Spacing System of the Mysore Slender Loris (Loris Lydekkerianus Lydekkerianus)
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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 121:86–96 (2003) Spacing System of the Mysore Slender Loris (Loris lydekkerianus lydekkerianus) K.A.I. Nekaris* Department of Anthropology, Washington University, St. Louis, Missouri 63130 KEY WORDS Lorisidae; Strepsirrhini; nocturnal prosimian; home range; sleeping site; social system ABSTRACT Loris lydekkerianus lydekkerianus has cated within 1.9 ha in the center of the study area. The been shown to have a promiscuous copulatory pattern, to minimum convex polygon in hectares encompassing each maintain social networks via frequent loud calls, to inter- animal’s range was determined, as well as overlap among act socially throughout the night with all age classes, and home ranges of individual lorises. Average home range to sleep socially. Though these behaviors point towards a sizes were: adult males, 3.6 ha Ϯ 0.09; subadult/smaller multimale social system, no study of their spacing system males, 1.17 ha Ϯ 0.26; and adult and subadult females, has yet been provided to support this view. From October 1.59 ha Ϯ 0.24. Male ranges overlapped with at least 2–3 1997–August 1998, I conducted a study of the Mysore other adult males (0.72 ha Ϯ 0.23). Female ranges over- slender loris in Ayyalur, India. During 1,400 field hours, lapped slightly with at least 2 other female ranges (0.22 data were collected on range use of 3 adult females, 3 ha Ϯ 0.25). Male ranges overlapped those of at least 3 adult males, 1 subadult female, and 1 subadult male. females (0.82 ha Ϯ 0.51). Patterns of home range and Lorises slept in groups averaging 4 individuals, composed sleeping site support previous suggestions of a multimale of an adult female, her offspring, and 1–2 adult and social system, similar to aye ayes and some galagos. Am J subadult males. Sleeping sites for three groups were lo- Phys Anthropol 121:86–96, 2003. © 2003 Wiley-Liss, Inc. The slender loris (genus Loris) is a small noctur- though there is strong evidence that male and fe- nal prosimian primate endemic to Sri Lanka and male potto pairs sleep more often in close proximity South India. Only recently have we begun to under- to each other than to other pairs (Pimley, 2003; stand its behavior and ecology in the wild (Kar Pimley and Bearder, in press). Potto sleeping sites Gupta, 1995; Nekaris, 2000, 2001a,b, 2002; consist of tangled branches rather than tree hollows, Radhakrishna, 2001; Nekaris and Jayewardene, and are changed often. The sleeping sites of the 2002). The slender loris is a member of the subfam- smaller-bodied angwantibo (A. calabarensis) con- ily Lorisinae (Anonymous, 2002), which includes sisted of tangled vines and branches. Neither pottos four extant genera, Perodicticus and Arctocebus nor angwantibos regularly (if ever) emit loud calls from Africa, and Nycticebus and Loris from Asia. throughout the night, and rarely come together in These animals share a remarkable suite of morpho- social interactions (Jewell and Oates, 1969; Charles- logical traits, related to a unique nonsaltatory loco- Dominique, 1977; Pimley, 2003). A recent study of motor pattern (Osman Hill, 1953; Walker, 1969; slow lorises found they almost always slept alone, Sellers, 1996). This locomotor pattern is said to limit with the most common dyad being a mother and their ability to move over a relatively large area in a given night. It is also said to limit frequent encoun- ters with conspecifics, as animals may be too slow to Grant sponsor: One with Nature, Philadelphia Zoo; Grant sponsor: meet often in the night, or to return to a communal Sophie Danforth Conservation Biology Fund; Grant sponsor: Primate sleep area before dawn (Charles-Dominique, 1977, Conservation, Inc.; Grant sponsor: Bruce Wulff; Grant sponsor: Wen- 1978; van Schaik and van Hoof, 1983). In association ner-Gren Foundation; Grant sponsor: NSF; Grant number: with other behaviors, such as emitting no loud calls, SBR-9714870. and interacting infrequently via physical social con- *Correspondence to: Dr. Anna Nekaris, Nocturnal Primate Re- tact throughout the night, the lorisines as a whole search Group, School of Social Sciences and Law, Oxford Brookes have been described as highly cryptic (Sussman, University, Oxford OX3 OBP, UK. 1999). E-mail: [email protected] Research conducted on the potto, angwantibo, and slow loris have until now supported this view. In Received 11 August 2000; accepted 2 August 2002. both African lorisines, sleeping congregations con- DOI 10.1002/ajpa.10189 sisted of single animals, or mothers and their off- spring. These species almost always slept alone, © 2003 WILEY-LISS, INC. MYSORE SLENDER LORIS RANGING 87 infant. Sleeping sites were found in branch tangles tern of range overlap exhibited by these species, or rather than tree hollows. They also never made loud spacing system. Because many nocturnal prosimian calls during the night (Wiens, 2002). species are studied only with the aid of radio track- This view that lorisines as cryptic and almost ing, the intricate pattern of range overlap becomes completely solitary has been contrasted to the fact central to understanding their social organization that closely related, similarly sized bushbabies that (Sterling et al., 2000). do include leaping and obvious speed in their loco- Bearder (1987) used differences in spacing and motor repertoire form cohesive sleeping groups of range overlap to characterize five social categories 2–7 animals and produce loud contact calls through- based on 15 species of nocturnal prosimians. Pat- out the night. Some species (e.g., Galago moholi, terns of range overlap included: type 1, females over- Galago zanzibaricus) also spend up to 20% of their lap with other usually related females, and one or time in gregarious social activity, unlike the 2–4% of two larger male home ranges overlap those of sev- the majority of nocturnal prosimians (Bearder, eral females (e.g., Galago moholi); type 2, male 1987; Sussman, 1999). ranges are larger than female ranges and may over- The slender loris is different from other lorisines lap more than one female range, though same sex in many respects. First, slender lorises have been ranges overlap very little if at all (e.g., Perodicticus seen to move quickly in many contexts, to engage in potto); type 3, ranges of individual males and fe- short jumps, and even to run (Nekaris, 2001a; Nek- males coincide (e.g., Tarsius bancanus); type 4, an- aris and Jayewardene, 2002). They do produce a imals are almost fully solitary, with only some over- loud call throughout the night, at a rate similar to lap of male ranges with female ranges at range that of bushbabies or even more frequent than them borders (e.g., Mirza coquereli); and type 5, males, (Bearder et al., 2002). They also frequently engage females, and their offspring forage together as a in gregarious social behaviour, in contrast to other cohesive group (e.g., Eulemur mongoz). A study of species of nocturnal primates. Slender lorises in In- the aye-aye (Daubentonia madagascariensis) re- dia (L. l. lydekkerianus) were found to be social for vealed an additional pattern (type 6) where males more than 18% of their activity budget, with some overlap with one another, and with many females animals seen in association with others for more ranges, though female ranges do not coincide (Ster- than 50% of their activity budget. (Bearder et al., ling, 1993). 2002; Nekaris, 2001a, 2002; Nekaris and Rasmus- More recently, Mueller and Thalmann (2000) re- sen, 2003). Slender lorises (L. l. nordicus and L. duced these types to four patterns of relations, link- tardigradus tardigradus) in Sri Lanka were ob- ing them to social system: 1) The home ranges of a served in contact with other animals for more than male and just one female coincide (ϭ monogamy). 2) 40% of their activity budget (Nekaris and Jayewar- The home range of a male overlaps several females, dene, 2002). These social interactions occurred be- and vice versa (ϭ multimale system). 3) The home tween adult males and females, and between adults range of a male overlaps those of several females and youngsters, but rarely between adults of the exclusively (ϭ harem). 4) The home range of a fe- same sex (Nekaris, 2001a,b, 2002; Nekaris and male overlaps those of several males (ϭ polyandry). Jayewardene, 2002; Radhakrishna, 2001). Slender Through this standard classification system, it will loris mating in the wild also is a highly social event, be possible to compare and understand the variation with up to 5 males pursuing a single female in in nocturnal primate social systems in a broader estrous, followed by multiple prolonged intromis- perspective. sions between a single female and male (Nekaris, The above categories are based mainly on behav- 2001b; Radhakrishna, 2001; Nekaris, 2002, 2004). ioral studies of the Galaginae, Lemuriformes, and Based on a similar copulation pattern in captivity, Tarsiiformes. However, very little is known about Dixson (1995, 1998) predicted that lorises might spacing patterns among any of the lorisines. A long- have a multimale mating system. term study of the potto (Perodicticus potto) showed These marked differences from other lorisines and that the home ranges of males overlapped those of at similarities to the galagines might also be expected least two females (Bearder’s type 2) (Charles-Do- to be reflected in their ranging patterns and social minique, 1974). Home-range size of females was system. It is now widely accepted that a diverse about 7.5 ha, and of males, 9–40 ha. Little is known range of social systems are evident among nocturnal about range overlap of the angwantibo (Jewell and prosimians, and the description of this variability Oates, 1969; Charles-Dominique, 1977). has been the topic of numerous recent papers (e.g., Some success has been achieved in assessing Bearder, 1987; Sterling and Richard, 1995; Mueller range overlap in the Asian slow loris (Nycticebus and Thalmann, 2000; Sterling and Radespiel, 2000).