Mountains and swamp forests of Sumatra

Symphalangus s. syndactylus appears to have a larger cranium, tooth row, and body than the mainland subspecies (Groves 1972). A shallow medial sagittal groove reaches nearly into the tip of the nose. The nose, although of course variable, has a long tapering point over the nostrils (A. Mootnick prelim. obs.) (Figs. 7 and 8).

Figure 7.

Symphalangus s. syndactylus (Sumatran siamang) adult female “Ebony”, Twycross Zoo, England. Photo by Rod Williams.

Figure 8.

Symphalangus s. syndactylus (Sumatran siamang) adult female “Karenina”, GCC. Tapering of nose and medial sagittal groove. Photo by John Williams.

Northwest and central Malay Peninsula

The upper portion of the nose appears slightly bulbous, with an abbreviated midsagittal groove. The rounded internarial septum is separated dorsally by a slight constriction, and with a central latero-lateral depression, with a wide connection to the area above the lip. The lower half of the nose has a gradual tapering of the outer sides above the nostrils, with an increased tapering closer to the tip, giving the nose a slightly wider appearance on the lower portion than is observed in Symphalangus s. syndactylus (A. Mootnick prelim. obs.) (Fig. 9).

Figure 9.

Symphalangus syndactylus continentis (Malaysian siamang) adult male “Kino”, Close-up of the nose. Compare with Fig. 8. GCC. Photo by John Williams.

Northern Vietnam, between the Black and Red rivers, central Yunnan

Adult males, immature males and females have blackish hair. They have long body hair for Nomascus, and a few white hairs at the corner of the mouth (Fig. 14) (MCZ 38114–16). The hair of the adult females can range from buffish to a light tawny; they have a black-brown or black crown streak (Ma et al. 1988; Geissmann 1989). They have dark hair on the ventrum, that forms an inverted triangle (Geissmann 1995) (Fig. 15) and a small white patch of hair above the mouth and below the eyes. Adult females can also have black on the first digits, and chin, with a few black hairs on the genitals, pelvis, and legs, and around the ears. Individuals I have observed had a creamy-buff throat. Groves (2001, 2005) listed four subspecies of N. concolor. Besides the nominate subspecies and lu (see below), he included two forms from China, N. c. furvogaster (Menglai, Cangyan, Yunnan) and N. c. jingdongensis (Wenbu, Jingdong, central Yunnan) described by Ma and Wang (1986) but not dealt with in this review.

Figure 14.

Nomascus c. concolor (Tonkin black-crested gibbon) adult male “Zombie”, Twycross Zoo, England. Photo by Elliott Haimoff.

Figure 15.

Nomascus c. concolor (Tonkin black-crested gibbon) adult female “Hong-Hong”, Gejiu Zoo, China. 3 September 1990. Photo by Thomas Geissmann.

Northwestern Laos

Delacour (1951), with the help of J. Greenway and F. Edmond-Blanc, collected six specimens of N. concolor lu on 7 January 1939, at Ban Nam Khueng, northwestern Laos (20°23′ N, 100°15′ E; coordinates from Jenkins 1990). The exact collection date of the adult male holotype BMNH ZD1952.142 and an adult female paratype BMNH ZD1952.143 is confused in that the date on the specimen labels is 17, not 7, January 1939 (P. D. Jenkins pers. comm.). I am assuming that the error is with the specimen labels, since Delacour (1951) described all of the six specimens as being collected on 7 January 1939, which included the holotype.

Delacour (1951) provided the following description of two adult females. One female (MCZ 46288) has a black crown, with the overall pelage a vivid tawny (“fauve assez vif”), but strongly mixed with black hairs on the chest and abdomen. The second female, the paratype BMNH ZD1952.143, he described as having a black crown, with the overall pelage being a vivid tawny, but mixed with black hairs, perhaps due to a color transition (Delacour 1951).

There is some controversy concerning the description of Nomascus concolor lu, and even whether it still exists in its native habitat. During 2004–2006, however, I received correspondence from J.-F. Reumaux stating that 11 families of N. concolor lu had been located in the Bokeo Nature Reserve, northwestern Laos. There were also credible reports of a further seven families there. The existence of N. concolor lu in this reserve was confirmed through DNA extracted from feces (C. Roos pers. comm.), as well as by tape recordings, video footage, and photographs (Figs. 16 and 17). A video of a pair and infant in the reserve (Figs. 18 and 19) showed that they were very similar to two adult specimens at the MCZ (Figs. 20 and 21) that Delacour, Greenway, and Edmond-Blanc had collected on (I presume) 7 January 1939 at Ban Nam Khueng.

Figure 16.

Nomascus concolor lu (Laotian black-crested gibbon) adult female, Bokeo Nature Reserve. Photo permission: Jean-Francois Reumaux.

Figure 17.

Nomascus concolor lu (Laotian black-crested gibbon) immature, Bokeo Nature Reserve. Photo permission: Jean-Francois Reumaux.

Figure 18.

Nomascus concolor lu (Laotian black-crested gibbon) adult male, photo was reproduced from a video taken in the Bokeo Nature Reserve. Photo permission: Jean-Francois Reumaux.

Figure 19.

Nomascus concolor lu (Laotian black-crested gibbon) adult female and infant, photo was reproduced from a video taken in the Bokeo Nature Reserve. Photo permission: Jean-Francois Reumaux.

Figure 20.

Nomascus concolor lu (Laotian black-crested gibbon) adult male, MCZ 46289. Photo by Annie Lussier and Peter Weinberg, Museum of Comparative Zoology and Harvard University.

Figure 21.

Nomascus concolor lu (Laotian black-crested gibbon) adult female, MCZ 46288. Photo by Annie Lussier and Peter Weinberg, Museum of Comparative Zoology and Harvard University.

From my inspection of the adult female MCZ 46288, it is tawny-buff with a small black crown (Fig. 22), similar to that of the adult female with an infant in the video that was taken at the Bokeo Nature Reserve (Fig. 23). The upper chest is buff with a few black hairs, gradually darkening, with a black grizzling on the lower chest, abdomen, and genital region (Fig. 21), again similar to the adult female of the Bokeo Nature Reserve (Fig. 19). There is a brownish orange color in the center of the chest of MCZ 46288, possibly from her sternal gland (Fig. 21). There are a few black hairs on the fingers and toes. The chin is black (Fig. 21), with a few black hairs on the throat and above the ears. The face ring is slightly lighter than the surrounding hair. There are no long guard hairs. The female BMNH ZD1952.143 is much grayer in color than the female at the MCZ (P. D. Jenkins pers. comm.).

Figure 22.

Nomascus concolor lu (Laotian black-crested gibbon) adult female, MCZ 46288. Photo by Annie Lussier and Peter Weinberg, Museum of Comparative Zoology and Harvard University.

Figure 23.

Nomascus concolor lu (Laotian black-crested gibbon) adult female and infant, photo was reproduced from a video taken in the Bokeo Nature Reserve. Photo permission: Jean-Francois Reumaux.

Delacour's adult male MCZ 46289 is entirely black, with no white hairs at the corners of the mouth. It has short black body hair, mixed with longer black guard hairs. This contrasts with N. c. concolor males (MCZ 3811416) which have longer hair than N. concolor lu (MCZ 46289). The adult male co-type MNHN CG 1952-543 that Delacour collected on 7 January 1939 is also entirely black (C. Callou pers. comm.). Delacour's descriptions differ in that MCZ 46289 and MNHN CG 1952-543 are entirely black. Delacour indicated that all the males have at least a trace of gray on the cheeks.

With only a few museum specimens to examine, Groves (1972), Dao Van Tien (1983), and Marshall and Sugardjito (1986) described N. concolor lu as black, with a trace of silver along the side of the head. The adult male holotype BMNH ZD1952.142 has a trace of gray (or buff) on the cheeks and a small trace of gray on either side of the crown (P. D. Jenkins pers. comm.). The skin of a juvenile female USNM 296921 was collected by R. Elbel on 26 February 1953 at Khao Tham Phra. It had numerous incisions across the face (to remove the skull), which made it difficult to interpret. Rearrangement of the facial skin, however, showed that the juvenile, in black pelage, has a moderate amount of blackish hairs mixed throughout a narrow whitish-gray cheek patch, giving it an overall grizzled appearance. The narrow cheek patch begins below the ear, but not touching the ear, and ends above the chin, but not touching the lip. There are a few grayish white hairs throughout the pelage, including a few whitish hairs under the lip, and a few buff hairs in the genital region.

A topotype, AMNH 148262 labeled male, collected on 7 January 1939 at Ban Nam Khueng, is somewhat similar to the juvenile female USNM 296921. It has, however, a slight trace of a silver streak by the temples, and less silver hair on the facial cheeks. The genital area is blackish, with slight grayish grizzling on the rump. Although labeled as a male, AMNH 148262 has a very short pubertal tuft. As an adult male, the tuft should be longer, and the scrotal sack should be visible. An X-ray of the skull of this gibbon showed that the canines and lower third molars had not yet erupted (Fig. 24), and it is similar in this respect to a 4.9 yr old female Nomascus (GCC Parker). The nipples of AMNH 148262 are small, which is typical of immature male and female Nomascus (GCC Dexter and Parker). Geissmann (1989) also concluded that AMNH 148262 was a subadult female in the early stages of her color transition.

Figure 24.

Nomascus concolor lu (Laotian black-crested gibbon) subadult, AMNH 148262. Photo permission: Jean Spence, American Museum of Natural History.

Delacour (1951) wrote that the N. concolor lu holotype (BMNH ZD1952.142) male was overall black with a gray stripe over the eye to the ear. Delacour (1951) described three other males (MCZ 46289, MNHN CG 1952-543, and AMNH 148262) as having a slightly different appearance. Two of the three male N. concolor lu that he collected were in a black color phase, had a trace of gray on the cheeks, and a trace of gray on the loins. The third male (AMNH 148262 which appears to be a female) had a similar pattern of gray on the face as the holotype, but also a trace of gray on the cheeks, chin, and shoulders, upper thigh, and lumbar area (Delacour 1951). A somewhat similar description was given by Hill (1970) of an imported black juvenile gibbon (SDZ 024368) housed at the San Diego Zoo. It had large, white cheek-patches and white eye-patches. By 1971, the white eye-patches had faded into black (M. Jones pers. comm.). This, in some cases, is the final stage of the first color transition in Nomascus (Fig. 25). Hill's (1970) description was that of N. l. leucogenys (northern white-cheeked gibbon). Since N. l. leucogenys and N. concolor lu are found in bordering areas in northern Laos, some of the N. concolor lu museum specimens could be hybrids. Specimens may also be immatures undergoing color transitions, and even misidentified in their sex. DNA analysis is necessary to confirm their identity.

Figure 25.

Nomascus leucogenys siki (southern white-cheeked gibbon) adult female “Fany”, 1 year 10 month old male “Tai Chi”, Zoo Mulhouse. June 2004. Photo by David Gomis.

Northestern Vietnam, east of the Red River

Adult males, immature males and females have blackish hair with slightly brownish hair on the chest, extending sometimes from the throat to the abdomen (Figs. 26 and 27). It is difficult to interpret from the numerous photographs in Fischer (1965; see Fig. 26), whether “Patzi” had lighter-colored chest hair when in black pelage, or if her chest hair was sparse on pale skin. Adult females are buffish to buffish gray in color, which can be mixed with few longer blackish hairs. They have a long, wide, black crown streak that can extend past the nape, to the brow, tapering to a thin face ring, and becoming thicker at the chin (Fig. 28). The rectal hair is brownish. There are some black hairs above the ear. The vocalizations of an adult female (Patzi) in the Tierpark Berlin were similar to those of N. n. nasutus, but her pelage differed in that she had a very long, broad, black crown streak that went past the nape, and extended to the brow, tapering to a thin face ring and becoming thicker at the chin (Geissmann et al. 2000; Mootnick et al. 2006). This female had a narrow, blackish-brown chest plate slightly wider than the face, beginning at the throat and tapering at the top of the abdomen (Fig. 29).

Figure 26.

Nomascus n. nasutus (Cao Vit black-crested gibbon) juvenile female “Patzi” and juvenile male Nomascus leucogenys siki “Mohle”, Berlin Tierpark, Germany. 1963. Photo from archive of Tierpark Berlin.

Figure 27.

Nomascus n. nasutus (Cao Vit black-crested gibbon) infant female “Patzi”, Berlin Tierpark. 1962. Photo from archive of Tierpark Berlin.

Figure 28.

Nomascus n. nasutus (Cao Vit black-crested gibbon) adult female “Patzi”, Berlin Tierpark. August 1970. Photo from archive of Tierpark Berlin.

Figure 29.

Nomascus n. nasutus (Cao Vit black-crested gibbon) adult female “Patzi”, Berlin Tierpark. 1972. Photo from archive of Tierpark Berlin.

Hainan Island, China

Adult males have short black hair, and the crown hair is not as obvious as in other species of Nomascus (Fig. 30) (Pocock 1905; Groves 1972; Ma et al. 1988; Geissmann et al. 2000). Adult females have a black crown patch, brownish buff body hair, no black hairs on the limbs (Ma et al. 1988), and a small white patch of hair above the mouth and below the eyes (Fig. 31). Adult females have a thin, white face ring that is thicker above the mouth and below the orbital ridge (Mootnick et al. 2006). Comparison of the DNA of N. nasutus hainanus and N. n. nasutus may result in these two subspecies being elevated to species. Groves (2005) lists hainanus as a distinct species, and nasutus as a subspecies of N. concolor.

Figure 30.

Nomascus nasutus hainanus (Hainan black-crested gibbon) adult male, Hainan, China. Photo by Bawangling National Nature Reserve staff.

Figure 31.

Nomascus nasutus hainanus (Hainan black-crested gibbon) adult female and infant. Hainan. Photo by Bawangling National Nature Reserve staff.

Southern Yunnan, northern Laos, and northwestern Vietnam

The cheek patches of the adult male and immature connect under a black chin and can extend up to the top of the ear (Fig. 32). Adult females range in color from dark to light buff to creamy orange often diffused with tan, gray, or black hairs. They have a white face ring, and a small to medium-length black crown patch (Figs. 11, 12, and 32). Adult females can have reddish brown to brown-black hair in the genital region; black hairs on the tips of the fingers and toes; and white hairs below the eye and above the mouth. A trace of the crown patch can extend between the scapulae. The female has few black hairs around the ears. Females are sometimes larger than males.

Figure 32.

Nomascus l. leucogenys (northern white-cheeked gibbon) female left “Ricky”, male right “Vok”, GCC. Photo by Jim Zuckerman.

Central Vietnam and southern Laos

Nomascus l. leucogenys and N. leucogenys siki differ by a reciprocal translocation between chromosomes 1 and 22 not present in the former (Couturier and Lernould 1991). Groves (2001) pointed out that there is some difference of opinion as to whether the form siki was a subspecies of N. leucogenys or N. gabriellae. Two mtDNA studies placed it in a clade with leucogenys (Garza and Woodruff 1992; Zhang 1997), although it also evidently interbreeds with N. gabriellae in central Vietnam (see below). Following the suggestion of Zhang (1997), Groves (2001, 2005) considered it to be a distinct species. It is my opinion, however, that this conclusion is premature, since the evidence was based on only a few specimens: Until additional evidence is reported, Nomascus l. siki should be considered a subspecies. Adult males have small, white cheek-patches that extend as far up as the corners of the eyes, and thin, white hair partially encircles the upper lip and totally encircles the lower lip, connecting on the upper portion of the throat, and terminating at a black chin which can have a few white hairs (Fig. 33). Adult females have few black hairs above the ear, and appear to be more similar in appearance to adult female N. l. leucogenys than to N. gabriellae females (Geissmann 1995), with a thin white face-ring that is wider above the mouth and below the eye, which gives them an older appearance (Fig. 25).

Figure 33.

Nomascus leucogenys siki (southern white-cheeked gibbon) subadult male “Pimkie”, Zoo Mulhouse, France. Photo by Aline Drouin.

Central Vietnam

These two forms have a natural hybrid zone in central Vietnam. Adult and immature males and immature female hybrids look more like N. gabriellae than N. leucogenys siki (Fig. 34), and adult female hybrids have features similar to both N. gabriellae and N. leucogenys siki (Fig. 35). The hybrids can easily be identified by karyotyping (P. vanTuinen pers. comm.).

Figure 34.

Nomascus leucogenys siki × Nomascus gabriellae (wild-born hybrid) juvenile female “Kim Khi”, GCC. Photo by Alan Mootnick.

Figure 35.

Nomascus leucogenys siki × Nomascus gabriellae (natural hybrid) adult female “Demi”, Zoo Mulhouse. Photo by Aline Drouin.

Southern Vietnam, southern Laos, and eastern Cambodia

Nomascus gabriellae has been referred to as the buff-cheeked gibbon (Osgood 1932), red-cheeked gibbon (Groves 1972, 2001, 2005), yellow-cheeked gibbon (Geissmann 1995), and golden-cheeked gibbon (Varsik 2000). Adult males are mainly blackish but generally have dark brown to buffish brown on the upper chest, and can be lighter in color around the nipples. They have small, light buffish white cheek patches that extend to the bottom of the orbital ridge and can be slightly separated at the throat, with black hair under the eyes (Fig. 36). Adult females can be smaller than adult males and Nomascus l. leucogenys females. Adult females are generally buff to strawberry-buff and can have a very slight grizzling of darker hairs on the chest, on the edges and tips of the fingers and toes, and on the outer forearm. Their blackish crown patch can taper down the nape of the neck and sometimes has a few black hairs extending to the center of the scapulae. There is black hair under the eyes, and a black fringe around the ears. Adult females may have slightly red-brown to black genital hairs, with a few slightly red-brown to black hairs surrounding the anus, and usually there is a trace of a white fringe encircling the face.

Figure 36.

Nomascus gabriellae (buff-cheeked gibbon) adult female left “Bahmetoo”, adult male right “Koo”, Los Angeles Zoo, California. Photo by Alan Mootnick.

Myanmar west of the Chindwin River, northeastern India, and northeastern and southeastern Bangladesh

Juvenile through adult males, and juvenile through the beginning stages of subadulthood females are black with a thick, white brow of varying heights that grows upwards, that flicks up at the ends and generally not separated in the middle (Figs. 38 and 39). They have a black chin tuft. The black genital tuft of the adult males grows dorsally to about 52 mm in length, and parts in the middle lengthwise. Some males have slightly longer black hair under and toward the center of the brow, giving the appearance of a separated brow. The infant's white brow is large, with a trace of white along the sides of the head by the end of the first color transition and afterwards, and the chin tuft is pale (Fig. 40). The thick, white brow of the adult female turns upwards at the ends, is narrower as it travels down the orbital ridge and the muzzle, and then connects with the white chin tuft. White hair encircles the bridge of the nose and extends around the muzzle to connect with the chin tuft creating a face ring like a figure of eight. The throat and chest of the adult female is generally darker than the adult female Hoolock leuconedys (eastern hoolock gibbon) (Fig. 41). The hair on the hands and feet of the adult female is generally the same color as the body hair, but there is a black fringe on the fingers, the edge of the hands, and toes (Groves 1972; Mootnick et al. 1987) that encircles the foot, and there is some blackish brown in the genital region (Mootnick and Groves 2005) (Fig. 42) and around the anus.

Figure 38.

Hoolock hoolock (western hoolock) subadult Alipore Zoo. India. Photo by Mike Dee.

Figure 39.

Hoolock hoolock (western hoolock) adult male “Turja” Dhaka Zoo. Bangladesh. Photo by Alan Mootnick.

Figure 40.

Hoolock hoolock (western hoolock) adult female “Lucky” and 14 month old male “Sugrib” Dhaka Zoo. Bangladesh. Photo by Alan Mootnick.

Figure 41.

Hoolock hoolock (western hoolock) adult female “Alfa”,GCC. Photo by Alan Mootnick.

Figure 42.

Hoolock hoolock (western hoolock) adult female “Alfa”, GCC. Photo by Alan Mootnick.

Hoolock leuconedys (Groves, 1967) Eastern hoolock gibbon Myanmar east of the Chindwin River, south western Yunnan, and Lohit District, Arunachal Pradesh, northeast India

Recent surveys confirmed that H. leuconedys also occurs between the Lohit River and the mountains in the Dafa Bum, Arunachal Pradesh, in northeast India in a continuous range into Myanmar (Das et al. 2006). The adult males are black, with a long silvery testicle tuft that parts in the middle lengthwise and is approximately 75 mm long, directed dorsally. The chest of the adult male is grizzled with silverish hair (Fig. 43) that can be seen first when approximately nine years old (GCC HHL304). By the time the adult male has a grizzled, silver chest and the female is completing her final color change, there are two parallel white lines of hair connecting to the medial aspect of the thick, white brow where it is separated in the middle, which descend then diverge to encircle the muzzle and connect with the chin tuft (Figs. 44 and 45). Starting at the outer aspect of the thick, white brow of the adult female, there is white hair encircling the orbital ridge that runs just above the diverging white line of hair above the bridge of the nose that then connects at the medial aspect of the brow. This gives the female the appearance of a double figure of eight face ring (Fig. 45). The hands and feet of the adult female are slightly paler than the limbs, and may have a trace of white (Groves 1972) (Fig. 44). The adult female sometimes has a lighter coloration running through the center of the light brown chest hair (Fig. 43); the digits may have a trace of black on them; and the crown hair is lighter and grows slightly upwards and toward the nape of the neck and is slightly directed toward the sides of the head (Fig. 46) (Mootnick et al. 1987). The adult female's genital region is generally lighter in color compared to the surrounding area, whereas the hair surrounding the anus is brown. Some females from Yunnan and the east of the Chindwin River have been observed to have brown hair on the genital region. At subadulthood, the male begins to acquire a brownish color to the hair on the chest, and the testicle tuft is beginning to lengthen with silverish hair. Before the chest turns brown, the thin, face-ring slowly decreases on the sides of the face, and white hairs begin to encircle the bridge of the nose, and eventually connect with the white hairs under the chin. At this time the white brow is beginning to thicken above the orbital ridge. Immatures in the black color phase have white chin hairs and a large, white brow separated in the middle, with white hair along the lateral aspect of the orbital ridge, giving the appearance of a face ring (Fig. 45).

Figure 43.

Hoolock leuconedys (eastern hoolock) adult male “Arthur” and adult female “Betty”, GCC. Photo by Erin Bell.

Figure 44.

Hoolock leuconedys (eastern hoolock) adult male “Arthur” and adult female “Betty”, GCC. Photo by Erin Bell.

Figure 45.

Hoolock leuconedys (eastern hoolock) adult female “Drew”, GCC. Photo by Erin Bell.

Figure 46.

Hoolock leuconedys (eastern hoolock) juvenile female left “Drew”, juvenile male right “Chester”, GCC. Photo by Alan Mootnick.

Mentawai Islands, Indonesia

Both sexes have short, black hair, and are known to remain this color at all life stages. Hylobates klossii has a broad chest and long legs, thumbs, and big toes (Groves 1972) (Fig. 47). The hair forming the genital tuft is short. There is inter-digital webbing on the feet (Groves 1972), but it only extends approximately one-third of the way along the proximal phalange between the second and third digits (Fig. 48). Adults have the most compact skull, smallest jaw, and teeth in comparison to other gibbons (Marshall and Sugardjito 1986). The hair on top of the head is flat. Immature crown hair stands erect (Fig. 49). The spectacular great call of the adult female H. klossii is more similar to those of female H. pileatus and H. muelleri than it is to female H. lar, H. albibarbis and H. agilis. No subspecies have been described, but there are some variations in hair length, the direction of hair grown on the outer side of the forearm, and in body size on different islands (Groves 1972, 1984). Of the four captive females observed, two were in transition from juvenile to adulthood (A. Mootnick pers. obs.). When one of the females became a young adult she had a slight tawny-colored grizzling on the chest (Fig. 50).

Figure 47.

Hylobates klossii (Kloss' gibbon) adult female, Lion County Safari, California. Photo by staff photographer.

Figure 48.

Hylobates klossii (Kloss' gibbon) female “Nanam”, Gibbon Foundation, Indonesia. Slight interdigital webbing between the second and third digits. Photo by David Broadhurst.

Figure 49.

Hylobates klossii (Kloss' gibbon) infant, South Pagai. Photo by Richard Tenaza.

Figure 50.

Hylobates klossii (Kloss' gibbon) 8 yr old female “Nanam”, Gibbon Foundation, Indonesia. Photo by Micca Rogers.

Western Cambodia, southeastern Thailand, and southwestern Laos

Hylobates pileatus is the most sexually dichromatic of the gibbons in the Hylobates group. Adult males have short, black hair with a thick, white brow band that becomes thinner as it encircles the face. The fingers and toes of the adult males are white, with a slight fringe running halfway up the sides of the hands and feet (Fig. 51). There is a white prepubertal patch. The crown cap is encircled by a grizzled, light, sliverish streak on the sides of the head that becomes faint on the back of the head, with a few white hairs on the nape, shoulder and upper back. Adult males may have a faint, gray grizzling on the lower back and lower legs. Subadult and adult females are silver-buff with a black, heavily furred throat, and an inverted triangle on the ventrum that branches off to the underarm area but stops short of the genital region (Figs. 1 and 52). This black coloration extends upwards to the bottom of the ears and narrows in front of the ear to connect with the cap. The cap of the female is large and black, with long, silverbuff hair curved over the temples. Subadult and adult females have a white brow (which becomes thinner depending on age, physical condition or pregnancy) (Figs. 52, 53, 54 and 55) that sometimes extends laterally around the orbital ridge; there can be a trace of a white facial ring (Fig. 52). Since infants do not have bi-colored hair (darker hair at the base), they are lighter buff than subadults and adult females (Figs. 1, 53 and 55). Infants, as in all hylobatids, initially have some light creamypink skin (Fig. 54) that turns various darker colors depending on the species and parts of the body. During infancy the palms, soles and face turn to a tawny gray (Fig. 1) and, depending on age and amount of sunlight exposure, they end up having a charcoal-gray pigmentation.

Figure 51.

Hylobates pileatus (pileated gibbon) adult male “Birute”, GCC. Photo by Alan Mootnick.

Figure 52.

Hylobates pileatus (pileated gibbon) 52 month old female “Kanako”, GCC. Photo by Erin Bell.

Figure 53.

Hylobates pileatus (pileated gibbon) adult female “JR” in first trimester, 23 month old male “Truman”, GCC. Photo by Erin Bell.

Figure 54.

Hylobates pileatus (pileated gibbon) adult female “JR”, 1 day old female “Jitka”, GCC. Photo by Erin Bell.

Figure 55.

Hylobates pileatus (pileated gibbon) adult female “Tuk”, GCC. Photo by Erin Bell.

Hylobates pileatus is the only species in the genus in which males undergo a complete color change from infancy to adulthood (buff to black). Both males and females begin their color change at about 10–12 months old. The change starts at either the center of the chest or the crown (Figs. 53 and 56). At 9.5 months old, black hair was noticeable on the crown of one female (GCC Jitka) but not on the chest. The first signs of black on the center of the throat closest to the chest plate were observed for a male at 37 months old, and the white brow and a partial face ring became evident (GCC Truman). The females can complete their color change at 4 years of age (Fig. 52), whereas the process is still ongoing in males when 4.5 years old (Fig. 57). Both sexes have a lateral tuft along the sides of the crown. By seven years of age, the female's crown hair has lengthened to the point that it hangs over the temples (Figs. 53 and 54), which Marshall and Sugardjito (1986) referred to as Dagwood tufts. In some females the tuft curls upwards (Fig. 55). Males complete their color change by 6.5 years of age (GCC Kokopelli, Mateus Binti); the lower back and lower limbs are the last areas where the color change is noticeable (Fig. 58).

Figure 56.

Hylobates pileatus (pileated gibbon) adult female “JR”, 32 month old male “Truman”, GCC. Photo by Erin Bell.

Figure 57.

Hylobates pileatus (pileated gibbon) 4 yr 6 mo male “Kokopelli”, GCC. Photo by Alan Mootnick.

Figure 58.

Hylobates pileatus (pileated gibbon) 5 year 7 month old male “Mateas Binti”, GCC. Photo by Erin Bell.

Western and central Java

Both sexes are silvery gray, and generally have long, dense hair at the neck, sides of the head, upper arms, and on the shoulders. The hair length between the shoulders ranges from 50 mm to 70 mm (Groves 1968). The outer hair coloration can turn a mouse gray in harsh sunlight. Either sex may have a distinct light-to-blackish gray cap depending on whether they are from central or western Java, and the same dark coloration as the cap is occasionally seen under the whitish brow. There is charcoal-gray hair in the genital region and surrounding the anus. The female's chest is sometimes charcoal- gray colored (Fig. 59) (Geissmann 1995). The transition from a gray chest to a dark chest plate can begin as early as 5 years old at the center of the chest, and can eventually resemble a wide, inverted triangle that tapers towards the abdomen and becomes a line as it gets closer to the groin (GCC Chloe) or observed only on the upper chest (GCC Khusus). An adult male from central Java (MZB 3320) has a thin charcoal-gray colored vertical streak running down the center of the chest. Immature chest coloration darkens from a light, silverish gray to silver gray, or gray by the time they are mature. Both sexes have white to white-gray hair on the brow and surrounding the chin; this hair usually connects to slightly darker hair on the side of the face to form a face ring (Fig. 60). Hair under the chin grows upward, giving the appearance of a “goatee”. Infants are lighter in color than adults and change to silvery gray shortly after birth (Figs. 59 and 61) (Groves 1972) and their cap darkens as they mature (Figs. 61 and 62). Hylobates moloch is sometimes confused with H. muelleri because of similarities in coat color. However, the great call of the female H. moloch is more similar to those of female H. agilis, H. albibarbis, and H. lar than it is to H. muelleri.

Figure 59.

Hylobates moloch (Javan gibbon) adult female “Chloe”, 1 day old male “Lionel”, GCC. Photo by Alan Mootnick.

Figure 60.

Hylobates moloch (Javan gibbon) adult male “Chilibi”, GCC. Photo by Suzanne Kokel.

Figure 61.

Hylobates moloch (Javan gibbon) adult female “Chloe”, 6 month old male “Reg”, GCC. Photo by Alan Mootnick.

Figure 62.

Hylobates moloch (Javan gibbon) 3 yr old male “Lionel”, 6 year 10 month old male “Isaac”, GCC. Photo by Clare Cunningham.

Following the suggestion of Andayani et al. (2001; see also Supriatna et al. 1999; Supriatna 2006), Brandon-Jones et al. (2004) listed two subspecies of H. moloch: H. m. moloch, the west Javan silvery gibbon, and H. m. pongoalsoni Sody, 1949, the central Javan silvery gibbon. I do not consider them here, and they are not recognized by Groves (2001, 2005) or Geissmann et al. (2002). Hylobates m. pongoalsoni has a lighter cap than the gibbons of western Java. Research on their vocalizations, and additional molecular genetic and chromosome studies may shed further light on this (Geissmann et al. 2002).

Borneo, except for the southwest

Adult male and female Hylobates muelleri are similar in their coat color, which varies from gray to gray-brown, or blackish. The hair of the adult male's genital tuft is 25 mm long (Marshall and Sugardjito 1986) and is typically darker than the body hair. Infant coat color is lighter than the parents (Fig. 63). This species lacks a uniform appearance in areas of geographic overlap with other Müller's gibbon subspecies. The great call of the female is somewhat similar to that of female H. pileatus.

Figure 63.

Hylobates m. muelleri (eastern Müller's gibbon) adult female “Dongkey”, 1.5 month old infant, Kalaweit. Photo by Wandy.

Marshall and Sugardjito (1986) recognized three subspecies (see Groves 2001, 2005), which we list here. Some people have difficulties distinguishing two of them, H. m. muelleri (Eastern Müller's gibbon), and H. m. abbotti (Abbott's gray gibbon) from H. moloch because of similarities in coat color. Hylobates m. funereus (northern Müller's gibbon) is occasionally misidentified as H. albibarbis for the same reason.

Southeastern Borneo

Hylobates m. muelleri is pale gray or gray-brown, with a thick, white brow that is wider at the center. The cap is blackish, and can grow slightly down the nape with black grizzling through the gray hair as it approaches the center of the back. The ventrum, abdomen, genitals, hands or just the fingers, and toes are blackish (Fig. 63). The outer portion of the legs and arms are gray to gray-brown, and the inner aspects of the limbs are darker in color (Figs. 63 and 64), and vary between individuals.

Figure 64.

Hylobates m. muelleri (eastern Müller's gibbon) subadult male, Taman Safari, Indonesia. Photo by Alan Mootnick.

Northern Borneo

Hylobates m. funereus is dark gray or gray-brown with a blackish to blackish-brown cap, ventrum, throat, inner aspects of the limbs (which can vary between individuals), anus, and genitals (Fig. 65). The outer area of the lower limbs, elbow, and tips of the fingers, toes, and in some individuals the back, can be paler in color. They have a large, white brow that is wider at the center. Toes and fingers are black on specimens from southern regions where the subspecies overlaps geographically with H. m. muelleri. There is a report of a very large Hylobates m. funereus and a blackish color phase in the Kinabatangan Wildlife Sanctuary (Ancrenaz 2001).

Figure 65.

Hylobates muelleri funereus (northern Müller's gibbon) adult female “Abbey”, GCC. Photo by Alan Mootnick.

Western Borneo

Hylobates m. abbotti has short, mouse-gray body hair, and can have dark hair in the genital region (Fig. 66), while the lumbar region can be slightly lighter than the upper back. The brow is slightly paler than the head hair and it can have blackish hair below the brow and above the eyes. Populations closer to the bordering area of H. m. funereus sometimes have blackish hair on the throat, fingers, and toes, and a slightly darker cap (Fig. 67), and upper chest and inner aspects of the limbs, reflecting a possible subspecific hybridization in areas of overlap. The H. muelleri that were found in Sarawak 4th Division, Ulu Selio at an elevation of 3,500 feet (FMNH 88551-60) somewhat resembles both H. m. abbotti and H. m. funereus.

Figure 66.

Hylobates muelleri abbotti (Abbott's Müller's gibbon) adult female and infant, Singapore Zoo. Photo by Roland Wirth.

Figure 67.

Hylobates muelleri abbotti (Abbott's Müller's gibbon) adult male “Hylo”, Edinburgh Zoo, Great Britain. Photo by Elliott Haimoff.

Sumatra, south from Lake Toba, and Malay Peninsula between the Perak and Mudah rivers

Marshall and Sugardjito (1986) and Brandon-Jones et al. (2004) list three subspecies of H. agilis: H. a. agilis (the mountain agile gibbon); H. a. unko (lowland agile gibbon); and H. a. albibarbis. Groves (2001, 2005) lists albibarbis as a full species on the basis of morphological and pelage differences. Hirai et al. (2003, 2005) reinforce this view and I follow Groves' (2001) recommendation in this case. Based on similarities in the vocalization and some aspects of the pelage, J. T. Marshall maintains the view that the form albibarbis is a subspecies of H. agilis; an arrangement suggested earlier in Marshall and Marshall (1976) (J. T. Marshall pers. comm. 2005–06). Groves (2001, 2005) listed unko as a junior synonym of H. agilis.

With a captive weight of as little as 5.8 kg (GCC Mumma), some adult Hylobates agilis can be considered the smallest of the gibbons.. Males and females have very prominent orbital ridges (Griffith 1827), can be either buffish, buffish with darker underparts, brownish, reddish, blackish, or with a lighter colored lumbar region (Fig. 68). Immature through adult males and immature females have whitish brows and cheek patches, which resemble a beard (Fig. 69). The hair of the adult male's genital tuft is 50 mm long, and is generally the same color as, or slightly paler than, the body hair (Marshall and Sugardjito 1986). Starting at the chin, females begin to lose their cheek patches at approximately 6 years old, and finish their color change between 7 and 14 years old (Fig. 70). Adult females who have been housed in low light conditions, who are pregnant or lactating, or who have nutritional deficiencies, may lack the white brow and if in black pelage they could resemble H. klossii. The lumbar region and rump of young infants are mixed with slightly lighter coloration. H. agilis can have webbing between the second and third toe on the proximal phalanges (Elliot 1913) (Fig. 71). The female's great call is similar to female H. albibarbis and somewhat similar to the female H. lar.

Figure 68.

Hylobates agilis (agile gibbon) adult female and infant, Singapore Zoo. Photo by staff photographer.

Figure 69.

Hylobates a. agilis (mountain agile gibbon) juvenile female “Ruby Baby”, GCC. Photo by Alan Mootnick.

Figure 70.

Hylobates a. agilis (mountain agile gibbon) 12 year 4 month old female “Ruby Baby” and 6 day old male “Milton”, GCC. Photo by Donald Johanson.

Figure 71.

Hylobates a. agilis (mountain agile gibbon) adult male “Bebopen Baby”, GCC. Photo by John Williams.

Marshall and Sugardjito (1986) concurred with Wilson and Wilson (1977) that there is a high percentage of Hylobates agilis in black pelage east of the Barisan Mountains, in the swamp forests and eastern lowlands of Sumatra, and in west Malaysia, and that there is a high percentage of light-colored phase Hylobates agilis in the mountainous range of the Barisan Mountains, which is the native habitat of the robust black Symphalangus syndactylus. For this reason Marshall and Sugardjito (1986) confirmed that Hylobates agilis unko is located east of Barisan Mountains and west Malaysia, and H. a. agilis occurred in the mountainous range of west Sumatra. It is possible that sympatry with S. syndactylus in west Sumatra, is the reason for the occurrence of the lighter form, H. a. agilis.

I have also found a small but observable difference between the facial pelage of H. agilis in the mountains and lowlands of Sumatra and Malay Peninsula (Mootnick et al. 1996, A. Mootnick, in prep.). Distinct differences exist in the color and amount of white surrounding the face or on the brow in museum specimens from Sumatra and Malay Peninsula, when compared with live specimens. My preliminary notes on museum specimens indicate that elevation plays a role in the amount of white on the brow and/or cheek patches, or shade of white on the cheek patches, an aspect which has led to me to give the common names for the Hylobates a. agilis (mountain agile gibbon) and H. agilis unko (lowland agile gibbon) (Mootnick et al. 1996). H. agilis is easily determined through G-banding when compared with the chromosomes of other Hylobates gibbons (vanTuinen et al. 1999) and in C-banding analysis (Hirai et al. 2003).

Highlands of northern Malay Peninsula and western Sumatra south of Lake Toba

The pelage of H. a. agilis is buff, reddish-orange, reddish- brown, brown or blackish. My observations indicate that the adult males and immature males and females have white cheek patches that generally connect under the chin and brow (Fig. 72). The adult female's brow is wide and white, tapering towards the ends, and not divided in the middle (Fig. 73).

Figure 72.

Hylobates a. agilis (mountain agile gibbon) adult male “Sonny”, GCC. Photo by Suzanne Kokel.

Figure 73.

Hylobates a. agilis (mountain agile gibbon) adult female “Mumma” and infant male “Albert”, GCC. Photo by Shawn Tanaka.

Lowlands of northern Malay Peninsula and eastern Sumatra south of Lake Toba

Hylobates agilis unko possesses few characteristics that reliably distinguish it from H. a. agilis. Based on a preliminary study, the cheek patches are creamy-white to a grizzled white, sparser than Hylobates a. agilis, and do not connect under the chin or brow (Fig. 74). The adult female's brow marking is thin and short and can be separated in the middle. The lumbar region is paler than the rest of the body in some Hylobates a. unko.

Figure 74.

Hylobates agilis unko (lowland agile gibbon) adult male “Homer”, GCC. Photo by Alan Mootnick.

Southwestern Borneo

First described as a subspecies of H. muelleri (Lyon 1911), Marshall and Sugardjito (1986) and Brandon-Jones et al. (2004) listed this gibbon as a subspecies of H. agilis (see above). Overall, H. albibarbis varies in shades of light brown with a large, dark brown cap and darker brown under parts, with the lower back being buffish in color (Lyons 1911). The description that follows was compiled from museum specimens. The hands and feet vary from brown to blackish brown with darker fingers and toes. The brow is whitish and can be separated. Immature and adult males have white to creamywhite cheek patches. The chest and abdomen are dark-brown. The lower back is buff (Fig. 75). The shoulders, upper back, and from the nape to the back of the ear, vary in shades of tawny. The front portion of the sides of the face up to the front of the ear is brown. The throat varies from light to dark brown. The rump and hips vary from brown to tawny. The outer portion of the legs are tawny, and are generally darker on the inner portion. The outer portion of the arm varies from tawny to brown, and the inside of the arm is generally darker. The hair surrounding the anus is brown. The hair surrounding the female's genitals is dark brown, whereas the male's genital tuft is tawny. Because there is so much color variation in this species and since, historically, it has been misidentified with Hylobates muelleri funereus it would be important to confirm the species identification through its vocalizations, karyotype or DNA. The female's song has longer and slower notes when compared with the H. a. agilis and H. a. unko. Karyotyping wild-born, or captive-born individuals whose parents have been confirmed to be H. albibarbis, can easily distinguish this form from H. a. agilis and H. a. unko (vanTuinen et al. 1999; Hirai et al. 2003, 2005).

Figure 75.

Hylobates albibarbis (white-bearded gibbon) adult female “Jackie”, Valley Zoo, Canada. Photo by staff photographer.

Central and southern Malay Peninsula and southern Thailand

Both sexes are generally dark chocolate brown in color, but approximately one-third of the population is creamy-buff (Fig. 78) (Marshall and Sugardjito 1986). The darker hair base ranges from 50–66% of the length of the hair (Groves 1972). The hair length between the shoulders ranges from 36 mm to 55 mm (Groves 1972). The genital region is darker than the body hair. The white hair on the hands and feet extends slightly past the wrist and ankle. The face ring is thin above and on the outer sides of the eyes. It widens at the bottom of the ears, and remains wider as far as the chin. A partial face ring has been observed in some specimens (Blyth 1847; Gulik 1967; Groves 1972), but without genetic testing it is difficult to determine if they are descendents of H. agilis or if this is a phenomenon of this subspecies.

Figure 78.

Hylobates l. lar (Malaysian lar gibbon) subadult male, Zoo Negara, Malaysia. Photo by staff photographer.

Northern Thailand

This subspecies has long hair, and can have more facial hair than the mainland lar gibbon (H. l. entelloides). Silvery base hairs give it a brownish charcoal or white-buff appearance depending on the color phase. These base hairs are deeper in color in the darker color phase, and base hairs are up to 50% of the hair length (Groves 1972). Hylobates l. carpenteri has a white face ring. The pubic region is similar in color to the rest of the body, with few white hairs. The white on the hands and feet can extend up to the wrists and ankles (Groves 1968). Hair length between the shoulders varies from 79 mm to103 mm (Groves 1968).

Central and southern Thailand, and southeastern Myanmar

Hylobates l. entelloides can be blackish, tawny, or blackish brown with a brownish chest and a trace of white hairs on the nape, with brownish buff with slight grizzling of black hairs on body, or overall buff in coloration (Fig. 79). The hair base extends to about one-third up the hair shaft (Groves 1972). Hair length between the shoulders varies from 29 mm to 56 mm (Groves 1968). The white face ring can vary in width depending on the geographical location, and is wider on the sides of the face and chin. The hands and feet are whitish and can be grizzled with the color of the body hair. A trace of the body hair color on the back of the wrist can also taper (almost forming a triangle) towards the knuckles. The black color phase of this subspecies is darker than the dark phase of H. l. lar or H. lar carpenteri. Some black color phase males have grizzled white hair in the genital tuft.

Figure 79.

Hylobates lar entelloides (Thai lar gibbon) (born in northeast Thailand) adult female “Judy”, GCC. Photo by Alan Mootnick.

Northern Sumatra, north of Lake Toba

Unlike the other lar gibbons, H. l. vestitus lacks a dark color phase. The Sumatran lar gibbon varies in color from red-buff, to red-brown, to light-brown, with a slightly darker crown, scapular, genital region, forearm, calf, and throat, and a paler lumbar region (Fig. 80) (Marshall and Sugardjito 1986), or white grizzling through the body. The hair length between the shoulders range from 44 mm to 60 mm (Groves 1972). The white on hands and feet has a slight grizzling of the body hair, and was observed to have the white not extending up to the wrist or the ankle, or extending past the wrist. The face ring is white and medium in size.

Figure 80.

Hylobates lar vestitus (Sumatran lar gibbon) juvenile, Tapaktuan, Indonesia. Photo by Elsie Marshall.

Hylobates lar yunnanensis Ma and Wang, 1986 Yunnan lar gibbon South western Yunnan Hylobates l. yunnanensis differs from the other subspecies in having the lighter base hairs extend only to 10–20% of the hair length (Ma and Wang 1986). The pelage of the pale phase is creamy in color and can have a darker tone ranging from buff to tawny buff to brownish buff on the cap, chest, legs, and outer aspects of the arms. There is a trace of brown to reddish brown hair in the genital region. The hair is longer on the scapular and shoulders. Hands and feet are white. Hair length on the upper back is 120–150 mm (Ma and Wang 1986). Brandon-Jones et al. (2004) point out that H. l. yunnanensis may be a synonym of H. l. carpenteri. This, one would hope, can be resolved by a comparative morphological and DNA study.