itate ▁the ▁growth ▁of ▁veget ation ▁and ▁give ▁each ▁island ▁a ▁more ▁natural ▁appearance . ▁On ▁some ▁islands , ▁areas ▁of ▁for aging ▁substr ate , ▁such ▁as ▁b ark , ▁have ▁been ▁provided ▁to ▁facil itate ▁scatter ▁feed ing . ▁ ▁The ▁provision ▁of ▁large ▁view ing ▁windows ▁in ▁the ▁sleep ing ▁qu arters ▁gives ▁the ▁public ▁access ▁to ▁what ▁is ▁generally ▁an ▁off - show ▁area ▁in ▁many ▁zo os . ▁However , ▁there ▁are ▁areas ▁where ▁the ▁animals ▁can ▁hide ▁from ▁the ▁public ▁in ▁order ▁to ▁receive ▁priv acy . ▁ ▁The ▁islands ▁mentioned ▁above ▁are ▁inhab ited ▁by ▁si am ang ▁g ib b ons , ▁red ▁r uff ed ▁lem urs , ▁ring - ta iled ▁lem urs , ▁sp ider ▁mon keys , ▁and ▁C ele bes ▁mac a ques . ▁Each ▁species ▁has ▁un limited ▁access ▁to ▁their ▁out door ▁en clos ures ▁both ▁day ▁and ▁night ▁all ▁year ▁round . ▁ ▁The ▁zoo ▁has ▁succeeded ▁in ▁bre eding ▁the ▁prim ates ▁on ▁these ▁islands . ▁The ▁C ele bes ▁mac aque ▁group ▁have ▁done ▁exception ally ▁well ▁since ▁their ▁introduction ▁to ▁the ▁island , ▁and ▁success ▁has ▁also ▁been ▁achieved ▁with ▁the ▁lem urs ▁and ▁si am angs . ▁ ▁In ▁early ▁ 2 0 0 8 , ▁an ▁or ang ut an ▁escaped ▁her ▁en closure . ▁ ▁She ▁had ▁escaped ▁for ▁an ▁hour ▁and ▁was ▁on ▁top ▁of ▁the ▁Sum at ran ▁t iger ▁n ighth ouse ▁before ▁a ▁group ▁of ▁school ▁children