, ▁prefer ring ▁rain for est ▁with ▁trees ▁of ▁the ▁family ▁D ip ter oc ar pace ae . ▁ ▁It ▁comes ▁to ▁the ▁ground ▁less ▁frequently ▁than ▁most ▁other ▁leaf ▁mon keys . ▁ ▁It ▁lives ▁in ▁both ▁primary ▁and ▁secondary ▁forest , ▁and ▁also ▁in ▁sw amp ▁for ests ▁and ▁mang ro ve ▁for ests , ▁and ▁even ▁in ▁rub ber ▁plant ations . ▁ ▁It ▁moves ▁primarily ▁by ▁walking ▁on ▁all ▁f ours ▁and ▁by ▁le aping . ▁ ▁According ▁to ▁wild life ▁research er ▁Charles ▁Francis , ▁it ▁typically ▁lives ▁in ▁groups ▁of ▁ 3 ▁to ▁ 6 . ▁ ▁However , ▁a ▁study ▁in ▁Per aw ang , ▁Sum atra ▁found ▁an ▁average ▁group ▁size ▁of ▁ 1 1 ▁mon keys ▁in ▁mixed - sex ▁groups . ▁ ▁The ▁latter ▁study ▁also ▁found ▁an ▁average ▁ratio ▁of ▁ 1 ▁adult ▁male ▁to ▁ 4 . 8 ▁adult ▁females ▁in ▁mixed - sex ▁groups ▁and ▁a ▁ratio ▁of ▁ 1 . 2 5 ▁adult ▁mon keys ▁for ▁every ▁imm ature ▁mon key ▁in ▁mixed - sex ▁groups . ▁ ▁It ▁also ▁found ▁an ▁average ▁range ▁size ▁for ▁a ▁group ▁of ▁ 2 2 ▁hect ares , ▁and ▁an ▁average ▁population ▁density ▁of ▁ 4 2 ▁mon keys ▁per ▁square ▁kilometer . ▁ ▁Other ▁studies ▁found ▁somewhat ▁smaller ▁home ▁ranges , ▁of ▁between ▁ 9 ▁and ▁ 2 1 ▁hect ares . ▁ ▁The ▁R aff les ' ▁band ed ▁lang ur ▁has ▁a ▁primarily ▁veget arian ▁di et .