Hylobates muelleri Martin 1841

8. Muller’s Gibbon Hylobates muelleri French: Gibbon de Miller / German: Mller-Gibbon / Spanish: Gibon de Muller Other common names: Bornean Gray Gibbon, Gray Gibbon, Miller's Bornean Gibbon, South Bornean Gray Gibbon Taxonomy. Hylobates muelleri Martin, 1841, Indonesia, Kalimantan. Restricted by M. Lyon in 1911 to south-eastern Borneo. Until recently, H. funereus and H. abbotti were recognized as subspecies of H. muelleri, but morphologically and genetically they are clearly distinct species. H. mueller: hybridizes with H. albibarbis in the upper Barito watershed in central Borneo. This hybridization is evidently old (5000-10,000 years), and the hybrid zone covers about 5000 km?, which for some is argument that H. albibarbis and H. mueller should be considered conspecific. A population living in east-central Kalimantan may prove to be a morph or a distinct subspecies. There are wide intergrade zones between H. mueller, H. funereus, and H. abbotti where their ranges meet. Monotypic. Distribution. Borneo, SE Kalimantan, approximately S of the Mahakam River and E of the Barito River. Descriptive notes. Head-body 40-8 cm; weight 5.6-8 kg (males) and 4.6-6.2 kg (females). The pelage of Miller's Gibbon is either mouse-gray or brownish in color. These gibbons have a dark cap, face, and chest which varies in extent individually and with age, becoming more extensive in older individuals. Males differ from females by having a pale, often incomplete,facial fringe and a dark brown (as opposed to black) crown. The crown hair is directed fanwise from the front of the scalp and is markedly elongated over the ears. Habitat. Primary and secondary semi-deciduous monsoon, dipterocarp, and tropical evergreen forest. Miller's Gibbons can tolerate a degree of selective logging if sufficient tall, fruit-bearing trees remain. Hybrid H. mueller: x H. albibarbis (Bornean Whitebearded Gibbon) have been studied by K. McConkey at Barito Ulu, in the Barito River watershed, Central Kalimantan, where the terrain is described as rugged (hilly to mountainous). There, dipterocarp forest predominates, interspersed with heath forest. The dry season is from July to September and the wet season is between October and January, with a mean annual rainfall of 3738 mm. Food and Feeding. The study in Barito Ulu focused on the composition of the diet, and aspects of seasonality, food selection, and seed dispersal. Over a year, non-fig fruits were the most common items eaten, followed by young leaves, and figs and flowers; only very small numbers of insects were recorded. The diet in terms of these plant parts varied during the year. Fig trees can fruit throughout the year and figs were eaten according to their availability. Other fruits were more predictably seasonal. Fruits were available year round, but peaked in abundance and diversity in March-May. Flowers peaked in abundance in January-February and again in September, and the gibbons evidently favored them. Flowers were the strongest predictor of what the gibbons would eat in a given month. When they were abundant, they would increase their visits to flowering trees and reduce the time spent eating fruit. Overall the diet of two groups during one year was 62% fruit (52-7% ripe fruit and 9-3% unripe fruit and seeds), 23-8% young leaves, 13-4% flowers, and 0-8% insects. In all, 54-7% of the fruits were of trees, 27-3% were from lianas, 17-3% were figs, and 0-7% were from parasites and epiphytes. Fruits were taken from c.167 species. An analysis of selection ratios for different fruit types showed that they preferred medium-size (6-30 g), yellow-orange fruits with a juicy pulp and a thin or rind-like skin, in dense but small crops. They avoided purple-black and red fruits with softdry pulp, many-seeded fruits in sparse crops, and fruits with large seeds (more than 20 mm wide). They did not eat fruit with seeds larger than 40 mm in width. They were most selective when they could afford to be, when fruits were abundant. Fruits of Gnetum microcarpum (Gnetaceae) and Cryptocarya crassinervia (Lauraceae), Erycibe maingayi (Convolvulaceae), and Diospyros puncticulosa (Ebeneaceae) were found to be important when fruit was scarce. The gibbons dispersed seeds by endozoochory (ingestion and defecation) of 81% of the fruits (90% of the liana species, 72% of the tree species) that they ate (others were unripe, destroyed, or dropped). More than 90% of the seeds were defecated more than 100 m from the parent tree (the mean was more than 300 m and the maximum was 1000 m), and feces (and seeds) were scattered as they fell to the forest floor—aspects considered favorable for the seeds. Breeding. There is no specific information available for this species, but aspects of breeding will be very similar to the East Bornean Gray Gibbon (H. funereus). Activity patterns. Miiller’s Gibbons are diurnal and arboreal. Movements, Home range and Social organization. Two groups studied at Barito Ulu comprised a single adult pair with a subadult and a juvenile or infant. They occupied home ranges of 43 ha and 46 ha. About 88% of the home range is defended as a territory for the exclusive use of the resident group. Although generally monogamous, polygynous pairings have been reported in the H. muelleri x H. albibarbis hybrid zone. Other aspects of their social organization and ranging are probably very similar to the East Bornean Gray Gibbon for which some information is available from the study of D. Leighton at Kutai National Park. Status and Conservation. CITES Appendix I. Classified as Endangered on The IUCN Red List (as H. m. mueller). Miiller’s Gibbons are protected under Indonesian law and occur in three protected areas: Sultan Adam Forest Park (South Kalimantan Province), Kersik Luwai National, and Sungai Wain Protection Forest Park (both in East Kalimantan Province). This speciesis generally common. Deforestation (most recently for oil palm plantations), logging, hunting, and trade in illegal pets are the principal threats. The population density in Sungai Wain Protection Forest was estimated at 7-9-9-5 ind/km? A population estimate for Miiller’s Gibbon does not exist, but the population of “gray gibbons” (Miiller’s, East Bornean Gray, and Abbott's Gray, H. abbotti, gibbons) has been estimated at 250,000-375,000. Bibliography. Bartlett (2007), Brody & Brody (1974), Chivers (2001), Geissmann (1991a), Geissmann & Nijman (2008d), Groves (2001), Haimoff (1985a), Haraway et al. (1988), Hirai, Hayano et al. (2009), Hirai, Wijayanto et al. (2005), Kloss (1929), Leighton (1987), Lyon (1911), Maples et al. (1988), Marshall & Sugardijito (1986), Mather (1992), McConkey (2000, 2005a, 2005b, 2009), McConkey, Aldy et al. (2002), McConkey, Ario et al. (2003), Meijaard et al. (2005), Mitani (1984, 1985b, 1985c), Nijman (2005), Oka & Takenaka (2001), Rodman (1978), Schultz (1933), Short (2004), Sody (1949), Stott & Selsor (1961), Tenaza (1985), Van Ngoc Thinh, Mootnick, Geissmann et al. (2010), Yasuma & Andau (2000).Published as part of Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Hylobatidae, pp. 778-791 in Handbook of the Mammals of the World – Volume 3 Primates, Barcelona :Lynx Edicions on page 784, DOI: 10.5281/zenodo.672795