap in male ranges, and male-female range overlap, is apparently a prim- itive feature of placental mammals (CHARLES-DOMINIQUE, 1977). CHARLES-DOMINIQUE and BEARDER (1979) observe that in most lorisid species, the system of social organization is based on the relationships between individual home ranges. On this basis, i.e. the amount of inter and intrasexual home range overlap shown by the species, BEARDER (1987) has classified the social systems of nocturnal primates into five categories. The results of this study show that the slen- der loris home range pattern involves minimal intrasexual overlap in female ranges, large intra- sexual overlap in male ranges, male ranges larger than female ranges and large intersexual home range overlap. Hence the species does not fall wholly into any one of BEARDER'S (1987) categories. Instead they show features common to Type I and Type II of the classification. Type I social systems are distinguished by adult male ranges being larger than adult female ranges, intersexual and intrasexual home range overlap and the presence of matriarchies. In Type II social systems, adult male ranges are larger than adult female ranges, and intersexual range overlap exists, while intrasexual range overlap and matriarchies are absent. Like most of the galagos, which have been categorized as Type I, slender lorises have overlapping male and female ranges, with male ranges bigger than the female ranges, and intrasexual overlap in the male ranges. But the lack of female matriarchies and minimal overlap in female ranges is more akin to the potto social system (Type II). Though a slender loris subadult female shared the Home Range with her mother for some time, soon either the daughter emigrated or, as observed in RADHAKRISHNA (2001), the mother departed leaving the Home Range to the daughter. Similarities can also be seen with the aye-aye ranging pattern, where male ranges show large intrasexual overlap and female ranges minimal intrasexual overlap (STERLING, 1993).

Owing to the fact that overall individual home ranges were measured at the end of the study period, possible seasonal changes in home ranges were not taken into account. Hence it has not been possible to compare if the intersexual home range size difference holds true with respect to seasonal variation too.

The Path Length-Night Distance relation differs between slender Ioris males and females. In females, the Night Distance is twice the Path Length. This shows that females usually returned to the same sleeping sites. In males on the other hand, the Night Distance is 1.36 times the Path Length. This means that males changed their sleeping sites more often than the females. The reason for this could be that slender loris males based their sleeping sites on the sleeping sites of the different females whose ranges they overlapped. Also, though a male range overlapped the ranges of at least three females, more area of a particular female's Home Range was used by the male. These points appear to indicate that the distribution of slender loris male ranges was dic- tated by the location of female ranges. Such a phenomenon is not unusual. The fundamental paradigm of socio-ecology states that whereas the spatial distribution and social relationships among females reflect ecological conditions, the distribution of males and the social relation- ships among them are determined by the spatio-temporal distribution of mating opportunities (EMLEN & ORIN6, 1977). BEARDER (1987) observes that in Galago senegalensis the distribution of the male ranges is strongly influenced by the distribution of the female ranges and male range size bears no obvious relationship to environmental resources.

The increase in Path Length and Night Distance and size of Home Range post weaning can

Slender Lofts Home Range 247

be attributed to the need of the individual to now depend fully on the resources of the habitat to fulfill nutritional requirements. Size of the mother ' s Home Range does not appear to signifi- cantly affect size of offspring' Home Range. We hypothesize that factors like age and sex of the individual, twin/singleton status at birth, survival of twin and quality of habitat play important roles in determining Home Range size among the juveniles and subadults. However data was insufficient to calculate the relative significance of any one of these factors.

Female subadult and female adult Home Range, Path Length, and Night Distance values do not significantly vary. This would mean that a subadult slender loris female attains the ranging pattern of an adult female. However this conclusion is based on the small sample size of this study; a larger sample size would give more robust results.

Acknowledgements. This work was supported by a UGC (University Grants Commission, India) fellow- ship and private donors. We are grateful to all those who helped us complete this work, in particular S. THEODORE BASKARAN, CREA-RAMAKRISHNAN, ANNA NEKARIS, HELGA SCHULZE, SIMON BEARDER, TAB RASMUSSEN, ANINDYA SINHA, members of CRAB, FRO Rajagopal and field assistants Santiago and AsH. We thank the Chief Wildlife Warden, Tamil Nadu for official permission to work in the Reserved Forest of Ayyalur and the reviewers of this paper for their suggestions.

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248 S. RADHAKRISHNA & M. SINGH

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- - Received: March 31, 2001; Accepted: May 3, 2002

Authors' Names and Present Addresses: SINI)HU RADHAKRISHNA, National hlstitute ~[ Advanced Studies, hzdian h~stitute of Science Campus, Bangalore 560 012 Karnataka, h~dia, e-mail: Ioris_sr@yahoo.com; MVWA S[NGH, Department of Psychology, University t~f Mysore, Manasagangotri, Mysore 570 006, Karnataka, hldia, e-mail: mewasingh @ sancharnet .in