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5. Identification Key

It should be noticed that even with this key presented below, species identification of some adult gibbon individuals may remain problematic if based solely on characteristics of fur colouration. Some Hylobates muelleri abbotti, for instance, show a considerable resemblance to H. moloch (especially to males), many H. albibarbis resemble H. muelleri muelleri, and some dark H. muelleri funereus are very similar to the dark phase of H. agilis. These problems can usually be resolved easily if vocal characteristics of the animals in question are also used for the identification process. These characteristics are described in the Sound Gallery.

Subspecies identification is, in many cases, even more difficult. This may, to some degree, be related to questionable subspecies descriptions, in the first place, as indicated in Table 2 (see also the Photo Gallery). Of other subspecies, we simply do not know enough diagnostic criteria, often making it impossible to identify individual animals of unknown provenience. For instance, the number of adult females of N. siki available in zoos and museum collections is not sufficient to determine which fur characteristics, if any, reliably distinguish it from female N. leucogenys. No individuals of N. nasutus and N. hainanus are currently known to exist in captivity. In some populations of this species, females lack the dark ventral fur of N. concolor and, thus, show a striking similarity to females of N. leucogenys and N. siki, although they clearly differ from the latter in their song (Geissmann, 1996, 1997; Geissmann et al., 2000).

Future studies may reveal more reliable characteristics for subspecies identification. A particular potential in this respect may be expected from molecular studies using hair roots (e.g. Garza & Woodruff, 1992, 1994), but the method is still expensive.

The following identification key includes all currently recognised gibbon species, but applies to adult individuals only. The body weights refer to adult wild animals (Geissmann, 1993); body weights of adult zoo gibbons may be slightly higher. Colour plates of all species and some subspecies and additional notes on the identification of selected subspecies are provided elsewhere on this site (see Photo Gallery).

Characteristics
Species names are linked to the Photo Gallery

1a

Completely black, without light pattern:
2

1b

Not black or not completely black:
5

x

2a

Body weight 8-15 kg;
Large, inflatable throat sac;
Males with long genital tuft (ca 13.5 cm):
S. syndactylus

2b

Body weight lower than 11 kg,
Throat sac very small or absent;
Genital tuft in males short and inconspicuous (less than 6 cm):
3

x

3a

Body weight 5-7 kg;
No throat sac;
Crown fur without crest:
H. klossii

3b

Body weight 6-10 kg;
Throat sac very small and visible only when inflated during certain vocalisations;
Crown fur stands straight up, with prolonged hairs forming a crest:
4

4a

Fur on chest black:
N. concolor, or N. hainanus, males

4b

Fur on chest rusty brown, not black:
H. nasutus, male

x

5a

Almost completely black, but with light (whitish or yellowish) elements (facial pattern, genital tuft, hands and feet):
6

5b

Not dominantly black:
13

x

6a

Crown fur stands straight up, with prolonged hairs forming a crest;
Body weight 6-10 kg;
Light cheek beard:
7

6b

Crown without crest;
Body weight 4-9 kg;
Light cheek beard present or absent:
9

x

7a

Cheek beard pale yellow or orange, standing out on sides as if "brushed" outwards, with the hairs spreading out from the corners of the mouth like a fan;
Fur on chest rusty brown, not black:
N. gabriellae, male

7b

Cheek beard white, rarely pale yellow, not "brushed" outwards;
Fur on chest black:
8

8a

Light cheek beard lerge, extends up as high as the upper margin of the ear;
No white bracket-shaped patch of fur around corner of mouth:
N. leucogneys, male

8b

Light cheek beard smaller, extends up only as high as the lower margin of the eye;
White bracket-shaped patch of fur around corner of mouth:
N. siki, male

x

9a

Fur on hands and feet white:
10

9b

Fur on hands and feet not white:
11

x

10a

White face ring relatively broad and usually complete;
No light corona around crown of head;
Hands and feet white up to wrist and ankle, respectively;
Genital tuft not white:
H. lar

10b

White face ring relatively thin, broad only above eyes;
Light corona around crown of head;
Hands and feet white only distally of wrist and ankle, respectively;
White genital tuft:
H. pileatus, male

x

11a

White brow band;
Body weight 6-9 kg;
No light cheeks;
Distinct goatee beard;
Long genital tuft (ca 7.5 cm):
12

11b

White or grey brow band (often reduced in older females);
Body weight 4.5-7 kg;
Males often with light cheeks (grey or whitish), females often without these;
No distinct goatee beard;
Males with distinct, but relatively small genital tuft (ca 5 cm):
H. agilis

12a

Fur on chest blackish;
Genital tuft blackish;
Chin black;
White brow streaks close together and may connect above the nose:
H. hoolock, male

12b

Fur on chest usually brownish;
Genital tuft buffy or grizzled;
Chin often exhibits whitish hairs;
The white brow streaks of adult males are well separated with no white hairs between:
H. leuconedys, male

x

13a

Back and limbs pale yellow, yellow, orange or beige brown, not grey or dark brown;
Black cap usually set off sharply from surrounding lighter fur, with crown fur (including cap) standing straight up;
Body weight 6-10 kg:
14

13b

Back and limbs pale yellow, yellow, orange or beige brown, but also grey or dark brown;
Black cap, if present, with crown hairs lying flat
Body weight 4-9 kg:
17

x

14a

Fur on chest (and sometimes belly) black or dark brown, contrasting with light back:
15

14b

Fur on chest and belly light, as back:
16

15a

Light face ring inconspicuous;
Black cap not connected to dark facial area; dorso-caudally extending not further than neck:
N. concolor, female

15b

Light face ring broad and conspicuous;
Black cap connected to dark facial area; dorso-caudally extension large, down to area between shoulder blades:
N. nasutus, female

x

16a

Face ring usually yellowish (rarely white), often not contrastingly lighter than neck or incomplete;
Cheek fur usually standing out on sides, as if "brushed" outwards, with the hairs spreading out from the corners of the mouth like a fan:
N. gabriellae, female

16b

Face ring usually white and distinctly lighter than neck, often thin, but usually complete;
Cheek fur not standing out on sides:
N. leucogenys, N. siki , N. hainanus, females

x

17a

Crown fur lying flat and being light beige, contrastingly lighter than dark brown cheeks;
Body weight 6-9 kg;
A thin stripe of white hair starts from cheeks and crossing the face below the eyes goes upwards across the nasal ridge;
Distinct light goatee beard:
18

17b

Crown fur variably lying flat or standing up, not contrastingly lighter than cheeks;
Body weight 4-8 kg;
No stripe of white hair below eyes and across nasal ridge
With or without distinct light goatee beard:
19

18a

Fur on feet same colour as lower leg:
H. hoolock, female

18b

Feet often with contrastingly lighter fur:
H. leuconedys, female

x

19a

Cap and ventral area black, both sharply set off from surrounding light grey fur; ventral shield three-cornered, with lower tip reaching genital area;
Back and limbs light grey or cream;
No light face ring; thin white brow band may be present but is usually lacking;
Long, white temple fringes hanging over black cheek region and ears:
H. pileatus, female

19b

Cap and ventral area may or may not be darker than surrounding fur; if these areas are black, they are rarely set off sharply and the ventral area has no distinctly three-cornered pattern;
Back and limbs light or dark, of variable colouration;
With or without light face ring; light brow band usually present;
No long, white temple fringes hanging over black cheek region and ears:
20

x

20a

White hands and feet;
Fur colouration variable: pale yellow, yellow, beige brown, hazel, dark brown (or black, see also 10a), but not grey;
Usually no dark cap and no dark ventral area (if present, these areas are brown or dark brown, not blackish);
Face ring white and usually complete:
H. lar

20b

Hands and feet not white;
Fur colouration variable like 20a, but may also be grey;
With or without dark (dark brown or blackish) cap and dark ventral area;
Face ring only partly white, usually incomplete, often reduced to brow band:
21

x

21a

Silvery grey fur colouration; only cap and ventral area may be contrastingly darker (dark-gray or black) in some animals;
Brow band broad and whitish, usually distinct and sharply set off, pointed laterally of the eyes;
Distinct, forward projecting, whitish goatee beard:
H. moloch

21b

Fur colouration variable; grey individuals are mouse grey rather than silvery grey; cap, underparts and limbs may be contrastingly darker (dark grey, blackish brown or black) than back; hands and toes contrastingly black in some animals;
Brow band variable in both colouration (whitish, light grey, light buff) and extent (broad, thin, absent);
No distinct, forward projecting, whitish goatee beard:
22

x

22a

Fur colouration variable: mouse grey, grey brown, hazel, or dark brown, but not yellow;
Feet may be distinctly paler than legs in some animals (but not white as in H. lar);
Light brow band very variable in its extent, more or less distinct, but rarely missing;
Usually no distinctly light cheek patches;
Genital tuft of male very small (ca 2.5 cm) and usually blackish:
H. muelleri

22b

Fur colouration variable: pale yellow, yellow, beige brown, grey brown, nut-brown, dark brown (or almost black, see also 11b);
Feet not distinctly paler than legs;
Brow band usually white, but may be completely absent in older blackish females;
Males often with grey, whitish or pale brownish cheek patches (often joined under the chin), females often without these;
Males with distinct, but relatively small genital tuft (ca 5 cm) which may be of contrastingly light colour in some brown animals (intermediate phase), but not contrasting with ventral fur in others:
23

23a

Fur colouration variable: pale yellow, yellow, beige brown, grey brown, nut-brown, dark brown (or almost black, see also 11b);
Digits of hands and feet not contrastingly darker than legs;
Ventral area and cap may or may not be contrastingly darker:
H. agilis

23b

Fur colouration variable: grey brown, hazel, or dark brown, but no yellow or black morphs;
Digits of hands and feet contrastingly darker than legs;
Ventral area and cap contrastingly darker, blackish:
H. albibarbis

	Characteristics	Species names are linked to the Photo Gallery
1a	Completely black, without light pattern:	2
1b	Not black or not completely black:	5
x
2a	Body weight 8-15 kg; Large, inflatable throat sac; Males with long genital tuft (ca 13.5 cm):	S. syndactylus
2b	Body weight lower than 11 kg, Throat sac very small or absent; Genital tuft in males short and inconspicuous (less than 6 cm):	3
x
3a	Body weight 5-7 kg; No throat sac; Crown fur without crest:	H. klossii
3b	Body weight 6-10 kg; Throat sac very small and visible only when inflated during certain vocalisations; Crown fur stands straight up, with prolonged hairs forming a crest:	4

4a	Fur on chest black:	N. concolor, or N. hainanus, males
4b	Fur on chest rusty brown, not black:	H. nasutus, male
x
5a	Almost completely black, but with light (whitish or yellowish) elements (facial pattern, genital tuft, hands and feet):	6
5b	Not dominantly black:	13
x
6a	Crown fur stands straight up, with prolonged hairs forming a crest; Body weight 6-10 kg; Light cheek beard:	7
6b	Crown without crest; Body weight 4-9 kg; Light cheek beard present or absent:	9
x
7a	Cheek beard pale yellow or orange, standing out on sides as if "brushed" outwards, with the hairs spreading out from the corners of the mouth like a fan; Fur on chest rusty brown, not black:	N. gabriellae, male
7b	Cheek beard white, rarely pale yellow, not "brushed" outwards; Fur on chest black:	8

8a	Light cheek beard lerge, extends up as high as the upper margin of the ear; No white bracket-shaped patch of fur around corner of mouth:	N. leucogneys, male
8b	Light cheek beard smaller, extends up only as high as the lower margin of the eye; White bracket-shaped patch of fur around corner of mouth:	N. siki, male
x
9a	Fur on hands and feet white:	10
9b	Fur on hands and feet not white:	11
x
10a	White face ring relatively broad and usually complete; No light corona around crown of head; Hands and feet white up to wrist and ankle, respectively; Genital tuft not white:	H. lar
10b	White face ring relatively thin, broad only above eyes; Light corona around crown of head; Hands and feet white only distally of wrist and ankle, respectively; White genital tuft:	H. pileatus, male
x
11a	White brow band; Body weight 6-9 kg; No light cheeks; Distinct goatee beard; Long genital tuft (ca 7.5 cm):	12
11b	White or grey brow band (often reduced in older females); Body weight 4.5-7 kg; Males often with light cheeks (grey or whitish), females often without these; No distinct goatee beard; Males with distinct, but relatively small genital tuft (ca 5 cm):	H. agilis

12a	Fur on chest blackish; Genital tuft blackish; Chin black; White brow streaks close together and may connect above the nose:	H. hoolock, male
12b	Fur on chest usually brownish; Genital tuft buffy or grizzled; Chin often exhibits whitish hairs; The white brow streaks of adult males are well separated with no white hairs between:	H. leuconedys, male
x
13a	Back and limbs pale yellow, yellow, orange or beige brown, not grey or dark brown; Black cap usually set off sharply from surrounding lighter fur, with crown fur (including cap) standing straight up; Body weight 6-10 kg:	14
13b	Back and limbs pale yellow, yellow, orange or beige brown, but also grey or dark brown; Black cap, if present, with crown hairs lying flat Body weight 4-9 kg:	17
x
14a	Fur on chest (and sometimes belly) black or dark brown, contrasting with light back:	15
14b	Fur on chest and belly light, as back:	16

15a	Light face ring inconspicuous; Black cap not connected to dark facial area; dorso-caudally extending not further than neck:	N. concolor, female
15b	Light face ring broad and conspicuous; Black cap connected to dark facial area; dorso-caudally extension large, down to area between shoulder blades:	N. nasutus, female
x
16a	Face ring usually yellowish (rarely white), often not contrastingly lighter than neck or incomplete; Cheek fur usually standing out on sides, as if "brushed" outwards, with the hairs spreading out from the corners of the mouth like a fan:	N. gabriellae, female
16b	Face ring usually white and distinctly lighter than neck, often thin, but usually complete; Cheek fur not standing out on sides:	N. leucogenys, N. siki , N. hainanus, females
x
17a	Crown fur lying flat and being light beige, contrastingly lighter than dark brown cheeks; Body weight 6-9 kg; A thin stripe of white hair starts from cheeks and crossing the face below the eyes goes upwards across the nasal ridge; Distinct light goatee beard:	18
17b	Crown fur variably lying flat or standing up, not contrastingly lighter than cheeks; Body weight 4-8 kg; No stripe of white hair below eyes and across nasal ridge With or without distinct light goatee beard:	19

18a	Fur on feet same colour as lower leg:	H. hoolock, female
18b	Feet often with contrastingly lighter fur:	H. leuconedys, female
x
19a	Cap and ventral area black, both sharply set off from surrounding light grey fur; ventral shield three-cornered, with lower tip reaching genital area; Back and limbs light grey or cream; No light face ring; thin white brow band may be present but is usually lacking; Long, white temple fringes hanging over black cheek region and ears:	H. pileatus, female
19b	Cap and ventral area may or may not be darker than surrounding fur; if these areas are black, they are rarely set off sharply and the ventral area has no distinctly three-cornered pattern; Back and limbs light or dark, of variable colouration; With or without light face ring; light brow band usually present; No long, white temple fringes hanging over black cheek region and ears:	20
x
20a	White hands and feet; Fur colouration variable: pale yellow, yellow, beige brown, hazel, dark brown (or black, see also 10a), but not grey; Usually no dark cap and no dark ventral area (if present, these areas are brown or dark brown, not blackish); Face ring white and usually complete:	H. lar
20b	Hands and feet not white; Fur colouration variable like 20a, but may also be grey; With or without dark (dark brown or blackish) cap and dark ventral area; Face ring only partly white, usually incomplete, often reduced to brow band:	21
x
21a	Silvery grey fur colouration; only cap and ventral area may be contrastingly darker (dark-gray or black) in some animals; Brow band broad and whitish, usually distinct and sharply set off, pointed laterally of the eyes; Distinct, forward projecting, whitish goatee beard:	H. moloch
21b	Fur colouration variable; grey individuals are mouse grey rather than silvery grey; cap, underparts and limbs may be contrastingly darker (dark grey, blackish brown or black) than back; hands and toes contrastingly black in some animals; Brow band variable in both colouration (whitish, light grey, light buff) and extent (broad, thin, absent); No distinct, forward projecting, whitish goatee beard:	22
x
22a	Fur colouration variable: mouse grey, grey brown, hazel, or dark brown, but not yellow; Feet may be distinctly paler than legs in some animals (but not white as in H. lar); Light brow band very variable in its extent, more or less distinct, but rarely missing; Usually no distinctly light cheek patches; Genital tuft of male very small (ca 2.5 cm) and usually blackish:	H. muelleri
22b	Fur colouration variable: pale yellow, yellow, beige brown, grey brown, nut-brown, dark brown (or almost black, see also 11b); Feet not distinctly paler than legs; Brow band usually white, but may be completely absent in older blackish females; Males often with grey, whitish or pale brownish cheek patches (often joined under the chin), females often without these; Males with distinct, but relatively small genital tuft (ca 5 cm) which may be of contrastingly light colour in some brown animals (intermediate phase), but not contrasting with ventral fur in others:	23

23a	Fur colouration variable: pale yellow, yellow, beige brown, grey brown, nut-brown, dark brown (or almost black, see also 11b); Digits of hands and feet not contrastingly darker than legs; Ventral area and cap may or may not be contrastingly darker:	H. agilis
23b	Fur colouration variable: grey brown, hazel, or dark brown, but no yellow or black morphs; Digits of hands and feet contrastingly darker than legs; Ventral area and cap contrastingly darker, blackish:	H. albibarbis