A Multi-Male Situation in a Population of Predominantly Unimale Bisexual Troops of Hanuman Langurs, Semnopithecus entellus , Around Jodhpur, Rajasthan

摘要

The Hanuman langur ( Semnopithecus entellus Dufresne, 1797) is the best studied and most adaptable South Asian colobine. It ranges over a variety of habitats from sea level to the Himalayas (~ 4,000 m altitude) and from moist deciduous forest to scrub and open rocky areas, such as Jodhpur (Jay, 1963; Oppenheimer, 1977; Vogel, 1977; Roonwal & Mohnot, 1977; and Wolfheim, 1983). Besides its remarkable adaptability, this species has a variable social organization. The two basic types of social units are bisexual troops and all-male bands. Troops are matrilineal groups of adult females and their offspring, with either one adult male (unimale bisexual troops) or more than one adult male (multi-male troops). In the western part of their habitat, these langurs usually form one-male bisexual troops (harems). The segregated males live in all-male bands with no possibility of reproduction. The percentage of one-male troops versus multi-male troops, and the corresponding number of males in all-male bands, vary from site to site (Newton, 1988). Hanuman langurs exhibit clear-cut sexual dimorphism. On average, adult males weigh 18.5 kg and adult females weigh 11.7 kg (Sommer 1985). Males defend infants but never carry or feed them. Multi-male bisexual troops are very rare in the Jodhpur area. Each troop has a home range of about 0.5–1.3 km2. The home ranges of multi-male bisexual troops are larger than those of unimale-bisexual troops. Females remain for life in their natal troops, but males emigrate, usually as juveniles, to unisexual all-male bands, whose home range can be as large as 20 km2 (Rajpurohit, 1987; Rajpurohit & Sommer, 1993; Rajpurohit et al., 1994). As multi-male bisexual troops form, males migrate from their troops and, after some time, return. The ranging area of these males is also larger in comparison to alpha males and females. The multi-male troop is created in two ways: first, when male juveniles stay in their own troop and alpha males have no objection and don’t try to chase them out; and second, when an outside male or group of males comes to take over the bisexual troop and a multi-male situation arises. Such a situation may go on for a few months to more than a year. In Jodhpur langurs, a multi-male troop structure may develop during an alpha male change, but that is usually temporary, and the troop becomes one-male again. There have been some cases observed where troops developed semi-permanent multi-male structures (Srivastava, et al., 1986; Mohnot, et al., 1987; Rajpurohit, 1987). In the multi-male societies of red colobus ( Procolobus ) and Himalaya Hanuman langurs, the dominant adult males achieved the most mating and presumably therefore sired the most offspring (Struhsaker, 1975; Boggess, 1980). However, Laws & Laws (1984) found that in the Himalayan foothills, Hanuman langur males, temporarily immigrating into bisexual troops, were as successful at mating as the alpha. In matrilineal, multi-male colobine societies, there is little affiliative social contact among adult males. Within multi-male troops of Himalayan Hanuman langurs, agonistic vocal interaction occurs between males much more frequently than between females. Boggess (1980) found that only 0.3% of adult grooming interactions were between males. Dunbar (1988) suggested that in Ethiopian Colobus grereza there is a higher frequency of agonistic interactions in multi-male troops than in unimale troops.