Going Bananas (Behaviour)

Group Interaction and Routine

From various studies recorded, Proboscis monkeys generic group consists of one –male and its harem (Adult Females and their offspring), moving often in numbers of 3 to 23 , with some groups even reaching 60 (Bennett & Sebastian 1988; Rajanthan & Bennett 1990; Yeager 1990b; 1992; Bennett & Gombek 1993; Boonratana 1993; Yeager 1995; Boonratana 2002; Murai 2004).131724021.4GW4zC4x.ProboscisMonkeygroupfeed

Their territory generally ranges from 1.3 and 9 km² depending on their population within a given area and the type of environment. (Kawabe & Mano 1972; Salter et al. 1985; Yeager 1989a; Bennett & Gombek 1993; Boonratana 1993; 2000; Sebastian 2000)

And unlike other apes, despite having home ranges encroaching on those of other groups, Proboscis Monkeys do not display aggressive territorial behavior (Yeager 1989a; Bennett & Gombek 1993; Boonratana 1993; 2000). Groups can be seen meeting during the day and travelling together. However playing and grooming are still limited to members of the same group only (Yeager 1992b; Boonratana 2002)

In environments linked with rivers, proboscis monkeys usually sleep near the river with group members sleeping as close to one another as possible. Also, the range of their activities in the day tends to be within a radius of 1 km (Salter et al. 1985; Ruhiyat 1986; Rajanthan & Bennett 1990; Yeager 1990b; Sebastian 2000).

A typical day for a Proboscis Monkey would start with feeding followed by travelling inland for foraging, always returning to the riverside to feed before dark (Bennett & Gombek 1993).


 

Group Rivalry

Aggression

Generally, aggressive behaviours are not usually found when competing groups interact with members within the same group being largely accommodating to each other (Yeager 1992b).

Although serious aggression is very uncommon (chases, slaps, biting), minor aggression (vocalizations, facial threats, postural threats), both between groups and members can usually be seen (Yeager 1990b; 1992b).

proboscis-monkey-males-play-fighting-suzi-eszterhas

 

In one-male groups, males usually intervene in female-to-female aggression (Yeager 1990b). With a study showing in one scenario that the large majority of aggression between them was in disagreement over choice sleeping areas, showing evidence of certain form of hierarchy among the groups females (Boonratana 1993).


COMMUNICATION Proboscis_Monkey_by_fightingferret

Proboscis monkeys are known to communicate via calling, six types of which has been identified to date; the honkhonk to infantalarm call, threat callinfant call, and female call (Kawabe & Mano 1972; Messeri & Trombi 2000). Gender plays a part in the type of calling heard (Messeri & Trombi 2000). Honk along with Honk to infant calls come from males and are mostly in relation to territory or group cohesion. Males when sensing danger are also the ones to give alarm callsThreat calls are given by both genders, but each sex results in a different threat call. Finally, female calls are given by females or juvenile members, normally in response to agitation (Messeri & Trombi 2000).

Conservation Psychology